Publications by authors named "David S Followill"

88 Publications

Practice Patterns of Pediatric Total Body Irradiation Techniques: A Children's Oncology Group Survey.

Int J Radiat Oncol Biol Phys 2021 Aug 2. Epub 2021 Aug 2.

Department of Radiation Oncology, Northwestern University, Chicago, Illinois.

Purpose: The aim of this study was to examine current practice patterns in pediatric total body irradiation (TBI) techniques among COG member institutions.

Methods And Materials: Between November 2019 and February 2020, a questionnaire containing 52 questions related to the technical aspects of TBI was sent to medical physicists at 152 COG institutions. The questions were designed to obtain technical information on commonly used TBI treatment techniques. Another set of 9 questions related to the clinical management of patients undergoing TBI was sent to 152 COG member radiation oncologists at the same institutions.

Results: Twelve institutions were excluded because TBI was not performed in their institutions. A total of 88 physicists from 88 institutions (63% response rate) and 96 radiation oncologists from 96 institutions (69% response rate) responded. The anterior-posterior/posterior-anterior (AP/PA) technique was the most common technique reported (49 institutions [56%]); 44 institutions (50%) used the lateral technique, and 14 (16%) used volumetric modulated arc therapy or tomotherapy. Midplane dose rates of 6 to 15 cGy/min were most commonly used. The most common specification for lung dose was the midlung dose for both AP/PA techniques (71%) and lateral techniques (63%). Almost all physician responders agreed with the need to refine current TBI techniques, and 79% supported the investigation of new TBI techniques to further lower the lung dose.

Conclusions: There was no consistency in the practice patterns, methods for dose measurement, and reporting of TBI doses among COG institutions. The lack of standardization precludes meaningful correlation between TBI doses and clinical outcomes including disease control and normal tissue toxicity. The COG radiation oncology discipline is currently undertaking several steps to standardize the practice and dose reporting of pediatric TBI using detailed questionnaires and phantom-based credentialing for all COG centers.
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http://dx.doi.org/10.1016/j.ijrobp.2021.07.1715DOI Listing
August 2021

Our Experience Leading a Large Medical Physics Practice During the COVID-19 Pandemic.

Adv Radiat Oncol 2021 Jul-Aug;6(4):100683. Epub 2021 Apr 2.

Department of Radiation Physics, MD Anderson Cancer Center, Houston, Texas.

Purpose: To provide a series of suggestions for other Medical Physics practices to follow in order to provide effective radiation therapy treatments during the COVID-19 pandemic.

Methods And Materials: We reviewed our entire Radiation Oncology infrastructure to identify a series of workflows and policy changes that we implemented during the pandemic that yielded more effective practices during this time.

Results: We identified a structured list of several suggestions that can help other Medical Physics practices overcome the challenges involved in delivering high quality radiotherapy services during this pandemic.

Conclusions: Our facility encompasses 4 smaller Houston Area Locations (HALs), a main campus with 8 distinct services based on treatment site (ie. Thoracic, Head and Neck, Breast, Gastrointestinal, Gynecology, Genitourinary, Hematologic Malignancies, Melanoma and Sarcoma and Central Nervous System/Pediatrics), a Proton Center facility, an MR-Linac, a Gamma Knife clinic and an array of brachytherapy services. Due to the scope of our services, we have gained experience in dealing with the rapidly changing pandemic effects on our clinical practice. Our paper provides a resource to other Medical Physics practices in search of workflows that have been resilient during these challenging times.
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http://dx.doi.org/10.1016/j.adro.2021.100683DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8016538PMC
April 2021

NRG Oncology Survey on Practice and Technology Use in SRT and SBRT Delivery.

Front Oncol 2020 27;10:602607. Epub 2020 Nov 27.

Cancer Institute, Allegheny Health Network, Pittsburgh, PA, United States.

Purpose: To assess stereotactic radiotherapy (SRT)/stereotactic body radiotherapy (SBRT) practices by polling clinics participating in multi-institutional clinical trials.

Methods: The NRG Oncology Medical Physics Subcommittee distributed a survey consisting of 23 questions, which covered general technologies, policies, and procedures used in the Radiation Oncology field for the delivery of SRT/SBRT (9 questions), and site-specific questions for brain SRT, lung SBRT, and prostate SBRT (14 questions). Surveys were distributed to 1,996 radiotherapy institutions included on the membership rosters of the five National Clinical Trials Network (NCTN) groups. Patient setup, motion management, target localization, prescriptions, and treatment delivery technique data were reported back by 568 institutions (28%).

Results: 97.5% of respondents treat lung SBRT patients, 77.0% perform brain SRT, and 29.1% deliver prostate SBRT. 48.8% of clinics require a physicist present for every fraction of SBRT, 18.5% require a physicist present for the initial SBRT fraction only, and 14.9% require a physicist present for the entire first fraction, including set-up approval for all subsequent fractions. 55.3% require physician approval for all fractions, and 86.7% do not reposition without x-ray imaging. For brain SRT, most institutions (83.9%) use a planning target volume (PTV) margin of 2 mm or less. Lung SBRT PTV margins of 3 mm or more are used in 80.6% of clinics. Volumetric modulated arc therapy (VMAT) is the dominant delivery method in 62.8% of SRT treatments, 70.9% of lung SBRT, and 68.3% of prostate SBRT.

Conclusion: This report characterizes SRT/SBRT practices in radiotherapy clinics participating in clinical trials. Data made available here allows the radiotherapy community to compare their practice with that of other clinics, determine what is achievable, and assess areas for improvement.
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http://dx.doi.org/10.3389/fonc.2020.602607DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7729187PMC
November 2020

Failure Modes in IROC Photon Liver Phantom Irradiations.

Pract Radiat Oncol 2021 May-Jun;11(3):e322-e328. Epub 2020 Nov 30.

IROC Houston Quality Assurance Center, The University of Texas MD Anderson Cancer Center, Houston, Texas; Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas.

Purpose: Our purpose was to analyze and classify the patterns of failure for irradiations of the Imaging and Radiation Oncology Core photon liver phantom.

Methods And Materials: Imaging and Radiation Oncology Core's anthropomorphic liver phantom simulates multitarget liver disease with respiratory motion. Two hundred forty-nine liver phantom results from 2013 to 2019 were analyzed. Phantom irradiations that failed were categorized by the error attributed to the failure. Phantom results were also compared by demographic data, such as machine type, treatment planning system, motion management technique, number of isocenters, and whether the phantom was a first time or repeat irradiation.

Results: The failure rate for the liver phantom was 27%. From the 68 irradiations that did not pass, 5 failure modes were identified. The most common failure mode was localization errors in the direction of motion, with over 50% of failures attributed to this mode. The second-most common failure mode was systematic dose errors. The internal target volume technique performed worse than other motion management techniques. Failure modes were different by the number of isocenters used, with multi-isocenter irradiations having more failure modes in a single phantom irradiation.

Conclusions: Motion management techniques and proper alignment of moving targets play a large role in the successful irradiation of the liver phantom. These errors should be examined to ensure accurate patient treatment for liver disease or other sites where multiple moving targets are present.
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http://dx.doi.org/10.1016/j.prro.2020.11.008DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8102375PMC
August 2021

Development and validation of an age-scalable cardiac model with substructures for dosimetry in late-effects studies of childhood cancer survivors.

