Publications by authors named "Parham Alaei"

29 Publications

  • Page 1 of 1

Generation of material-specific energy deposition kernels for kilovoltage x-ray dose calculations.

Med Phys 2021 Jun 26. Epub 2021 Jun 26.

Department of Radiation Oncology, University of Minnesota, Minneapolis, MN, USA.

Purpose: Dose calculation of kilovoltage x rays used in Image-Guided Radiotherapy has been investigated in recent years using various methods. Among these methods are model-based ones that suffer from inaccuracies in high-density materials and at interfaces when used in the kilovoltage energy range. The main reason for this is the use of water energy deposition kernels and simplifications employed such as density scaling in heterogeneous media. The purpose of this study was to produce and characterize material-specific energy deposition kernels, which could be used for dose calculations in this energy range. These kernels will also have utility in dose calculations in superficial radiation therapy and orthovoltage beams utilized in small animal irradiators.

Methods: Water energy deposition kernels with various resolutions; and high-resolution, material-specific energy deposition kernels were generated in the energy range of 10-150 kVp, using the EGSnrc Monte Carlo toolkit. The generated energy deposition kernels were further characterized by calculating the effective depth of penetration, the effective radial distance, and the effective lateral distance. A simple benchmarking of the kernels against Monte Caro calculations has also been performed.

Results: There was good agreement with previously reported water kernels, as well as between kernels with different resolution. The evaluation of effective depth of penetration, and radial and laterals distances, defines the relationship between energy, material density, and the shape of the material-specific kernels. The shape of these kernels becomes more forwardly scattered as the energy and material density are increased. The comparison of the dose calculated using the kernels with Monte Carlo provides acceptable results.

Conclusions: Water and material-specific energy deposition kernels in the kilovoltage energy range have been generated, characterized, and compared to previous work. These kernels will have utility in dose calculations in this energy range once algorithms capable of employing them are fully developed.
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http://dx.doi.org/10.1002/mp.15061DOI Listing
June 2021

First Multimodal, Three-Dimensional, Image-Guided Total Marrow Irradiation Model for Preclinical Bone Marrow Transplantation Studies.

Int J Radiat Oncol Biol Phys 2021 Jun 11. Epub 2021 Jun 11.

Department of Radiation Oncology, City of Hope Medical Center, Duarte, California; Beckman Research Institute of City of Hope, Duarte, California; Department of Radiation Oncology, University of Minnesota, Minneapolis, Minnesota. Electronic address:

Purpose: Total marrow irradiation (TMI) has significantly advanced radiation conditioning for hematopoietic cell transplantation in hematologic malignancies by reducing conditioning-induced toxicities and improving survival outcomes in relapsed/refractory patients. However, the relapse rate remains high, and the lack of a preclinical TMI model has hindered scientific advancements. To accelerate TMI translation to the clinic, we developed a TMI delivery system in preclinical models.

Methods And Materials: A Precision X-RAD SmART irradiator was used for TMI model development. Images acquired with whole-body contrast-enhanced computed tomography (CT) were used to reconstruct and delineate targets and vital organs for each mouse. Multiple beam and CT-guided Monte Carlo-based plans were performed to optimize doses to the targets and to vary doses to the vital organs. Long-term engraftment and reconstitution potential were evaluated by a congenic bone marrow transplantation (BMT) model and serial secondary BMT, respectively. Donor cell engraftment was measured using noninvasive bioluminescence imaging and flow cytometry.

Results: Multimodal imaging enabled identification of targets (skeleton and spleen) and vital organs (eg, lungs, gut, liver). In contrast to total body irradiation (TBI), TMI treatment allowed variation of radiation dose exposure to organs relative to the target dose. Dose reduction mirrored that in clinical TMI studies. Similar to TBI, mice treated with different TMI regimens showed full long-term donor engraftment in primary BMT and second serial BMT. The TBI-treated mice showed acute gut damage, which was minimized in mice treated with TMI.

Conclusions: A novel multimodal image guided preclinical TMI model is reported here. TMI conditioning maintained long-term engraftment with reconstitution potential and reduced organ damage. Therefore, this TMI model provides a unique opportunity to study the therapeutic benefit of reduced organ damage and BM dose escalation to optimize treatment regimens in BMT and hematologic malignancies.
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http://dx.doi.org/10.1016/j.ijrobp.2021.06.001DOI Listing
June 2021

First clinical implementation of GammaTile permanent brain implants after FDA clearance.

Brachytherapy 2021 May-Jun;20(3):673-685. Epub 2021 Jan 22.

Department of Radiation Oncology, University of Minnesota, Minneapolis, MN.

Purpose: GammaTile cesium-131 (Cs) permanent brain implant has received Food and Drug Administration (FDA) clearance as a promising treatment for certain brain tumors. Our center was the first institution in the United States after FDA clearance to offer the clinical use of GammaTile brachytherapy outside of a clinical trial. The purpose of this work is to aid the medical physicist and radiation oncologist in implementing this collagen carrier tile brachytherapy (CTBT) program in their practice.

Methods: A total of 23 patients have been treated with GammaTile to date at our center. Treatment planning system (TPS) commissioning was performed by configuring the parameters for the Cs (IsoRay Model CS-1, Rev2) source, and doses were validated with the consensus data from the American Association of Physicists in Medicine TG-43U1S2. Implant procedures, dosimetry, postimplant planning, and target delineations were established based on our clinical experience. Radiation safety aspects were evaluated based on exposure rate measurements of implanted patients, as well as body and ring badge measurements.

Results: An estimated timeframe of the GammaTile clinical responsibilities for the medical physicist, radiation oncologist, and neurosurgeon is presented. TPS doses were validated with published dose to water for Cs. Clinical aspects, including estimation of the number of tiles, treatment planning, dosimetry, and radiation safety considerations, are presented.

Conclusion: The implementation of the GammaTile program requires collaboration from multiple specialties, including medical physics, radiation oncology, and neurosurgery. This manuscript provides a roadmap for the implementation of this therapy.
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http://dx.doi.org/10.1016/j.brachy.2020.12.005DOI Listing
January 2021

How low can you go? A CBCT dose reduction study.

