Publications by authors named "Slav Yartsev"

68 Publications

A Phase II Multi-institutional Clinical Trial Assessing Fractionated Simultaneous In-Field Boost Radiotherapy for Brain Oligometastases.

Cureus 2019 Dec 16;11(12):e6394. Epub 2019 Dec 16.

Radiation Oncology, London Regional Cancer Program, London Health Sciences Centre, London, CAN.

Purpose/Objective Published preclinical and phase I clinical trial data suggest that fractionated lesional radiotherapy with 60 Gy in 10 fractions can serve as an alternative approach to single fraction radiosurgical boost for brain oligometastases.  Methods and Materials A phase II clinical trial (NCT01543542) of a total of 60 Gy in 10 fractions of lesional (one to three) radiotherapy (given simultaneously with whole-brain helical tomotherapy with 30 Gy in 10 fractions) was conducted at five institutions. We hypothesized that fractionated radiotherapy would be considered unsuitable if the median overall survival (OS) was degraded by two months or if six-month intracranial control (ICC) and intracranial lesion (ILC) were inferior by 10% compared with the published RTOG 9508 results. Results A total of 87 patients were enrolled over a 4.5-year accrual period. Radiological lesion and extralesional central nervous system progression were documented in 15/87 (17%) and 11/87 (13%) patients, respectively. Median OS for all patients was 5.4 months. Six-month actuarial estimates of ICC and ILC were 78% and 89%, respectively. However, only the ILC estimate achieved statistical significance (p=0.02), demonstrating non-inferiority to the a priori historical controls (OS: p=0.09, ICC=0.31). Two patients developed suspected asymptomatic radionecrosis. Conclusions The phase II estimates of ILC were demonstrated to be non-inferior to the results of the RTOG 9508.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.7759/cureus.6394DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6959838PMC
December 2019

Proliferation saturation index in an adaptive Bayesian approach to predict patient-specific radiotherapy responses.

Int J Radiat Biol 2019 10 19;95(10):1421-1426. Epub 2019 Mar 19.

Department of Integrated Mathematical Oncology, H. Lee Moffitt Cancer Center & Research Institute , Tampa , FL , USA.

Radiotherapy prescription dose and dose fractionation protocols vary little between individual patients having the same tumor grade and stage. To personalize radiotherapy a predictive model is needed to simulate radiation response. Previous modeling attempts with multiple variables and parameters have been shown to yield excellent data fits at the cost of non-identifiability and clinically unrealistic results. We develop a mathematical model based on a proliferation saturation index (PSI) that is a measurement of pre-treatment tumor volume-to-carrying capacity ratio that modulates intrinsic tumor growth and radiation response rates. In an adaptive Bayesian approach, we utilize an increasing number of data points for individual patients to predict patient-specific responses to subsequent radiation doses. Model analysis shows that using PSI as the only patient-specific parameter, model simulations can fit longitudinal clinical data with high accuracy (=0.84). By analyzing tumor response to radiation using daily CT scans early in the treatment, response to the remaining treatment fractions can be predicted after two weeks with high accuracy (c-index = 0.89). The PSI model may be suited to forecast treatment response for individual patients and offers actionable decision points for mid-treatment protocol adaptation. The presented work provides an actionable image-derived biomarker prior to and during therapy to personalize and adapt radiotherapy.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1080/09553002.2019.1589013DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7081883PMC
October 2019

Prognostic Significance of Tumor Location for Liver Cancer Radiotherapy.

Cureus 2018 Dec 11;10(12):e3714. Epub 2018 Dec 11.

Medical Physics, London Regional Cancer Program, London, CAN.