Radiother Oncol 2020 12 17;153:163-171. Epub 2020 Oct 17.

Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, United States; The University of Texas MD Anderson Cancer Center UTHealth Graduate School of Biomedical Sciences, United States. Electronic address:

Background And Purpose: Radiation therapy is a risk factor for late cardiac disease in childhood cancer survivors. Several pediatric cohort studies have established whole heart dose and dose-volume response models. Emerging data suggest that dose to cardiac substructures may be more predictive than whole heart metrics. In order to develop substructure dose-response models, the heart model previously used for pediatric cohort dosimetry needed enhancement and substructure delineation.

Methods: To enhance our heart model, we combined the age-scalable capability of our computational phantom with the anatomically-delineated (with substructures) heart models from an international humanoid phantom series. We examined cardiac volume similarity/overlap between registered age-scaled phantoms (1, 5, 10, and 15 years) with the enhanced heart model and the reference phantoms of the same age; dice similarity coefficient (DSC) and overlap coefficient (OC) were calculated for each matched pair. To assess the accuracy of our enhanced heart model, we compared doses from computed tomography-based planning (ground truth) with reconstructed heart doses. We also compared doses calculated with the prior and enhanced heart models for a cohort of nearly 5000 childhood cancer survivors.

Results: We developed a realistic cardiac model with 14-substructures, scalable across a broad age range (1-15 years); average DSC and OC were 0.84 ± 0.05 and 0.90 ± 0.05, respectively. The average percent difference between reconstructed and ground truth mean heart doses was 4.2%. In the cohort dosimetry analysis, dose and dose-volume metrics were approximately 10% lower on average when the enhanced heart model was used for dose reconstructions.

Conclusion: We successfully developed and validated an anatomically realistic age-scalable cardiac model that can be used to establish substructure dose-response models for late cardiac disease in childhood cancer survivor cohorts.
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http://dx.doi.org/10.1016/j.radonc.2020.10.017DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8132170PMC
December 2020

Practice patterns and recommendations for pediatric image-guided radiotherapy: A Children's Oncology Group report.

Pediatr Blood Cancer 2020 10 9;67(10):e28629. Epub 2020 Aug 9.

Department of Radiation Oncology, Northwestern University, Chicago, Illinois.

This report by the Radiation Oncology Discipline of Children's Oncology Group (COG) describes the practice patterns of pediatric image-guided radiotherapy (IGRT) based on a member survey and provides practice recommendations accordingly. The survey comprised of 11 vignettes asking clinicians about their recommended treatment modalities, IGRT preferences, and frequency of in-room verification. Technical questions asked physicists about imaging protocols, dose reduction, setup correction, and adaptive therapy. In this report, the COG Radiation Oncology Discipline provides an IGRT modality/frequency decision tree and the expert guidelines for the practice of ionizing image guidance in pediatric radiotherapy patients.
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http://dx.doi.org/10.1002/pbc.28629DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7774502PMC
October 2020

Sensitivity of IROC phantom performance to radiotherapy treatment planning system beam modeling parameters based on community-driven data.

Med Phys 2020 Oct 16;47(10):5250-5259. Epub 2020 Aug 16.

Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, TX, 77030, USA.

Purpose: Treatment planning system (TPS) dose calculations have previously been shown to be sensitive to modeling errors, especially when treating with complex strategies like intensity-modulated radiation therapy (IMRT). This work investigates the dosimetric impact of several dosimetric and nondosimetric beam modeling parameters, based on their distribution in the radiotherapy community, in two commercial TPSs in order to understand the realistic potential for dose deviations and their clinical effects.

Methods And Materials: Beam models representing standard 120-leaf Varian Clinac-type machines were developed in Eclipse 13.5 (AAA algorithm) and RayStation 9A (v8.99, collapsed-cone algorithm) based upon median values of dosimetric measurements from Imaging and Radiation Oncology Core (IROC) Houston site visit data and community beam modeling parameter survey data in order to represent a baseline linear accelerator. Five clinically acceptable treatment plans (three IMRT, two VMAT) were developed for the IROC head and neck phantom. Dose distributions for each plan were recalculated after individually modifying parameters of interest (e.g., MLC transmission, percent depth doses [PDDs], and output factors) according to the 2.5th to 97.5 percentiles of community survey and machine performance data to encompass the realistic extent of variance in the radiotherapy community. The resultant dose distributions were evaluated by examining relative changes in average dose for thermoluminescent dosimeter (TLD) locations across the two target volumes and organ at risk (OAR). Interplay was also examined for parameters generating changes in target dose greater than 1%.

Results: For Eclipse, dose calculations were sensitive to changes in the dosimetric leaf gap (DLG), which resulted in differences from -5% to +3% to the targets relative to the baseline beam model. Modifying the MLC transmission factor introduced differences up to ± 1%. For RayStation, parameters determining MLC behaviors likewise contributed substantially; the MLC offset introduced changes in dose from -4% to +7%, and the MLC transmission caused changes of -4% to +2%. Among the dosimetric qualities examined, changes in PDD implementation resulted in the most substantial changes, but these were only up to ±1%. Other dosimetric factors had <1% impact on dose accuracy. Interplay between impactful parameters was found to be minimal.

Conclusion: Factors related to the modeling of the MLC, particularly relating to the leaf offset, can cause clinically significant changes in the calculated dose for IMRT and VMAT plans. This should be of concern to the radiotherapy community because the clinical effects of poor TPS commissioning were based on reported data from clinically implemented beam models. These results further reinforce that dose errors caused by poor TPS calculations are often involved in IROC phantom failures.
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http://dx.doi.org/10.1002/mp.14396DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7689833PMC
October 2020

Dose calculation errors as a component of failing IROC lung and spine phantom irradiations.

Med Phys 2020 Sep 23;47(9):4502-4508. Epub 2020 Jun 23.

The University of Texas MD Anderson Cancer Center UT Health Graduate School of Biomedical Sciences, Houston, TX, 77030, USA.

Purpose: Between July 2013 and August 2019, 22% of the imaging and radiation oncology core (IROC) spine, and 15% of the moving lung phantom irradiations have failed to meet established acceptability criteria. The spine phantom simulates a highly modulated stereotactic body radiation therapy (SBRT) case, whereas the lung phantom represents a low-to-none modulation moving target case. In this study, we assessed the contribution of dose calculation errors to these phantom results and evaluated their effects on failure rates.

Methods: We evaluated dose calculation errors by comparing the calculation accuracy of various institutions' treatment planning systems (TPSs) vs IROC-Houston's previously established independent dose recalculation system (DRS). Each calculation was compared with the measured dose actually delivered to the phantom; cases in which the recalculation was more accurate were interpreted as a deficiency in the institution's TPS. A total of 258 phantom irradiation plans (172 lung and 86 spine) were recomputed.

Results: Overall, the DRS performed better than the TPSs in 47% of the spine phantom cases. However, the DRS was more accurate in 93% of failing spine phantom cases (with an average improvement of 2.35%), indicating a deficiency in the institution's treatment planning system. Deficiencies in dose calculation accounted for 60% of the overall discrepancy between measured and planned doses among spine phantoms. In contrast, lung phantom DRS calculations were more accurate in only 35% and 42% of all and failing lung phantom cases respectively, indicating that dose calculation errors were not substantially present. These errors accounted for only 30% of the overall discrepancy between measured and planned doses.