J Appl Clin Med Phys 2021 Feb 15;22(2):85-89. Epub 2021 Jan 15.

Department of Radiation Oncology, University of Minnesota, Minneapolis, MN, USA.

Purpose: Cone beam computed tomography (CBCT) is often used for patient setup based solely on bony anatomy. The goal of this work was to evaluate whether CBCT dose can be lowered to the level of kV image pair doses when used for bony anatomy-based IGRT without compromising positioning accuracy.

Methods: An anthropomorphic phantom was CT scanned in the head, head and neck, chest, and pelvis regions and setup on the linear accelerator couch with the isocenter near the planned location. Cone beam computed tomographies were performed with the standard "full dose" protocol supplied by the linac vendor. With sequentially lowering the dose, three-dimensional (3D) matching was performed for each without shifting the couch. The standard kV image pair protocol for each site was also used to image the phantoms. For all studies, six degrees of freedom was included in the 2D or 3D matching to the extent they could be employed. Imaging doses were determined in air at isocenter following the TG-61 formalism.

Results: Cone beam computed tomography dose was reduced by 81-98% of the standard CBCT protocol to nearly that of the standard kV image pair dose for each site. Relative to the standard CBCT shift values, translational shifts were within 0.3 and 1.6 mm for all sites, for the reduced dose CBCT and kV image pair, respectively. Rotational shifts were within 0.2 degree and 0.7 degrees for all sites, for the reduced dose CBCTs and kV image pair, respectively.

Conclusion: For bony anatomy-based image guidance, CBCT dose can be reduced to a value similar to that of a kV image pair with similar or better patient positioning accuracy than kV image pair alignment. Where rotations are important to correct, CBCT will be superior to orthogonal kV imaging without significantly increased imaging dose. This is especially important for image guidance for pediatric patient treatments.
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http://dx.doi.org/10.1002/acm2.13164DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7882101PMC
February 2021

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

Two-dimensional dose reconstruction using scatter correction of portal images.

J Cancer Res Ther 2019 Jul-Sep;15(5):1011-1017

Department of Medical Physics, Royal Adelaide Hospital, Adelaide, SA, Australia.

Context: Electronic portal imaging devices (EPIDs) could potentially be useful for patient setup verification and are also increasingly used for dosimetric verification. The accuracy of EPID for dose verification is dependent on the dose-response characteristics, and without a comprehensive evaluation of dose-response characteristics, EPIDs should not be used clinically.

Aims: A scatter correction method is presented which is based on experimental data of a two-dimensional (2D) ion chamber array. An accurate algorithm for 2D dose reconstruction at midplane using portal images for in vivo dose verification has been developed.

Subjects And Methods: The procedure of scatter correction and dose reconstruction was based on the application of several corrections for beam attenuation, and off-axis factors, measured using a 2D ion chamber array. 2D dose was reconstructed in slab phantom, OCTAVIUS 4D system, and patient, by back projection of transit dose map at EPID-sensitive layer using percentage depth dose data and inverse square. Verification of the developed algorithm was performed by comparing dose values reconstructed in OCTAVIUS 4D system and with that provided by a treatment planning system.

Results: The gamma analysis for dose planes within the OCTAVIUS 4D system showed 98% ±1% passing rate, using a 3%/3 mm pass criteria. Applying the algorithm for dose reconstruction in patient pelvic plans showed gamma passing rate of 96% ±2% using the same pass criteria.

Conclusions: An accurate empirical algorithm for 2D patient dose reconstruction has been developed. The algorithm was applied to phantom and patient data sets and is able to calculate dose in the midplane. Results indicate that the EPID dose reconstruction algorithm presented in this work is suitable for clinical implementation.
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http://dx.doi.org/10.4103/jcrt.JCRT_376_17DOI Listing
July 2020

Effect of beam configuration with inaccurate or incomplete small field output factors on the accuracy of treatment planning dose calculation.

Med Phys 2019 Nov 28;46(11):5273-5283. Epub 2019 Sep 28.

Department of Radiation Oncology, University of Minnesota, Minneapolis, MN, 55455, USA.

Purpose: To evaluate the effect of beam configuration with inaccurate or incomplete small field output factors on the accuracy of dose calculations in treatment planning systems.

Methods: Output factors were measured using various detectors and for a range of field sizes. Three types of treatment machines were configured in two treatment planning systems. In the first (corrected) machine, the Exradin W1 scintillator was used to determine output factors. In the second (uncorrected) machine, the measured output factors by the A1SL ion chamber without considering output correction factors for small field sizes were utilized. In the third (clinical) machine, measured output factors by the Exradin W1 were used but not for field sizes smaller than 2 × 2 cm . The dose computed by the anisotropic analytical algorithm (AAA), Acuros XB (AXB) and collapsed cone convolution/superposition (CCC) algorithms in the three machines were delivered using static (jaw-, MLC-, and jaw/MLC-defined), and composite [intensity modulated radiation therapy (IMRT), volumetric modulated arc therapy (VMAT)] fields. The differences between measured and calculated dose values were analyzed.

Results: For static fields, the percentage differences between measured and calculated doses by the three algorithms in three configured machines were <2% for field sizes larger than 2 × 2 cm . In jaw- and jaw/MLC-defined fields smaller than 2 × 2 cm , the corrected machine presented better agreement with measurement. Considering output correction factors in MLC-defined fields, among the three configured machines, the accuracy of calculation improved to within ±0.5%. For MLC-defined field size of 1 × 1 cm , AXB showed the smallest percentage difference (1%). In IMRT and VMAT plans, the percentage differences between measured and calculated doses at the isocenter, as well as the gamma analysis of different plans, which include field sizes larger than 3 × 3 cm , did not vary noticeably. For smaller field sizes, using the corrected machine influences dose calculation accuracy.