Introduction According to the Surveillance, Epidemiology and End Results (SEER) data, cancerous involvement of the liver is on an increase over the last three decades. It occurs worldwide in all races and carries a poor prognosis. Currently, considerable progress has been made in patient selection, staging, surgery, chemotherapy agents, and stereotactic radiotherapy in both primary and metastatic liver cancers with improved outcomes. While there is evidence of the prognostic factors of liver function, the involvement of the portal vein, inferior vena cava thrombosis, lesion size, radiation dose, number of fractions, and SBRT techniques, there is no study evaluating outcomes with the location of the lesion. Our aim in this retrospective study was to explore the correlation of tumor location from the portal vein bifurcation (vascular wall) and the radiotherapy outcome (survival) in hepatocellular cancer. Methods Contrast-enhanced computed tomography (CT) studies in 86 patients with liver cancer were retrospectively reviewed in an institutional review board (IRB)-approved database to determine the distance to the bifurcation point of the portal vein from tumor's centre of mass (distance tumor bifurcation: DTB) and from the edge point of the planning target volume closest to the bifurcation (distance edge bifurcation: DEB). The mean dose to the sphere of 1 cm diameter around the bifurcation point (mean dose at bifurcation: MDB) was calculated. These parameters were tested as predictors of patient outcomes using univariate and multivariate analysis as two groups of patients. Results Only the DEB correlation with survival for hepatocellular carcinoma (HCC) was found to be significant (P = 0.028). A larger MDB is caused by a smaller DTB and a smaller DEB. The hazard ratio for DTB, DEB, and MDB were 0.48, 0.41, and 1.05, respectively. The DEB was found to be a better predictor of outcomes (overall survival) compared to the DTB and MDB parameters. The close proximity of the tumor to the blood supply vessels was a decisive factor. The DTB parameter is also dependent on the size of the tumor and this factor weakens the correlation of this parameter on survival data. The inclusion of the dosimetric and geometric location, as well as distance parameters in predictive models for liver cancer patients, was shown to benefit the pre-selection of treatment options for liver cancer patients treated with radiotherapy. Conclusion For hepatocellular cancer patients, the distance between the edge point of the planning treatment volume (PTV) to the portal vein bifurcation (DEB) of more than 2 cm was found to be a predictor of survival.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.7759/cureus.3714DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6373884PMC
December 2018

Online daily assessment of dose change in head and neck radiotherapy without dose-recalculation.

J Appl Clin Med Phys 2018 Sep 7;19(5):659-665. Epub 2018 Aug 7.

Department of Medical Biophysics, Western University, London, ON, Canada.

Background: Head and neck cancers are commonly treated with radiation therapy, but due to possible volume changes, plan adaptation may be required during the course of treatment. Currently, plan adaptations consume significant clinical resources. Existing methods to evaluate the need for plan adaptation requires deformable image registration (DIR) to a new CT simulation or daily cone beam CT (CBCT) images and the recalculation of the dose distribution. In this study, we explore a tool to assist the decision for plan adaptation using a CBCT without re-computation of dose, allowing for rapid online assessment.

Methods: This study involved 18 head and neck cancer patients treated with CBCT image guidance who had their treatment plan modified based on a new CT simulation (ReCT). Dose changes were estimated using different methods and compared to the current gold standard of using DIR between the planning CT scan (PCT) and ReCT with recomputed dose. The first and second methods used DIR between the PCT and daily CBCT with the planned dose or recalculated dose from the ReCT respectively, with the dose transferred to the CBCT using rigid registration. The necessity of plan adaptation was assessed by the change in dose to 95% of the planning target volume (D95) and mean dose to the parotids.

Results: The treatment plans were adapted clinically for all 18 patients but only 7 actually needed an adaptation yielding 11 unnecessary adaptations. Applying a method using the daily CBCT with the planned dose distribution would have yielded only four unnecessary adaptations and no missed adaptations: a significant improvement from that done clinically.

Conclusion: Using the DIR between the planning CT and daily CBCT can flag cases for plan adaptation before every fraction while not requiring a new re-planning CT scan and dose recalculation.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/acm2.12432DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6123138PMC
September 2018

Potential benefits of large database analysis.

Authors:
Slav Yartsev

Ann Transl Med 2017 Oct;5(20):413

London Regional Cancer Program, London Health Sciences Centre, London, ON, Canada.

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.21037/atm.2017.08.02DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5673787PMC
October 2017

Performance Characteristics of an Independent Dose Verification Program for Helical Tomotherapy.

J Med Phys 2017 Jul-Sep;42(3):156-162

London Regional Cancer Program, London Health Sciences Centre, London, ON, Canada.