Conclusions: Dose calculation errors are common and substantial in IROC spine phantom irradiations, highlighting a major failure mode in this phantom and in clinical treatment management of these cases. In contrast, dose calculation accuracy had only a minimal contribution to failing lung phantom results, indicating that other failure modes drive problems with this phantom and similar clinical treatments.
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http://dx.doi.org/10.1002/mp.14258DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7686159PMC
September 2020

Differences in the Patterns of Failure Between IROC Lung and Spine Phantom Irradiations.

Pract Radiat Oncol 2020 Sep - Oct;10(5):372-381. Epub 2020 May 13.

UT Health Graduate School of Biomedical Sciences, Houston, Texas; IROC Houston Quality Assurance Center, Houston, Texas; Department of Radiation Physics, Houston, Texas. Electronic address:

Purpose: Our purpose was to investigate and classify the reasons why institutions fail the Imaging and Radiation Oncology Core (IROC) stereotactic body radiation therapy (SBRT) spine and moving lung phantoms, which are used to credential institutions for clinical trial participation.

Methods And Materials: All IROC moving lung and SBRT spine phantom irradiation failures recorded from January 2012 to December 2018 were evaluated in this study. A failure was a case where the institution did not meet the established IROC criteria for agreement between planned and delivered dose. We analyzed the reports for all failing irradiations, including point dose disagreement, dose profiles, and gamma analyses. Classes of failure patterns were created and used to categorize each instance.

Results: There were 158 failing cases analyzed: 116 of 1052 total lung irradiations and 42 of 263 total spine irradiations. Seven categories were required to describe the lung phantom failures, whereas 4 were required for the spine. Types of errors present in both phantom groups included systematic dose and localization errors. Fifty percent of lung failures were due to a superior-inferior localization error, that is, error in the direction of major motion. Systematic dose errors, however, contributed to only 22% of lung failures. In contrast, the majority (60%) of spine phantom failures were due to systematic dose errors, with localization errors (in any direction) accounting for only 14% of failures.

Conclusions: There were 2 distinct patterns of failure between the IROC moving lung and SBRT spine phantoms. The majority of the lung phantom failures were due to localization errors, whereas the spine phantom failures were largely attributed to systematic dose errors. Both of these errors are clinically relevant and could manifest as errors in patient cases. These findings highlight the value of independent end-to-end dosimetry audits and can help guide the community in improving the quality of radiation therapy by focusing attention on where errors manifest in the community.
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http://dx.doi.org/10.1016/j.prro.2020.04.004DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7483400PMC
August 2021

Survey results of 3D-CRT and IMRT quality assurance practice.

J Appl Clin Med Phys 2020 Jul 30;21(7):70-76. Epub 2020 Apr 30.

Imaging and Radiation Core Houston QA Center, Houston, TX, USA.

Purpose: To create a snapshot of common practices for 3D-CRT and intensity-modulated radiation therapy (IMRT) QA through a large-scale survey and compare to TG-218 recommendations.

Methods: A survey of 3D-CRT and IMRT QA was constructed at and distributed by the IROC-Houston QA center to all institutions monitored by IROC (n = 2,861). The first part of the survey asked about methods to check dose delivery for 3D-CRT. The bulk of the survey focused on IMRT QA, inquiring about treatment modalities, standard tools used to verify planned dose, how assessment of agreement is calculated and the comparison criteria used, and the strategies taken if QA fails.

Results: The most common tools for dose verification were a 2D diode array (52.8%), point(s) measurement (39.0%), EPID (27.4%), and 2D ion chamber array (23.9%). When IMRT QA failed, the highest average rank strategy utilized was to remeasure with the same setup, which had an average position ranking of 1.1 with 90.4% of facilities employing this strategy. The second highest average ranked strategy was to move to a new calculation point and remeasure (54.9%); this had an average ranking of 2.1.

Conclusion: The survey provided a snapshot of the current state of dose verification for IMRT radiotherapy. The results showed variability in approaches and that work is still needed to unify and tighten criteria in the medical physics community, especially in reference to TG-218's recommendations.
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http://dx.doi.org/10.1002/acm2.12885DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7386182PMC
July 2020

A Mail Audit Independent Peer Review System for Dosimetry Verification of a Small Animal Irradiator.

Radiat Res 2020 04 18;193(4):341-350. Epub 2020 Feb 18.

Departments of Radiation Physics.

Dedicated precision orthovoltage small animal irradiators have become widely available in the past decade and are commonly used for radiation biology research. However, there is a lack of dosimetric standardization among these irradiators, which affects the reproducibility of radiation-based animal studies. The purpose of this study was to develop a mail-based, independent peer review system to verify dose delivery among institutions using X-RAD 225Cx irradiators (Precision X-Ray, North Branford, CT). A robust, user-friendly mouse phantom was constructed from high-impact polystyrene and designed with dimensions similar to those of a typical laboratory mouse. The phantom accommodates three thermoluminescent dosimeters (TLDs) to measure dose. The mouse peer review system was commissioned in a small animal irradiator using anterior-posterior and posterior-anterior beams of 225 kVp and then mailed to three institutions to test the feasibility of the audit service. The energy correction factor for TLDs in the mouse phantom was derived to validate the delivered dose using this particular animal irradiation system. This feasibility study indicated that three institutions were able to deliver a radiation dose to the mouse phantom within ±10% of the target dose. The developed mail audit independent peer review system for the verification of mouse dosimetry can be expanded to characterize other commercially available orthovoltage irradiators, thereby enhancing the reproducibility of studies employing these irradiators.
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http://dx.doi.org/10.1667/RR15220.1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8177689PMC
April 2020

Reference dataset of users' photon beam modeling parameters for the Eclipse, Pinnacle, and RayStation treatment planning systems.

Med Phys 2020 Jan 15;47(1):282-288. Epub 2019 Nov 15.

Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, TX, 77030, USA.

Purpose: The aim of this work was to provide a novel description of how the radiotherapy community configures treatment planning system (TPS) radiation beam models for clinically used treatment machines. Here we describe the results of a survey of self-reported TPS beam modeling parameter values across different C-arm linear accelerators, beam energies, and multileaf collimator (MLC) configurations.

Acquisition And Validation Methods: Beam modeling data were acquired via electronic survey implemented through the Imaging and Radiation Oncology Core (IROC) Houston Quality Assurance Center's online facility questionnaire. The survey was open to participation from January 2018 through January 2019 for all institutions monitored by IROC. After quality control, 2818 beam models were collected from 642 institutions. This survey, designed for Eclipse, Pinnacle, and RayStation, instructed physicists to report parameter values used to model the radiation source and MLC for each treatment machine and beam energy used clinically for intensity-modulated radiation therapy. Parameters collected included the effective source/spot size, MLC transmission, dosimetric leaf gap, tongue and groove effect, and other nondosimetric parameters specific to each TPS. To facilitate survey participation, instructions were provided on how to identify requested beam modeling parameters within each TPS environment.

Data Format And Usage Notes: Numeric values of the beam modeling parameters are compiled and tabulated according to TPS and calculation algorithm, linear accelerator model class, beam energy, and MLC configuration. Values are also presented as distributions, ranging from the 2.5th to the 97.5th percentile.