Conclusion: Configuration with corrected output factors improves accuracy of dose calculation for static field sizes smaller than 2 × 2 cm . For very small fields, the robustness of the dose calculation algorithm affects the accuracy of dose as well. In IMRT and VMAT plans, which include small subfields, the size of the jaw-defined field is an important factor and using corrected output factors increases dose calculation accuracy.
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http://dx.doi.org/10.1002/mp.13796DOI Listing
November 2019

Multi-institutional evaluation of MVCT guided patient registration and dosimetric precision in total marrow irradiation: A global health initiative by the international consortium of total marrow irradiation.

Radiother Oncol 2019 12 14;141:275-282. Epub 2019 Aug 14.

Department of Radiation Oncology, Beckman Research Institute, City of Hope, Duarte, USA. Electronic address:

Purpose: Total marrow irradiation (TMI) is a highly conformal treatment of the human skeleton structure requiring a high degree of precision and accuracy for treatment delivery. Although many centers worldwide initiated clinical studies using TMI, currently there is no standard for pretreatment patient setup. To this end, the accuracy of different patient setups was measured using pretreatment imaging. Their impact on dose delivery was assessed for multiple institutions.

Methods And Materials: Whole body imaging (WBI) or partial body imaging (PBI) was performed using pretreatment megavoltage computed tomography (MVCT) in a helical Tomotherapy machine. Rigid registration of MVCT and planning kilovoltage computed tomography images were performed to measure setup error and its effect on dose distribution. The entire skeleton was considered the planning target volume (PTV) with five sub regions: head/neck (HN), spine, shoulder and clavicle (SC), and one avoidance structure, the lungs. Sixty-eight total patients (>300 images) across six institutions were analyzed.

Results: Patient setup techniques differed between centers, creating variations in dose delivery. Registration accuracy varied by anatomical region and by imaging technique, with the lowest to the highest degree of pretreatment rigid shifts in the following order: spine, pelvis, HN, SC, and lungs. Mean fractional dose was affected in regions of high registration mismatch, in particular the lungs.

Conclusions: MVCT imaging and whole body patient immobilization was essential for assessing treatment setup, allowing for the complete analysis of 3D dose distribution in the PTV and lungs (or avoidance structures).
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http://dx.doi.org/10.1016/j.radonc.2019.07.010DOI Listing
December 2019

Technical Note: Impact of region of interest size and location in Gafchromic film dosimetry.

Med Phys 2018 May 18;45(5):2329-2336. Epub 2018 Apr 18.

Department of Radiation Oncology, University of Minnesota, Minneapolis, MN, 55455, USA.

Purpose: To evaluate dependence of measured dose on size and location of region of interest (ROI) in Gafchromic EBT3 film dosimetry.

Methods: Gafchromic EBT3 films were irradiated perpendicularly using the 6MV beam from a linear accelerator at 10 cm depth (100 cm SSD) of a 30 × 30 × 20 cm solid water phantom for a range of field sizes of 6 × 6 to 100 × 100 mm . ImageJ software was used for reading pieces of film. The appropriate location of ROIs in scanned films was found by two methods. First, the ROI was visually placed at the center of image. Second, the profile of pixel value versus distance was plotted and the center of profile was used for drawing ROI. Each scanned film was read using both methods and for three ROI sizes (1, 2, and 4 mm). A plastic scintillator, Exradin W1, was used as the reference dosimeter.

Results: Comparing the three ROI sizes using both methods showed that there was less than 2% difference from reference in output factor measurements for field sizes larger or equal to 10 × 10 mm . The percentage differences were increased in field sizes smaller than 10 × 10 mm and for ROI size of 4 × 4 mm for both centered-ROI and profiled-ROI methods. The mean percentage differences from reference measurements, for field sizes of 100 × 100 to 20 × 20 mm , were smaller than 1% in both methods of ROI positioning. For field sizes of 15 × 15 and 10 × 10 mm , the smaller mean percentage differences were observed in profiled-ROI (4 × 4 mm ) and centered-ROI (4 × 4 mm ). For the field sizes of 8 × 8 and 6 × 6 mm , the profiled-ROI (2 × 2 mm ) had smallest mean percentage difference, which was 0.88%.

Conclusion: The ROI size of 4 × 4 mm is appropriate for dose measurements in field sizes of 100 × 100 mm to 10 × 10 mm , regardless of the method of finding location of ROI. In field sizes smaller than 10 × 10 mm , finding location of the ROI by profile of pixel values increases the accuracy of measurement, and ROI size of 2 × 2 mm has the smallest difference from the reference dose measurements.
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http://dx.doi.org/10.1002/mp.12885DOI Listing
May 2018

Image guidance doses delivered during radiotherapy: Quantification, management, and reduction: Report of the AAPM Therapy Physics Committee Task Group 180.

Med Phys 2018 May 24;45(5):e84-e99. Epub 2018 Mar 24.

University of Pennsylvania, Philadelphia, PA, 19104, USA.

Background: With radiotherapy having entered the era of image guidance, or image-guided radiation therapy (IGRT), imaging procedures are routinely performed for patient positioning and target localization. The imaging dose delivered may result in excessive dose to sensitive organs and potentially increase the chance of secondary cancers and, therefore, needs to be managed.

Aims: This task group was charged with: a) providing an overview on imaging dose, including megavoltage electronic portal imaging (MV EPI), kilovoltage digital radiography (kV DR), Tomotherapy MV-CT, megavoltage cone-beam CT (MV-CBCT) and kilovoltage cone-beam CT (kV-CBCT), and b) providing general guidelines for commissioning dose calculation methods and managing imaging dose to patients.

Materials & Methods: We briefly review the dose to radiotherapy (RT) patients resulting from different image guidance procedures and list typical organ doses resulting from MV and kV image acquisition procedures.

Results: We provide recommendations for managing the imaging dose, including different methods for its calculation, and techniques for reducing it. The recommended threshold beyond which imaging dose should be considered in the treatment planning process is 5% of the therapeutic target dose.

Discussion: Although the imaging dose resulting from current kV acquisition procedures is generally below this threshold, the ALARA principle should always be applied in practice. Medical physicists should make radiation oncologists aware of the imaging doses delivered to patients under their care.

Conclusion: Balancing ALARA with the requirement for effective target localization requires that imaging dose be managed based on the consideration of weighing risks and benefits to the patient.
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http://dx.doi.org/10.1002/mp.12824DOI Listing
May 2018

Early assessment of dosimetric and biological differences of total marrow irradiation versus total body irradiation in rodents.

Radiother Oncol 2017 09 1;124(3):468-474. Epub 2017 Aug 1.

Department of Pediatrics, Division of Blood and Marrow Transplantation, University of Minnesota, Minneapolis, USA.

Purpose: To develop a murine total marrow irradiation (TMI) model in comparison with the total body irradiation (TBI) model.

Materials And Methods: Myeloablative TMI and TBI were administered in mice using a custom jig, and the dosimetric differences between TBI and TMI were evaluated. The early effects of TBI/TMI on bone marrow (BM) and organs were evaluated using histology, FDG-PET, and cytokine production. TMI and TBI with and without cyclophosphamide (Cy) were evaluated for donor cell engraftment and tissue damage early after allogeneic hematopoietic cell transplantation (HCT). Stromal derived factor-1 (SDF-1) expression was evaluated.

Results: TMI resulted in similar dose exposure to bone and 50% reduction in dose to bystander organs. BM histology was similar between the groups. In the non-HCT model, TMI mice had significantly less acute intestinal and lung injury compared to TBI. In the HCT model, recipients of TMI had significantly less acute intestinal injury and spleen GVHD, but increased early donor cell engraftment and BM:organ SDF-1 ratio compared to TBI recipients.

Conclusions: The expected BM damage was similar in both models, but the damage to other normal tissues was reduced by TMI. However, BM engraftment was improved in the TMI group compared to TBI, which may be due to enhanced production of SDF-1 in BM relative to other organs after TMI.
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http://dx.doi.org/10.1016/j.radonc.2017.07.018DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5624834PMC
September 2017

Evaluation of dose calculation accuracy of treatment planning systems at hip prosthesis interfaces.

J Appl Clin Med Phys 2017 May 20;18(3):9-15. Epub 2017 Mar 20.

Department of Radiation Oncology, University of Minnesota, Minneapolis, MN, 55455, USA.

There are an increasing number of radiation therapy patients with hip prosthesis. The common method of minimizing treatment planning inaccuracies is to avoid radiation beams to transit through the prosthesis. However, the beams often exit through them, especially when the patient has a double-prosthesis. Modern treatment planning systems employ algorithms with improved dose calculation accuracies but even these algorithms may not predict the dose accurately at high atomic number interfaces. The current study evaluates the dose calculation accuracy of three common dose calculation algorithms employed in two commercial treatment planning systems. A hip prosthesis was molded inside a cylindrical phantom and the dose at several points within the phantom at the interface with prosthesis was measured using thermoluminescent dosimeters. The measured doses were then compared to the predicted ones by the planning systems. The results of the study indicate all three algorithms underestimate the dose at the prosthesis interface, albeit to varying degrees, and for both low- and high-energy x rays. The measured doses are higher than calculated ones by 5-22% for Pinnacle Collapsed Cone Convolution algorithm, 2-23% for Eclipse Acuros XB, and 6-25% for Eclipse Analytical Anisotropic Algorithm. There are generally better agreements for AXB algorithm and the worst results are for the AAA.
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http://dx.doi.org/10.1002/acm2.12060DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5689850PMC
May 2017

Implementation of full/half bowtie filter models in a commercial treatment planning system for kilovoltage cone-beam CT dose estimations.

J Appl Clin Med Phys 2016 03 8;17(2):153-164. Epub 2016 Mar 8.

Baylor Scott & White Health.

The purpose of this study was to implement full/half bowtie filter models in a com-mercial treatment planning system (TPS) to calculate kilovoltage (kV) cone-beam CT (CBCT) doses of Varian On-Board Imager (OBI) kV X-ray imaging system. The full/half bowtie filter models were created as compensators in Pinnacle TPS using MATLAB software. The physical profiles of both bowtie filters were imported and hard-coded in the MATLAB system. Pinnacle scripts were written to import bowtie filter models into Pinnacle treatment plans. Bowtie filter-free kV X-ray beam models were commissioned and the bowtie filter models were validated by analyzing the lateral and percent-depth-dose (PDD) profiles of anterior/posterior X-ray beams in water phantoms. A CT dose index (CTDI) phantom was employed to calculate CTDI and weighted CTDI values for pelvis and pelvis-spotlight CBCT protocols. A five-year-old pediatric anthropomorphic phantom was utilized to evaluate absorbed and effective doses (ED) for standard and low-dose head CBCT protocols. The CBCT dose calculation results were compared to ion chamber (IC) and Monte Carlo (MC) data for the CTDI phantom and MOSFET and MC results for the pediatric phantom, respectively. The differences of lateral and PDD profiles between TPS calculations and IC measurements were within 6%. The CTDI and weighted CTDI values of the TPS were respectively within 0.25 cGy and 0.08 cGy compared to IC measurements. The absorbed doses ranged from 0 to 7.22 cGy for the standard dose CBCT and 0 to 1.56 cGy for the low-dose CBCT. The ED values were found to be 36-38 mSv and 7-8 mSv for the standard and low-dose CBCT protocols, respectively. This study demonstrated that the established full/half bowtie filter beam models can produce reasonable dose calculation results. Further study is to be performed to evaluate the models in clinical situations.
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http://dx.doi.org/10.1120/jacmp.v17i2.5988DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5874958PMC
March 2016

Dose response characteristics of a novel CCD camera-based electronic portal imaging device comparison with OCTAVIUS detector.

J Cancer Res Ther 2015 Oct-Dec;11(4):765-9

Department of Radiation Medicine Engineering, Shahid Beheshti University, Tehran, Iran.

Aim: Dosimetric properties of a CCD camera-based Electronic Portal Imaging Device (EPID) for clinical dosimetric application have been evaluated. Characteristics obtained by EPID also compared with commercial 2D array of ion chambers.