Potential Applications: These data provide an independent guide describing how the radiotherapy community mathematically represents its clinical radiation beams. These distributions may be used by the community for comparison during the commissioning or verification of their TPS beam models. Ultimately, we hope that the current work will allow institutions to spot potentially suspicious parameter values and help ensure more accurate radiotherapy delivery.
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http://dx.doi.org/10.1002/mp.13892DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6980266PMC
January 2020

Testing the methodology for a dosimetric end-to-end audit of IMRT/VMAT: results of IAEA multicentre and national studies.

Acta Oncol 2019 Dec 19;58(12):1731-1739. Epub 2019 Aug 19.

International Atomic Energy Agency, Vienna, Austria.

Within an International Atomic Energy Agency (IAEA) co-ordinated research project (CRP), a remote end-to-end dosimetric quality audit for intensity modulated radiation therapy (IMRT)/ volumetric arc therapy (VMAT) was developed to verify the radiotherapy chain including imaging, treatment planning and dose delivery. The methodology as well as the results obtained in a multicentre pilot study and national trial runs conducted in close cooperation with dosimetry audit networks (DANs) of IAEA Member States are presented. A solid polystyrene phantom containing a dosimetry insert with an irregular solid water planning target volume (PTV) and organ at risk (OAR) was designed for this audit. The insert can be preloaded with radiochromic film and four thermoluminescent dosimeters (TLDs). For the audit, radiotherapy centres were asked to scan the phantom, contour the structures, create an IMRT/VMAT treatment plan and irradiate the phantom. The dose prescription was to deliver 4 Gy to the PTV in two fractions and to limit the OAR dose to a maximum of 2.8 Gy. The TLD measured doses and film measured dose distributions were compared with the TPS calculations. Sixteen hospitals from 13 countries and 64 hospitals from 6 countries participated in the multicenter pilot study and in the national runs, respectively. The TLD results for the PTV were all within ±5% acceptance limit for the multicentre pilot study, whereas for national runs, 17 participants failed to meet this criterion. All measured doses in the OAR were below the treatment planning constraint. The film analysis identified seven plans in national runs below the 90% passing rate gamma criteria. The results proved that the methodology of the IMRT/VMAT dosimetric end-to-end audit was feasible for its intended purpose, i.e., the phantom design and materials were suitable; the phantom was easy to use and it was robust enough for shipment. Most importantly the audit methodology was capable of identifying suboptimal IMRT/VMAT delivery.
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http://dx.doi.org/10.1080/0284186X.2019.1648859DOI Listing
December 2019

Independent recalculation outperforms traditional measurement-based IMRT QA methods in detecting unacceptable plans.

Med Phys 2019 Aug 23;46(8):3700-3708. Epub 2019 Jun 23.

Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Blvd, Houston, TX, 7030, USA.

Purpose: To evaluate the performance of an independent recalculation and compare it against current measurement-based patient specific intensity-modulated radiation therapy (IMRT) quality assurance (QA) in predicting unacceptable phantom results as measured by the Imaging and Radiation Oncology Core (IROC).

Methods: When institutions irradiate the IROC head and neck IMRT phantom, they are also asked to submit their internal IMRT QA results. Separately from this, IROC has previously created reference beam models on the Mobius3D platform to independently recalculate phantom results based on the institution's DICOM plan data. The ability of the institutions' IMRT QA to predict the IROC phantom result was compared against the independent recalculation for 339 phantom results collected since 2012. This was done to determine the ability of these systems to detect failing phantom results (i.e., large errors) as well as poor phantom results (i.e., modest errors). Sensitivity and specificity were evaluated using common clinical thresholds, and receiver operator characteristic (ROC) curves were used to compare across different thresholds.

Results: Overall, based on common clinical criteria, the independent recalculation was 12 times more sensitive at detecting unacceptable (failing) IROC phantom results than clinical measurement-based IMRT QA. The recalculation was superior, in head-to-head comparison, to the EPID, ArcCheck, and MapCheck devices. The superiority of the recalculation vs these array-based measurements persisted under ROC analysis as the recalculation curve had a greater area under it and was always above that for these measurement devices. For detecting modest errors (poor phantom results rather than failing phantom results), neither the recalculation nor measurement-based IMRT QA performed well.

Conclusions: A simple recalculation outperformed current measurement-based IMRT QA methods at detecting unacceptable plans. These findings highlight the value of an independent recalculation, and raise further questions about the current standard of measurement-based IMRT QA.
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http://dx.doi.org/10.1002/mp.13638DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6692191PMC
August 2019

Higher Reported Lung Dose Received During Total Body Irradiation for Allogeneic Hematopoietic Stem Cell Transplantation in Children With Acute Lymphoblastic Leukemia Is Associated With Inferior Survival: A Report from the Children's Oncology Group.

Int J Radiat Oncol Biol Phys 2019 07 23;104(3):513-521. Epub 2019 Feb 23.

Children's Center for Cancer and Blood Diseases, Children's Hospital Los Angeles, University of Southern California Keck School of Medicine, Los Angeles, California.

Purpose: To examine the relationship between lung radiation dose and survival outcomes in children undergoing total body irradiation (TBI)-based hematopoietic stem cell transplantation (HSCT) for acute lymphoblastic leukemia on the Children's Oncology Group trial.

Methods And Materials: TBI (1200 or 1320 cGy given twice daily in 6 or 8 fractions) was used as part of 3 HSCT preparative regimens, allowing institutional flexibility regarding TBI techniques, including lung shielding. Lung doses as reported by each participating institution were calculated for different patient setups, with and without shielding, with a variety of dose calculation techniques. The association between lung dose and transplant-related mortality, relapse-free survival, and overall survival (OS) was examined using the Cox proportional hazards regression model controlling for the following variables: TBI dose rate, TBI fields, patient position during TBI, donor type, and pre-HSCT minimal residual disease level.

Results: Of a total of 143 eligible patients, 127 had lung doses available for this analysis. The TBI techniques were heterogeneous. The mean lung dose was reported as 904.5 cGy (standard deviation, ±232.3). Patients treated with lateral fields were more likely to receive lung doses ≥800 cGy (P < .001). The influence of lung dose ≥800 cGy on transplant-related mortality was not significant (hazard ratio [HR], 1.78; P = .21). On univariate analysis, lung dose ≥800 cGy was associated with inferior relapse-free survival (HR, 1.76; P = .04) and OS (HR, 1.85; P = .03). In the multivariate analysis, OS maintained statistical significance (HR, 1.85; P = .04).

Conclusions: The variability in TBI techniques resulted in uncertainty with reported lung doses. Lateral fields were associated with higher lung dose, and thus they should be avoided. Patients treated with lung dose <800 cGy in this study had better outcomes. This approach is currently being investigated in the Children's Oncology Group AALL1331 study. Additionally, the Imaging and Radiation Oncology Core Group is evaluating effects of TBI techniques on lung doses using a phantom.
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http://dx.doi.org/10.1016/j.ijrobp.2019.02.034DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6548591PMC
July 2019

Radiation-induced lung toxicity in mice irradiated in a strong magnetic field.

PLoS One 2018 16;13(11):e0205803. Epub 2018 Nov 16.

Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas, United States of America.