Materials And Methods: Portal images acquired in dosimetry mode then exported raw fluence or uncorrected images were investigated. Integration time of image acquisition mode has adjusted on 1 s per frame.

Results: As saturation of camera of the EPID, dose response does not have linear behavior. The slight nonlinearity of the camera response can be corrected by a logarithmic expression. A fourth order polynomial regression model with coefficient of determination of 0.998 predicts a response to absolute dose values at less than 50 cGy. A field size dependent response of up to 7% (0.99-1.06) relative OCTAVIUS detector measurement was found. The EPID response can be fitted by a cubic regression for field size changes, yielded coefficient of determination of 0.999.

Conclusions: These results indicate that the EPID is well suited for accurate dosimetric purposes, the major limitation currently being due to integration time and dead-time in frame acquisition.
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http://dx.doi.org/10.4103/0973-1482.148695DOI Listing
November 2016

Imaging dose from cone beam computed tomography in radiation therapy.

Phys Med 2015 Nov 4;31(7):647-58. Epub 2015 Jul 4.

School of Engineering, Cardiff University, Cardiff, Wales, UK; Velindre Cancer Centre, Cardiff, Wales, UK.

Imaging dose in radiation therapy has traditionally been ignored due to its low magnitude and frequency in comparison to therapeutic dose used to treat patients. The advent of modern, volumetric, imaging modalities, often as an integral part of linear accelerators, has facilitated the implementation of image-guided radiation therapy (IGRT), which is often accomplished by daily imaging of patients. Daily imaging results in additional dose delivered to patient that warrants new attention be given to imaging dose. This review summarizes the imaging dose delivered to patients as the result of cone beam computed tomography (CBCT) imaging performed in radiation therapy using current methods and equipment. This review also summarizes methods to calculate the imaging dose, including the use of Monte Carlo (MC) and treatment planning systems (TPS). Peripheral dose from CBCT imaging, dose reduction methods, the use of effective dose in describing imaging dose, and the measurement of CT dose index (CTDI) in CBCT systems are also reviewed.
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http://dx.doi.org/10.1016/j.ejmp.2015.06.003DOI Listing
November 2015

Characterization of an orthovoltage biological irradiator used for radiobiological research.

J Radiat Res 2015 May 17;56(3):485-92. Epub 2015 Feb 17.

Department of Radiation Oncology, University of Minnesota, 420 Delaware Street, SE MMC 494, Minneapolis, MN 55455, USA

Orthovoltage irradiators are routinely used to irradiate specimens and small animals in biological research. There are several reports on the characteristics of these units for small field irradiations. However, there is limited knowledge about use of these units for large fields, which are essential for emerging large-field irregular shape irradiations, namely total marrow irradiation used as a conditioning regimen for hematological malignancies. This work describes characterization of a self-contained Orthovoltage biological irradiator for large fields using measurements and Monte Carlo simulations that could be used to compute the dose for in vivo or in vitro studies for large-field irradiation using this or a similar unit. Percentage depth dose, profiles, scatter factors, and half-value layers were measured and analyzed. A Monte Carlo model of the unit was created and used to generate depth dose and profiles, as well as scatter factors. An ion chamber array was also used for profile measurements of flatness and symmetry. The output was determined according to AAPM Task Group 61 guidelines. The depth dose measurements compare well with published data for similar beams. The Monte Carlo-generated depth dose and profiles match our measured doses to within 2%. Scatter factor measurements indicate gradual variation of these factors with field size. Dose rate measured by placing the ion chamber atop the unit's steel plate or solid water indicate enhanced readings of 5 to 28% compared with those measured in air. The stability of output over a 5-year period is within 2% of the 5-year average.
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http://dx.doi.org/10.1093/jrr/rru129DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4426923PMC
May 2015

Dosimetry of an in-line kilovoltage imaging system and implementation in treatment planning.

Int J Radiat Oncol Biol Phys 2014 Mar 20;88(4):913-9. Epub 2014 Jan 20.

Department of Radiation Oncology, Saarland University Medical Center, Homburg/Saar, Germany.

Purpose: To present the beam properties of the Siemens 70-kV and 121-kV linear accelerator-mounted imaging modalities and commissioning of the 121-kV beam in the Philips Pinnacle treatment planning system (TPS); measurements in an Alderson phantom were performed for verification of the model and to estimate the cone-beam CT (CBCT) imaging dose in the head and neck, thorax, and pelvis.

Methods And Materials: The beam profiles and depth-dose curve were measured in an acrylic phantom using thermoluminescent dosimeters and a soft x-ray ionization chamber. Measurements were imported into the TPS, modeled, and verified by phantom measurements.

Results: Modeling of the profiles and the depth-dose curve can be achieved with good quality. Comparison with the measurements in the Alderson phantom is generally good; only very close to bony structures is the dose underestimated by the TPS. For a 200° arc CBCT of the head and neck, a maximum dose of 7 mGy is measured; the thorax and pelvis 360° CBCTs give doses of 4-10 mGy and 7-15 mGy, respectively.

Conclusions: Dosimetric characteristics of the Siemens kVision imaging modalities are presented and modeled in the Pinnacle TPS. Thermoluminescent dosimeter measurements in the Alderson phantom agree well with the calculated TPS dose, validating the model and providing an estimate of the imaging dose for different protocols.
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http://dx.doi.org/10.1016/j.ijrobp.2013.12.007DOI Listing
March 2014

Dose calculation and treatment plan optimization including imaging dose from kilovoltage cone beam computed tomography.

Acta Oncol 2014 Jun 17;53(6):839-44. Epub 2014 Jan 17.

Department of Radiation Oncology, University of Minnesota , Minneapolis, Minnesota , USA.

Background: With the increasing use of cone beam computed tomography (CBCT) for patient position verification and radiotherapy treatment adaptation, there is an increasing need to develop techniques that can take into account concomitant dose using a personalized approach.

Material And Methods: A total of 20 patients (10 pelvis and 10 head and neck) who had undergone radiation therapy using intensity modulated radiation therapy (IMRT) were selected and the dose from kV CBCT was retrospectively calculated using a treatment planning system previously commissioned for this purpose. The imaging dose was added to the CT images used for treatment planning and the difference in its addition prior to and after the planning was assessed.

Results: The additional isocenter dose as a result of daily CBCT is in the order of 3-4 cGy for 35-fraction head and neck and 23-47 cGy for 25-fraction pelvis cases using the standard head and neck and pelvis image acquisition protocols. The pelvic dose is especially dependent on patient size and body mass index (BMI), being higher for patients with lower BMI. Due to the low energy of the kV CBCT beam, the maximum energy deposition is at or near the surface with the highest dose being on the patient's left side for the head and neck (∼7 cGy) and on the posterior for the pelvic cases (∼80 cGy). Addition of imaging dose prior to plan optimization resulted in an average reduction of 4% in the plan monitor units and 5% in the number of control points.

Conclusion: Dose from daily kV CBCT has been added to patient treatment plans using previously commissioned kV CBCT beams in a treatment planning system. Addition of imaging dose can be included in IMRT treatment plan optimization and would facilitate customization of imaging protocol based on patient anatomy and location of isocenter.
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http://dx.doi.org/10.3109/0284186X.2013.875626DOI Listing
June 2014

Commissioning kilovoltage cone-beam CT beams in a radiation therapy treatment planning system.

J Appl Clin Med Phys 2012 Nov 8;13(6):3971. Epub 2012 Nov 8.

Department of Radiation Oncology, University of Minnesota, Minneapolis, MN 55455, USA.

The feasibility of accounting of the dose from kilovoltage cone-beam CT in treatment planning has been discussed previously for a single cone-beam CT (CBCT) beam from one manufacturer. Modeling the beams and computing the dose from the full set of beams produced by a kilovoltage cone-beam CT system requires extensive beam data collection and verification, and is the purpose of this work. The beams generated by Elekta X-ray volume imaging (XVI) kilovoltage CBCT (kV CBCT) system for various cassettes and filters have been modeled in the Philips Pinnacle treatment planning system (TPS) and used to compute dose to stack and anthropomorphic phantoms. The results were then compared to measurements made using thermoluminescent dosimeters (TLDs) and Monte Carlo (MC) simulations. The agreement between modeled and measured depth-dose and cross profiles is within 2% at depths beyond 1 cm for depth-dose curves, and for regions within the beam (excluding penumbra) for cross profiles. The agreements between TPS-calculated doses, TLD measurements, and Monte Carlo simulations are generally within 5% in the stack phantom and 10% in the anthropomorphic phantom, with larger variations observed for some of the measurement/calculation points. Dose computation using modeled beams is reasonably accurate, except for regions that include bony anatomy. Inclusion of this dose in treatment plans can lead to more accurate dose prediction, especially when the doses to organs at risk are of importance.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5718524PMC
http://dx.doi.org/10.1120/jacmp.v13i6.3971DOI Listing
November 2012

The effect of small field output factor measurements on IMRT dosimetry.

Med Phys 2012 Aug;39(8):4691-4

Department of Therapeutic Radiology-Radiation Oncology, University of Minnesota, Minneapolis, Minnesota 55455, USA.

Purpose: To evaluate how changes in the measured small field output factors affect the doses in intensity-modulated treatment planning.

Methods: IMRT plans were created using Philips Pinnacle treatment planning system. The plans were optimized to treat a cylindrical target 2 cm in diameter and 2 cm in length. Output factors for 2 × 2 and 3 × 3 cm(2) field sizes were changed by ±5%, ±10%, and ±20% increments from the baseline measurements and entered into the planning system. The treatment units were recommissioned in the treatment planning system after each modification of the output factors and treatment plans were reoptimized. All plans were delivered to a solid water phantom and dose measurements were made using an ionization chamber. The percentage differences between measured and computed doses were calculated. An Elekta Synergy and a Varian 2300CD linear accelerator were separately evaluated.

Results: For the Elekta unit, decreasing the output factors resulted in higher measured than computed doses by 0.8% for -5%, 3.6% for -10%, and 8.7% for -20% steps. Increasing the output factors resulted in lower doses by 2.9% for +5%, 5.4% for +10%, and 8.3% for +20% steps. For the Varian unit no changes were observed for either increased or decreased output factors.

Conclusions: The measurement accuracy of small field output factors are of importance especially when the treatment plan consists of small segments as in IMRT. The method proposed here could be used to verify the accuracy of the measured small field output factors for certain linear accelerators as well as to test the beam model. The Pinnacle treatment planning system model uses output factors as a function of jaw setting. Consequently, plans using the Elekta unit, which conforms the jaws to the segments, are sensitive to small field measurement accuracy. On the other hand, for the Varian unit, jaws are fixed and segments are modeled as blocked fields hence, the impact of small field output factors on IMRT monitor unit calculation is not evaluable by this method.
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http://dx.doi.org/10.1118/1.4736527DOI Listing
August 2012

Effect of multileaf collimator-defined segment size on S(c).

Med Phys 2010 Jun;37(6):2731-7

Department of Therapeutic Radiology-Radiation Oncology, University of Minnesota, Minneapolis, Minnesota 55455, USA.

Purpose: Tertiary multileaf collimators (MLCs) in certain linear accelerators have been found to influence the factor S(c). This effect on S(c) is often ignored at the time of commissioning and beam data collection since the scatter/output factors are usually measured with the MLCs retracted. This may be a negligible effect for majority of conventional radiotherapy portals since the jaws are set to conform with MLCs as closely as possible. In the case of IMRT treatments, however, the jaw is often set at a fixed size, and the MLCs form the segments, or control points, of each beam, thus the difference between MLC and jaw settings may be significant.

Methods: The authors quantified the magnitude of this scatter difference for various field sizes defined by MLCs and jaws and characterized the variation in this scatter with MLC and jaw settings. They measured S(c) and S(c,p) factors for square fields (apertures) of different sizes for jaw settings from 10 x 10 to 36 x 36 cm2.