Strong magnetic fields affect radiation dose deposition in MRI-guided radiation therapy systems, particularly at interfaces between tissues of differing densities such as those in the thorax. In this study, we evaluated the impact of a 1.5 T magnetic field on radiation-induced lung damage in C57L/J mice. We irradiated 140 mice to the whole thorax with parallel-opposed Co-60 beams to doses of 0, 9.0, 10.0, 10.5, 11.0, 12.0, or 13.0 Gy (20 mice per dose group). Ten mice per dose group were irradiated while a 1.5 T magnetic field was applied transverse to the radiation beam and ten mice were irradiated with the magnetic field set to 0 T. We compared survival and noninvasive assays of radiation-induced lung damage, namely respiratory rate and metrics derived from thoracic cone-beam CTs, between the two sets of mice. We report two main results. First, the presence of a transverse 1.5 T field during irradiation had no impact on survival of C57L/J mice. Second, there was a small but statistically significant effect on noninvasive assays of radiation-induced lung damage. These results provide critical safety data for the clinical introduction of MRI-guided radiation therapy systems.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0205803PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6239291PMC
April 2019

The Importance of Imaging in Radiation Oncology for National Clinical Trials Network Protocols.

Int J Radiat Oncol Biol Phys 2018 11 18;102(4):775-782. Epub 2018 Oct 18.

Imaging and Radiation Oncology Core QA Center Rhode Island, University of Massachusetts Medical School, Lincoln, Rhode Island.

Imaging is essential in successfully executing radiation therapy (RT) in oncology clinical trials. As technically sophisticated diagnostic imaging and RT were incorporated into trials, quality assurance in the National Clinical Trials Network groups entered a new era promoting image acquisition and review. Most trials involving RT require pre- and post-therapy imaging for target validation and outcome assessment. The increasing real-time (before and during therapy) imaging and RT object reviews are to ensure compliance with trial objectives. Objects easily transmit digitally for review from anywhere in the world. Physician interpretation of imaging and image application to RT treatment plans is essential for optimal trial execution. Imaging and RT data sets are used to credential RT sites to confirm investigator and institutional ability to meet trial target volume delineation and delivery requirements. Real-time imaging and RT object reviews can be performed multiple times during a trial to assess response to therapy and application of RT objects. This process has matured into an effective data management mechanism. When necessary, site and study investigators review objects together through web media technologies to ensure the patient is enrolled on the appropriate trial and the intended RT is planned and executed in a trial-compliant manner. Real-time imaging review makes sure: (1) the patient is entered and eligible for the trial, (2) the patient meets trial-specific adaptive therapy requirements, if applicable, and (3) the intended RT is according to trial guidelines. This review ensures the study population is uniform and the results are believable and can be applied to clinical practice.
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http://dx.doi.org/10.1016/j.ijrobp.2018.08.039DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6510266PMC
November 2018

Treatment plan complexity does not predict IROC Houston anthropomorphic head and neck phantom performance.

Phys Med Biol 2018 10 17;63(20):205015. Epub 2018 Oct 17.

The University of Texas MD Anderson Cancer Center, UTHealth Graduate School of Biomedical Sciences, Houston, TX 77030, United States of America. Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, United States of America.

Previous works indicate that intensity-modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) plans that are highly complex may produce more errors in dose calculation and treatment delivery. Multiple complexity metrics have been proposed and associated with IMRT QA results, but their relationships with plan performance using in situ dose measurements have not been thoroughly investigated. This study aimed to evaluate the relationships between IMRT treatment plan complexity and anthropomorphic phantom performance in order to assess the extent to which plan complexity is related to dosimetric performance in the IROC phantom credentialing program. Sixteen complexity metrics, including the modulation complexity score (MCS), several modulation indices, and total monitor units (MU) delivered, were evaluated for 343 head and neck phantom irradiations, comprising both IMRT (step-and-shoot and sliding window techniques) and VMAT. Spearman's correlations were used to explore the relationship between complexity and plan performance, as measured by the dosimetric differences between the treatment planning system (TPS) and thermoluminescent dosimeter (TLD) measurement, as well as film gamma analysis. Relationships were likewise determined for several combinations of subpopulations, based on the linear accelerator model, TPS used, and delivery modality. Evaluation of the complexity metrics presented here yielded no significant relationships (p  >  0.01, Bonferroni-corrected) and all correlations were weak (less than  ±0.30). These results indicate that complexity metrics have limited predictive utility in assessing plan performance in multi-institutional comparisons of IMRT plans. Other factors affecting plan accuracy, such as dosimetric modeling or multileaf collimator (MLC) performance, should be investigated to determine a more probable cause for dose delivery errors.
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http://dx.doi.org/10.1088/1361-6560/aae29eDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6287268PMC
October 2018

A New Anthropomorphic Pediatric Spine Phantom for Proton Therapy Clinical Trial Credentialing.

Int J Part Ther 2018 26;4(4):20-27. Epub 2018 Jul 26.

Imaging and Radiation Oncology Core Quality Assurance Office, Houston, TX, USA.

Purpose: To design and evaluate an anthropomorphic spine phantom for use in credentialing proton therapy facilities for clinical trial participation by the Imaging and Radiation Oncology Core Houston QA Center.

Materials And Methods: A phantom was designed to perform an end-to-end audit of the proton spine treatment process, including simulation, dose calculation, and proton treatment delivery. Because plastics that simulate bone in proton beams are unknown, 11 potential materials were tested to identify suitable phantom materials. Once built, preliminary testing using passive scattering and spot scanning treatment plans (including a field junction) were created in-house and delivered 3 times to test reproducibility. The following measured attributes were compared with the calculated values: absolute dose agreement using thermoluminescent dosimeters, planar gamma agreement, distal range, junction match, and right and left profile alignment using radiochromic film. Finally, credentialing results from 10 institutions were also assessed.

Results: A suitable bone substitute was identified (Techtron HPV Bearing Grade), which had a measured relative stopping power that agreed within 1.1% of its value calculated by Eclipse. In-house passive scatter testing of the phantom demonstrated that the phantom was suitable for assessing craniospinal irradiation dose delivery. However, the in-house scanning beam results were more mixed, highlighting challenges in treatment delivery. Seven of ten institutions passed the proposed criteria for this phantom, a pass rate consistent with other Imaging and Radiation Oncology phantoms.

Conclusions: An anthropomorphic proton spine phantom was developed to evaluate proton therapy delivery. This phantom provides a realistic challenge for centers wishing to participate in proton clinical trials and highlights the need for caution in applying advanced treatments.
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http://dx.doi.org/10.14338/IJPT-17-00024.1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6132268PMC
July 2018

Cardiac-Sparing Whole Lung IMRT in Patients With Pediatric Tumors and Lung Metastasis: Final Report of a Prospective Multicenter Clinical Trial.

Int J Radiat Oncol Biol Phys 2019 01 29;103(1):28-37. Epub 2018 Aug 29.

Imaging and Radiation Oncology Core, Providence, Rhode Island.

Purpose: A prospective clinical trial was conducted for patients undergoing cardiac sparing (CS) whole lung irradiation (WLI) using intensity modulated radiation therapy (IMRT). The 3 trial aims were (1) to demonstrate the feasibility of CS IMRT with real-time central quality control; (2) to determine the dosimetric advantages of WLI using IMRT compared with standard anteroposterior (AP) techniques; and (3) to determine acute tolerance and short-term efficacy after a protocol-mandated minimum 2-year follow-up for all patients.