Results: The data indicate that the larger the difference between MLC-defined aperture and jaw settings, the more significant the difference between the output factors. The authors fitted curves to the MLC output factors for any given jaw size in order to parametrize this aperture effect as a function of jaw and MLC setting.

Conclusions: The quantification of the change in the output factor due to MLCs may be important for better modeling of dose in IMRT deliveries and other applications such as in vivo dosimetry.
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http://dx.doi.org/10.1118/1.3431997DOI Listing
June 2010

The accuracy of inhomogeneity corrections in intensity modulated radiation therapy planning in Philips Pinnacle system.

Med Dosim 2011 7;36(3):240-5. Epub 2010 Jun 7.

Department of Therapeutic Radiology-Radiation Oncology, University of Minnesota, Minneapolis, MN 55455, USA.

The degree of accuracy of inhomogeneity corrections in a treatment planning system is dependent on the algorithm used by the system. The choice of field size, however, could have an effect on the calculation accuracy as well. There have been several evaluation studies on the accuracy of inhomogeneity corrections used by different algorithms. Most of these studies, however, focus on evaluating the dose in phantom using simplified geometry and open/static fields. This work focuses on evaluating the degree of dose accuracy in calculations involving intensity-modulated radiation therapy (IMRT) fields incident on a phantom containing both lung- and bone-equivalent heterogeneities using 6 and 10 MV beams. IMRT treatment plans were generated using the Philips Pinnacle treatment planning system and delivered to a phantom containing 55 thermoluminescent dosimeter (TLD) locations within the lung and bone and near the lung and bone interfaces with solid water. The TLD readings were compared with the dose predicted by the planning system. We find satisfactory agreement between planned and delivered doses, with an overall absolute average difference between measurement and calculation of 1.2% for the 6 MV and 3.1% for the 10 MV beam with larger variations observed near the interfaces and in areas of high-dose gradient. The results presented here demonstrate that the convolution algorithm used in the Pinnacle treatment planning system produces accurate results in IMRT plans calculated and delivered to inhomogeneous media, even in regions that potentially lack electronic equilibrium.
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http://dx.doi.org/10.1016/j.meddos.2010.03.010DOI Listing
November 2011

Inclusion of the dose from kilovoltage cone beam CT in the radiation therapy treatment plans.

Med Phys 2010 Jan;37(1):244-8

University of Minnesota, Minneapolis, Minnesota 55455, USA.

Purpose: Cone beam CT is increasingly being used for daily patient positioning verification during radiation therapy treatments. The daily use of CBCT could lead to accumulated patient doses higher than the older technique of weekly portal imaging. There have been several studies focusing on measurement or calculation of the patient dose from CBCT recently.

Methods: This study investigates the feasibility of configuring a kV x-ray source in a commercial treatment planning system to calculate the dose to patient resulting from an IGRT procedure. The method proposed in this article can be used to calculate dose from CBCT imaging procedure and include that in the patient treatment plans.

Results: The kilovoltage beam generated by the CBCT imager has been modeled using the planning system. The modeled profiles agree with the measured ones to within 5%. The modeled beam was used to calculate dose to phantom in the pelvic region and the calculations were compared to TLD measurements. The agreement between calculated and measured doses ranges from 0% to 19% in soft tissue with larger variations observed near and within the bone.

Conclusions: The modeling of the beam produces reasonable results and the dose calculation comparisons indicate the potential for computing kilovoltage CBCT doses using a treatment planning system. Further improvements in the dose calculation algorithm are necessary, especially for dose calculations in and near the bone.
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http://dx.doi.org/10.1118/1.3271582DOI Listing
January 2010

In vivo diode dosimetry for IMRT treatments generated by Pinnacle treatment planning system.

Med Dosim 2009 28;34(1):26-9. Epub 2008 Mar 28.

Therapeutic Radiology, University of Minnesota, Minneapolis, MN 55455, USA.

Dose verification using diodes has been proposed and used for intensity modulated radiation therapy (IMRT) treatments. We have previously evaluated diode response for IMRT deliveries planned with the Eclipse/Helios treatment planning system. The Pinnacle treatment planning system generates plans that are delivered in a different fashion than Eclipse. Whereas the Eclipse-generated segments are delivered in organized progression from one side of each field to the other, Pinnacle-generated segments are delivered in a much more randomized fashion to different areas within the field. This makes diode measurements at a point more challenging because the diode may be exposed fully or partially to multiple small segments during one single field's treatment as opposed to being exposed to very few segments scanning across the diode during an Eclipse-generated delivery. We have evaluated in vivo dosimetry for Pinnacle-generated IMRT plans and characterized the response of the diode to various size segments on phantom. We present results of patient measurements on approximately 300 fields, which show that 76% of measurements agree to within 10% of the treatment-plan generated calculated doses. Of the other 24%, about 11% are within 15% of the calculated dose. Comparison of these with phantom measurements indicates that many of the discrepancies are due to diode positioning on patients and increased diode response at short source-to-surface distances (SSDs), with the remainder attributable to other factors such as segment size and partial irradiation of the diode.
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http://dx.doi.org/10.1016/j.meddos.2008.01.002DOI Listing
March 2009

The use of a commercial QA device for daily output check of a helical tomotherapy unit.

Med Phys 2006 Oct;33(10):3680-2

Department of Therapeutic Radiology-Radiation Oncology, University of Minnesota, Mayo Mail Code 494 420 Delaware Street S.E., Minneapolis, Minnesota 55455, USA.