Methods And Materials: All patients underwent a 3-dimensional chest computed tomography scan and a contrast-enhanced 4-dimensional (4D) gated chest computed tomography scan using a standard gating device. The clinical target volume was the entire bilateral 3-dimensional lung volume, and the internal target volume was the 4D minimum intensity projection of both lungs. The internal target volume was expanded by 1 cm to get the planning target volume. All target volumes, cardiac contours, and treatment plans were centrally reviewed before treatment. The different cardiac volumes receiving percentages of prescribed radiation therapy (RT) doses on AP and IMRT WLI plans were estimated and compared.

Results: The target 20 patients were accrued in 2 years. Median RT dose was 15 Gy. Real-time central quality assurance review and plan preapproval were obtained for all patients. WLI using IMRT was feasible in all patients. Compared with standard AP WLI, CS IMRT resulted in a statistically significant reduction in radiation doses to the whole heart, atria, ventricles, and coronaries. One child developed cardiac dysfunction and pulmonary restrictive disease 5.5 years after CS IMRT (15 Gy) and doxorubicin (375 mg/m). The 2- and 3-year lung metastasis progression-free survival was 65% and 52%, respectively.

Conclusions: We have demonstrated the feasibility of WLI using CS IMRT and confirmed the previously reported advantages of IMRT, including superior cardiac protection and superior dose coverage of 4D lung volumes. Further studies are required to establish the efficacy and safety of this irradiation technique.
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http://dx.doi.org/10.1016/j.ijrobp.2018.08.034DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6391051PMC
January 2019

Retrospective Validation and Clinical Implementation of Automated Contouring of Organs at Risk in the Head and Neck: A Step Toward Automated Radiation Treatment Planning for Low- and Middle-Income Countries.

J Glob Oncol 2018 07;4:1-11

Rachel E. McCarroll, Peter A. Balter, Carlos E. Cardenas, David S. Followill, Kelly D. Kisling, Christopher L. Nelson, Christine B. Peterson, Lifei Zhang, Laurence E. Court, and Jinzhong Yang, The University of Texas MD Anderson Cancer Center, Houston, TX; Beth M. Beadle, Stanford University, Stanford, CA; Hester Burger, Sameera Dalvie, and Julie Wetter, Groote Schuur Hospital and University of Cape Town; Komeela Naidoo, Stellenbosch University and Tygerberg Hospital, Cape Town; Karin Vorster, University of the Free State, Bloemfontein, South Africa; and Michael Mejia, University of Santo Tomas Hospital, Benavides Cancer Institute, Manila, Philippines.

Purpose We assessed automated contouring of normal structures for patients with head-and-neck cancer (HNC) using a multiatlas deformable-image-registration algorithm to better provide a fully automated radiation treatment planning solution for low- and middle-income countries, provide quantitative analysis, and determine acceptability worldwide. Methods Autocontours of eight normal structures (brain, brainstem, cochleae, eyes, lungs, mandible, parotid glands, and spinal cord) from 128 patients with HNC were retrospectively scored by a dedicated HNC radiation oncologist. Contours from a 10-patient subset were evaluated by five additional radiation oncologists from international partner institutions, and interphysician variability was assessed. Quantitative agreement of autocontours with independently physician-drawn structures was assessed using the Dice similarity coefficient and mean surface and Hausdorff distances. Automated contouring was then implemented clinically and has been used for 166 patients, and contours were quantitatively compared with the physician-edited autocontours using the same metrics. Results Retrospectively, 87% of normal structure contours were rated as acceptable for use in dose-volume-histogram-based planning without edit. Upon clinical implementation, 50% of contours were not edited for use in treatment planning. The mean (± standard deviation) Dice similarity coefficient of autocontours compared with physician-edited autocontours for parotid glands (0.92 ± 0.10), brainstem (0.95 ± 0.09), and spinal cord (0.92 ± 0.12) indicate that only minor edits were performed. The average mean surface and Hausdorff distances for all structures were less than 0.15 mm and 1.8 mm, respectively. Conclusion Automated contouring of normal structures generates reliable contours that require only minimal editing, as judged by retrospective ratings from multiple international centers and clinical integration. Autocontours are acceptable for treatment planning with no or, at most, minor edits, suggesting that automated contouring is feasible for clinical use and in the ongoing development of automated radiation treatment planning algorithms.
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http://dx.doi.org/10.1200/JGO.18.00055DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6223488PMC
July 2018

Reference dosimetry data and modeling challenges for Elekta accelerators based on IROC-Houston site visit data.

Med Phys 2018 May 1;45(5):2337-2344. Epub 2018 Apr 1.

Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, TX, 77030, USA.

Purpose: Reference dosimetry data can provide an independent second check of acquired values when commissioning or validating a treatment planning system (TPS). The Imaging and Radiation Oncology Core at Houston (IROC-Houston) has measured numerous linear accelerators throughout its existence. The results of those measurements are given here, comparing accelerators and the agreement of measurement versus institutional TPS calculations.

Methods: Data from IROC-Houston on-site reviews from 2000 through 2014 were analyzed for all Elekta accelerators, approximately 50. For each, consistent point dose measurements were conducted for several basic parameters in a water phantom, including percentage depth dose, output factors, small-field output factors, off-axis factors, and wedge factors. The results were compared by accelerator type independently for 6, 10, 15, and 18 MV. Distributions of the measurements for each parameter are given, providing the mean and standard deviation. Each accelerator's measurements were also compared to its corresponding TPS calculation from the institution to determine the level of agreement, as well as determining which dosimetric parameters were most often in error.

Results: Accelerators were grouped by head type and reference dosimetric values were compiled. No class of linac had better overall agreement with its TPS, but percentage depth dose and output factors commonly agreed well, while small-field output factors, off-axis factors, and wedge factors often disagreed substantially from their TPS calculations.

Conclusion: Reference data has been collected and analyzed for numerous Elekta linacs, which provide an independent way for a physicist to double-check their own measurements to prevent gross treatment errors. In addition, treatment planning parameters more often in error have been highlighted, providing practical caution for physicists commissioning treatment planning systems for Elekta linacs.
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http://dx.doi.org/10.1002/mp.12865DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6592280PMC
May 2018

A multinational audit of small field output factors calculated by treatment planning systems used in radiotherapy.

Phys Imaging Radiat Oncol 2018 Jan 6;5:58-63. Epub 2018 Mar 6.

International Atomic Energy Agency, Vienna, Austria.

Background And Purpose: An audit methodology for verifying the implementation of output factors (OFs) of small fields in treatment planning systems (TPSs) used in radiotherapy was developed and tested through a multinational research group and performed on a national level in five different countries.

Materials And Methods: Centres participating in this study were asked to provide OFs calculated by their TPSs for 10 × 10 cm, 6 × 6 cm, 4 × 4 cm, 3 × 3 cm and 2 × 2 cm field sizes using an SSD of 100 cm. The ratio of these calculated OFs to reference OFs was analysed. The action limit was ±3% for the 2 × 2 cm field and ±2% for all other fields.

Results: OFs for more than 200 different beams were collected in total. On average, the OFs for small fields calculated by TPSs were generally larger than measured reference data. These deviations increased with decreasing field size. On a national level, 30% and 31% of the calculated OFs of the 2 × 2 cm field exceeded the action limit of 3% for nominal beam energies of 6 MV and for nominal beam energies higher than 6 MV, respectively.