Helical tomotherapy radiation therapy units, due to their particular design and differences from a traditional linear accelerator, require different procedures by which to perform routine quality assurance (QA). One of the principal QA tasks that should be performed daily on any radiation therapy equipment is the output constancy check. The daily output check on a Hi-Art TomoTherapy unit is commonly performed utilizing ionization chambers placed inside a solid water phantom. This provides a good check of output at one point, but does not give any information on either energy or symmetry of the beam, unless more than one point is measured. This also has the added disadvantage that it has to be done by the physics staff. To address these issues, and to simplify the process, such that it can be performed by radiation therapists, we investigated the use of a commercially available daily QA device to perform this task. The use of this device simplifies the task of daily output constancy checks and eliminates the need for continued physics involvement. This device can also be used to monitor the constancy of beam energy and cone profile and can potentially be used to detect gross errors in the couch movement or laser alignment.
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http://dx.doi.org/10.1118/1.2348762DOI Listing
October 2006

Novel cytosine deaminase fusion gene enhances the effect of radiation on breast cancer in bone by reducing tumor burden, osteolysis, and skeletal fracture.

Clin Cancer Res 2006 May;12(10):3168-76

Department of Orthopaedic Surgery, University of Minnesota, Minneapolis, Minnesota 55455, USA.

Background: Painful breast carcinoma metastases in bone are a common manifestation of malignant disease. Eradication of these tumors can be evasive, and as a result, skeletal morbidity increases with disease progression.

Experimental Design: The treatment potential of cytosine deaminase (CD) gene therapy combined with radiation treatment was evaluated in vitro and in vivo using a 4T1 murine breast carcinoma model. 4T1 carcinoma cells were transduced with a fusion gene encoding the extracellular and transmembrane domains of the human nerve growth factor receptor and the cytoplasmic portion of the yeast CD gene (NGFR-CD(y)).

Results And Conclusions: CD-expressing tumor cells (4TCD(y)) were highly sensitive to treatment by 5-fluorocytosine prodrug (P < 0.0001). 5-Fluorocytosine treatment of 4TCD(y), but not 4T1 cells, enhanced the effects of radiation in vitro (P < 0.0001). 5-Fluorocytosine prodrug treatment also increased the therapeutic potential of radiation in vivo. Mice with 4TCD(y) intrafemoral tumors showed increased effectiveness of radiation based on improved reductions in tumor size, reductions in tumorigenic osteolysis, and a decrease in skeletal fractures (P < 0.01).
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http://dx.doi.org/10.1158/1078-0432.CCR-05-2729DOI Listing
May 2006

Performance evaluation and quality assurance of Varian enhanced dynamic wedges.

J Appl Clin Med Phys 2006 15;7(1):14-20. Epub 2006 Feb 15.

Department of Therapeutic Radiology-Radiation Oncology, University of Minnesota, Minneapolis, Minnesota 55455, USA.

Dynamic wedges have been used in clinical practice for many years. Obvious superiority of dynamic over physical wedges is accompanied by the increased overhead involved in verifying the accuracy and reliability of their use. Contrary to very limited QA required to ensure proper functioning of the physical wedges, dynamic wedges, like any other dynamic treatment, require a robust QA program. This work expands upon previous suggestions and describes a comprehensive QA program for Varian enhanced dynamic wedges (EDWs) and presents the results of an 18-month evaluation of these wedges. The QA program includes daily, monthly, and yearly tests and individual treatment QA at the onset of use of the EDWs. The results of the 18-month evaluation show reproducibility in the wedge factors of better than 1% and in dose profiles of better than 2% on a monthly basis. Daily output measurements are generally within 2% of expected values.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5722478PMC
http://dx.doi.org/10.1120/jacmp.v7i1.2170DOI Listing
April 2006

Implementation of enhanced dynamic wedges in Pinnacle treatment planning system.

Med Dosim 2005 ;30(4):228-32

Department of Therapeutic Radiology-Radiation Oncology, University of Minnesota, Minneapolis, MN 55455, USA.

Enhanced dynamic wedges (EDW) provide many advantages over traditional hard wedges for linear accelerator treatments. Along with these advantages comes the responsibility of ensuring that this complex technology delivers the correct dose to patients. This involves determining the enhanced dynamic wedge factors for various field sizes and depths for use in the hand calculation of monitor units (MUs). The accurate representation of dynamic wedges in the treatment planning computer must also be ensured. This is required so that the final isodose distributions are correct and the MUs calculated by the treatment planning computer match those determined by hand calculation. We have commissioned and implemented the use of EDW in the Pinnacle radiation therapy planning system. The modeled dose profiles agree with the measured ones with a maximum difference of 2%. The MUs generated by Pinnacle are also within 2% of those calculated independently. The process of data collection and verification, beam modeling, and a discussion of a potential pitfall encountered in this process are presented in this paper.
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http://dx.doi.org/10.1016/j.meddos.2005.08.003DOI Listing
March 2006

Comparison of dynamic and step-and-shoot intensity-modulated radiation therapy planning and delivery.

Med Dosim 2004 ;29(1):1-6

University of Minnesota, Minneapolis, MN 55455, USA.

Intensity-modulated radiation therapy (IMRT) is commonly delivered using the dynamic or segmental mode of multileaf collimators (DMLC or SMLC). Both methods are designed to deliver intensity-modulated beams as determined by inverse planning software. In this study, we have used the Helios IMRT planning system to generate ideal treatment plans for 10 cases of 2 common treatment sites (prostate and head and neck) and have investigated the actual treatment fluence distributions generated for each of the MLC leaf motion choices. The 2 dose delivery techniques were dosimetrically compared to each other and to the treatment plans. For each technique, point doses were measured in a water phantom using ionization chambers. Also for each technique, 2-dimensional dose distributions at a selected depth in a plastic phantom were obtained, using extended range film. The total delivery time and the number of monitor units (MU) delivered by each method were also compared. Our results indicate that the 2 delivery methods produce comparable results dosimetrically. For the cases reviewed, the delivery time was an average of 15% longer for SMLC deliveries, while the number of MUs (beam-on time) required by SMLC was an average of 15% fewer, than that for the DMLC. In the interest of simplicity, lower beam-on time, and potentially fewer mechanically-related problems, we think that the SMLC delivery technique may be the better choice when Helios is used for planning and Varian linear accelerators are used for delivery.
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http://dx.doi.org/10.1016/j.meddos.2003.10.002DOI Listing
July 2004
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