Conclusion: Modern TPS beam models generally overestimate the OFs for small fields. The verification of calculated small field OFs is a vital step and should be included when commissioning a TPS. The methodology outlined in this study can be used to identify potential discrepancies in clinical beam models.
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http://dx.doi.org/10.1016/j.phro.2018.02.005DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7807586PMC
January 2018

Radiation Therapy Deficiencies Identified During On-Site Dosimetry Visits by the Imaging and Radiation Oncology Core Houston Quality Assurance Center.

Int J Radiat Oncol Biol Phys 2017 12 24;99(5):1094-1100. Epub 2017 Aug 24.

Imaging and Radiation Oncology Core Quality Assurance Center in Houston, Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas; The University of Texas Health Science Center Houston, Graduate School of Biomedical Sciences, Houston, Texas.

Purpose: To review the dosimetric, mechanical, and programmatic deficiencies most frequently observed during on-site visits of radiation therapy facilities by the Imaging and Radiation Oncology Core Quality Assurance Center in Houston (IROC Houston).

Methods And Materials: The findings of IROC Houston between 2000 and 2014, including 409 institutions and 1020 linear accelerators (linacs), were compiled. On-site evaluations by IROC Houston include verification of absolute calibration (tolerance of ±3%), relative dosimetric review (tolerances of ±2% between treatment planning system [TPS] calculation and measurement), mechanical evaluation (including multileaf collimator and kilovoltage-megavoltage isocenter evaluation against Task Group [TG]-142 tolerances), and general programmatic review (including institutional quality assurance program vs TG-40 and TG-142).

Results: An average of 3.1 deficiencies was identified at each institution visited, a number that has decreased slightly with time. The most common errors are tabulated and include TG-40/TG-142 compliance (82% of institutions were deficient), small field size output factors (59% of institutions had errors ≥3%), and wedge factors (33% of institutions had errors ≥3%). Dosimetric errors of ≥10%, including in beam calibration, were seen at many institutions.

Conclusions: There is substantial room for improvement of both dosimetric and programmatic issues in radiation therapy, which should be a high priority for the medical physics community. Particularly relevant was suboptimal beam modeling in the TPS and a corresponding failure to detect these errors by not including TPS data in the linac quality assurance process.
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http://dx.doi.org/10.1016/j.ijrobp.2017.08.013DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5699963PMC
December 2017

An FMEA evaluation of intensity modulated radiation therapy dose delivery failures at tolerance criteria levels.

Med Phys 2017 Nov 19;44(11):5575-5583. Epub 2017 Oct 19.

IROC Houston QA Center, The University of Texas MD Anderson Cancer Center, Houston, TX, 77030, USA.

Purpose: The objective of this work was to assess both the perception of failure modes in Intensity Modulated Radiation Therapy (IMRT) when the linac is operated at the edge of tolerances given in AAPM TG-40 (Kutcher et al.) and TG-142 (Klein et al.) as well as the application of FMEA to this specific section of the IMRT process.

Methods: An online survey was distributed to approximately 2000 physicists worldwide that participate in quality services provided by the Imaging and Radiation Oncology Core - Houston (IROC-H). The survey briefly described eleven different failure modes covered by basic quality assurance in step-and-shoot IMRT at or near TG-40 (Kutcher et al.) and TG-142 (Klein et al.) tolerance criteria levels. Respondents were asked to estimate the worst case scenario percent dose error that could be caused by each of these failure modes in a head and neck patient as well as the FMEA scores: Occurrence, Detectability, and Severity. Risk probability number (RPN) scores were calculated as the product of these scores. Demographic data were also collected.

Results: A total of 181 individual and three group responses were submitted. 84% were from North America. Most (76%) individual respondents performed at least 80% clinical work and 92% were nationally certified. Respondent medical physics experience ranged from 2.5 to 45 yr (average 18 yr). A total of 52% of individual respondents were at least somewhat familiar with FMEA, while 17% were not familiar. Several IMRT techniques, treatment planning systems, and linear accelerator manufacturers were represented. All failure modes received widely varying scores ranging from 1 to 10 for occurrence, at least 1-9 for detectability, and at least 1-7 for severity. Ranking failure modes by RPN scores also resulted in large variability, with each failure mode being ranked both most risky (1st) and least risky (11th) by different respondents. On average MLC modeling had the highest RPN scores. Individual estimated percent dose errors and severity scores positively correlated (P < 0.01) for each FM as expected. No universal correlations were found between the demographic information collected and scoring, percent dose errors or ranking.

Conclusions: Failure modes investigated overall were evaluated as low to medium risk, with average RPNs less than 110. The ranking of 11 failure modes was not agreed upon by the community. Large variability in FMEA scoring may be caused by individual interpretation and/or experience, reflecting the subjective nature of the FMEA tool.
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http://dx.doi.org/10.1002/mp.12551DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6421844PMC
November 2017

Pencil Beam Algorithms Are Unsuitable for Proton Dose Calculations in Lung.

Int J Radiat Oncol Biol Phys 2017 11 13;99(3):750-756. Epub 2017 Jun 13.

The Imaging and Radiation Oncology Core Houston Quality Assurance Center, The University of Texas MD Anderson Cancer Center, Houston, Texas.

Purpose: To compare analytic and Monte Carlo-based algorithms for proton dose calculations in the lung, benchmarked against anthropomorphic lung phantom measurements.

Methods And Materials: A heterogeneous anthropomorphic moving lung phantom has been irradiated at numerous proton therapy centers. At 5 centers the treatment plan could be calculated with both an analytic and Monte Carlo algorithm. The doses calculated in the treatment plans were compared with the doses delivered to the phantoms, which were measured using thermoluminescent dosimeters and film. Point doses were compared, as were planar doses using a gamma analysis.

Results: The analytic algorithms overestimated the dose to the center of the target by an average of 7.2%, whereas the Monte Carlo algorithms were within 1.6% of the physical measurements on average. In some regions of the target volume, the analytic algorithm calculations differed from the measurement by up to 31% in the internal gross target volume (iGTV) (46% in the planning target volume), over-predicting the dose. All comparisons showed a region of at least 15% dose discrepancy within the iGTV between the analytic calculation and the measured dose. The Monte Carlo algorithm recalculations showed dramatically improved agreement with the measured doses, showing mean agreement within 4% for all cases and a maximum difference of 12% within the iGTV.

Conclusions: Analytic algorithms often do a poor job predicting proton dose in lung tumors, over-predicting the dose to the target by up to 46%, and should not be used unless extensive validation counters the consistent results of the present study. Monte Carlo algorithms showed dramatically improved agreement with physical measurements and should be implemented to better reflect actual delivered dose distributions.
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http://dx.doi.org/10.1016/j.ijrobp.2017.06.003DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5729062PMC
November 2017

Treatment Planning System Calculation Errors Are Present in Most Imaging and Radiation Oncology Core-Houston Phantom Failures.

Int J Radiat Oncol Biol Phys 2017 08 4;98(5):1197-1203. Epub 2017 Apr 4.

Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas; Imaging and Radiation Oncology Core-Houston, The University of Texas MD Anderson Cancer Center, Houston, Texas; Graduate School of Biomedical Sciences, The University of Texas Health Science Center-Houston, Houston, Texas. Electronic address:

Purpose: The anthropomorphic phantom program at the Houston branch of the Imaging and Radiation Oncology Core (IROC-Houston) is an end-to-end test that can be used to determine whether an institution can accurately model, calculate, and deliver an intensity modulated radiation therapy dose distribution. Currently, institutions that do not meet IROC-Houston's criteria have no specific information with which to identify and correct problems. In the present study, an independent recalculation system was developed to identify treatment planning system (TPS) calculation errors.

Methods And Materials: A recalculation system was commissioned and customized using IROC-Houston measurement reference dosimetry data for common linear accelerator classes. Using this system, 259 head and neck phantom irradiations were recalculated. Both the recalculation and the institution's TPS calculation were compared with the delivered dose that was measured. In cases in which the recalculation was statistically more accurate by 2% on average or 3% at a single measurement location than was the institution's TPS, the irradiation was flagged as having a "considerable" institutional calculation error. The error rates were also examined according to the linear accelerator vendor and delivery technique.

Results: Surprisingly, on average, the reference recalculation system had better accuracy than the institution's TPS. Considerable TPS errors were found in 17% (n=45) of the head and neck irradiations. Also, 68% (n=13) of the irradiations that failed to meet the IROC-Houston criteria were found to have calculation errors.

Conclusions: Nearly 1 in 5 institutions were found to have TPS errors in their intensity modulated radiation therapy calculations, highlighting the need for careful beam modeling and calculation in the TPS. An independent recalculation system can help identify the presence of TPS errors and pass on the knowledge to the institution.
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http://dx.doi.org/10.1016/j.ijrobp.2017.03.049DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5567850PMC
August 2017

Development of a flattening filter free multiple source model for use as an independent, Monte Carlo, dose calculation, quality assurance tool for clinical trials.

Med Phys 2017 Sep 1;44(9):4952-4960. Epub 2017 Aug 1.

Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, TX, 77030, USA.

Purpose: The Imaging and Radiation Oncology Core-Houston (IROC-H) Quality Assurance Center (formerly the Radiological Physics Center) has reported varying levels of compliance from their anthropomorphic phantom auditing program. IROC-H studies have suggested that one source of disagreement between institution submitted calculated doses and measurement is the accuracy of the institution's treatment planning system dose calculations and heterogeneity corrections used. In order to audit this step of the radiation therapy treatment process, an independent dose calculation tool is needed.

Methods: Monte Carlo multiple source models for Varian flattening filter free (FFF) 6 MV and FFF 10 MV therapeutic x-ray beams were commissioned based on central axis depth dose data from a 10 × 10 cm field size and dose profiles for a 40 × 40 cm field size. The models were validated against open-field measurements in a water tank for field sizes ranging from 3 × 3 cm to 40 × 40 cm . The models were then benchmarked against IROC-H's anthropomorphic head and neck phantom and lung phantom measurements.

Results: Validation results, assessed with a ±2%/2 mm gamma criterion, showed average agreement of 99.9% and 99.0% for central axis depth dose data for FFF 6 MV and FFF 10 MV models, respectively. Dose profile agreement using the same evaluation technique averaged 97.8% and 97.9% for the respective models. Phantom benchmarking comparisons were evaluated with a ±3%/2 mm gamma criterion, and agreement averaged 90.1% and 90.8% for the respective models.

Conclusions: Multiple source models for Varian FFF 6 MV and FFF 10 MV beams have been developed, validated, and benchmarked for inclusion in an independent dose calculation quality assurance tool for use in clinical trial audits.
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http://dx.doi.org/10.1002/mp.12433DOI Listing
September 2017

Development of a Monte Carlo multiple source model for inclusion in a dose calculation auditing tool.

Med Phys 2017 Sep 1;44(9):4943-4951. Epub 2017 Aug 1.

Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, TX, 77030, USA.

Purpose: The Imaging and Radiation Oncology Core Houston (IROC-H) (formerly the Radiological Physics Center) has reported varying levels of agreement in their anthropomorphic phantom audits. There is reason to believe one source of error in this observed disagreement is the accuracy of the dose calculation algorithms and heterogeneity corrections used. To audit this component of the radiotherapy treatment process, an independent dose calculation tool is needed.

Methods: Monte Carlo multiple source models for Elekta 6 MV and 10 MV therapeutic x-ray beams were commissioned based on measurement of central axis depth dose data for a 10 × 10 cm field size and dose profiles for a 40 × 40 cm field size. The models were validated against open field measurements consisting of depth dose data and dose profiles for field sizes ranging from 3 × 3 cm to 30 × 30 cm . The models were then benchmarked against measurements in IROC-H's anthropomorphic head and neck and lung phantoms.

Results: Validation results showed 97.9% and 96.8% of depth dose data passed a ±2% Van Dyk criterion for 6 MV and 10 MV models respectively. Dose profile comparisons showed an average agreement using a ±2%/2 mm criterion of 98.0% and 99.0% for 6 MV and 10 MV models respectively. Phantom plan comparisons were evaluated using ±3%/2 mm gamma criterion, and averaged passing rates between Monte Carlo and measurements were 87.4% and 89.9% for 6 MV and 10 MV models respectively.

Conclusions: Accurate multiple source models for Elekta 6 MV and 10 MV x-ray beams have been developed for inclusion in an independent dose calculation tool for use in clinical trial audits.
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http://dx.doi.org/10.1002/mp.12426DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5603209PMC
September 2017

Reproducibility of patient setup in the seated treatment position: A novel treatment chair design.

J Appl Clin Med Phys 2017 Jan;18(1):223-229

Department of Radiation Physics, Division of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, USA.

Radiotherapy in a seated position may be indicated for patients who are unable to lie on the treatment couch for the duration of treatment, in scenarios where a seated treatment position provides superior anatomical positioning and dose distributions, or for a low-cost system designed using a fixed treatment beam and rotating seated patient. In this study, we report a novel treatment chair that was constructed to allow for three-dimensional imaging and treatment delivery while ensuring robust immobilization, providing reproducibility equivalent to that in the traditional supine position. Five patients undergoing radiation treatment for head-and-neck cancers were enrolled and were setup in the chair, with immobilization devices created, and then imaged with orthogonal X-rays in a scenario that mimicked radiation treatments (without treatment delivery). Six subregions of the acquired images were rigidly registered to evaluate intra- and interfraction displacement and chair construction. Displacements under conditions of simulated image guidance were acquired by first registering one subregion; the residual displacement of other subregions was then measured. Additionally, we administered a patient questionnaire to gain patient feedback and assess comparison to the supine position. Average inter- and intrafraction displacements of all subregions in the seated position were less than 2 and 3 mm, respectively. When image guidance was simulated, L-R and A-P interfraction displacements were reduced by an average of 1 mm, providing setup of comparable quality to supine setups. The enrolled patients, who had no indication for a seated treatment position, reported no preference in the seated or the supine position. The novel chair design provides acceptable inter- and intrafraction displacement, with reproducibility equivalent to that reported for patients in the supine position. Patient feedback will be incorporated in the refinement of the chair, facilitating treatment of head-and-neck cancer in patients who are unable to lie for the duration of treatment or for use in an economical fixed-beam setup.
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http://dx.doi.org/10.1002/acm2.12024DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5689874PMC
January 2017
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