Helical tomotherapy with its advanced method of intensity-modulated radiation therapy delivery has been used clinically for over 20 years. The standard delivery quality assurance procedure to measure the accuracy of delivered radiation dose from each treatment plan to a phantom is time-consuming. RadCalc, a radiotherapy dose verification software, has released specifically for beta testing a module for tomotherapy plan dose calculations. RadCalc's accuracy for tomotherapy dose calculations was evaluated through examination of point doses in ten lung and ten prostate clinical plans. Doses calculated by the TomoHDA™ tomotherapy treatment planning system were used as the baseline. For lung cases, RadCalc overestimated point doses in the lung by an average of 13%. Doses within the spinal cord and esophagus were overestimated by 10%. Prostate plans showed better agreement, with overestimations of 6% in the prostate, bladder, and rectum. The systematic overestimation likely resulted from limitations of the pencil beam dose calculation algorithm implemented by RadCalc. Limitations were more severe in areas of greater inhomogeneity and less prominent in regions of homogeneity with densities closer to 1 g/cm. Recommendations for RadCalc dose calculation algorithms and anatomical representation were provided based on the results of the study.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.4103/jmp.JMP_48_17DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5618463PMC
October 2017

Secondary Cutaneous Involvement in Follicular Diffuse Lymphoma Treated with Helical Tomotherapy.

Cureus 2017 Jul 14;9(7):e1471. Epub 2017 Jul 14.

Physics, London Regional Cancer Program, Western University.

Non-Hodgkin's lymphoma is a complex heterogeneous group of disease entities that involves nodal and extranodal tissues. Cutaneous involvement can occur either as a primary or secondary in course of disease. Radiation therapy with either total body or localized treatments is often used for local control and symptom relief, depending on the target volume. We describe a 60-year-old male with a remote history of stage IA left neck follicular lymphoma treated with radiation 20 years ago and previous relapses aggressively treated by chemotherapy. Treatment to a large volume of back and posterior shoulders on a helical tomotherapy radiotherapy system is reported. The skin lesions responded completely with no toxicity. Palliative radiotherapy to a fairly large and complex volume of skin with modest dose avoiding underlying critical tissues on tomotherapy is feasible, well tolerated with an excellent durable response, without compromising future chemotherapy and stem cell transplant for systemic relapse.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.7759/cureus.1471DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5598867PMC
July 2017

Representing the dosimetric impact of deformable image registration errors.

Phys Med Biol 2017 Aug 11;62(17):N391-N403. Epub 2017 Aug 11.

Department of Medical Biophysics, University of Western Ontario, London, ON, Canada.

Deformable image registration (DIR) is emerging as a tool in radiation therapy for calculating the cumulative dose distribution across multiple fractions of treatment. Unfortunately, due to the variable nature of DIR algorithms and dependence of performance on image quality, registration errors can result in dose accumulation errors. In this study, landmarked images were used to characterize the DIR error throughout an image space and determine its impact on dosimetric analysis. Ten thoracic 4DCT images with 300 landmarks per image study matching the end-inspiration and end-expiration phases were obtained from 'dir-labs'. DIR was performed using commercial software MIM Maestro. The range of dose uncertainty (RDU) was calculated at each landmark pair as the maximum and minimum of the doses within a sphere around the landmark in the end-expiration phase. The radius of the sphere was defined by a measure of DIR error which included either the actual DIR error, mean DIR error per study, constant errors of 2 or 5 mm, inverse consistency error, transitivity error or the distance discordance metric (DDM). The RDUs were evaluated using the magnitude of dose uncertainty (MDU) and inclusion rate (IR) of actual error lying within the predicted RDU. The RDU was calculated for 300 landmark pairs on each 4DCT study for all measures of DIR error. The most representative RDU was determined using the actual DIR error with a MDU of 2.5 Gy and IR of 97%. Across all other measures of DIR error, the DDM was most predictive with a MDU of 2.5 Gy and IR of 86%, closest to the actual DIR error. The proposed method represents the range of dosimetric uncertainty of DIR error using either landmarks at specific voxels or measures of registration accuracy throughout the volume.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1088/1361-6560/aa8133DOI Listing
August 2017

Technical Note: Comparison of megavoltage, dual-energy, and single-energy CT-based μ-maps for a four-channel breast coil in PET/MRI.

Med Phys 2017 Sep 25;44(9):4758-4765. Epub 2017 Jul 25.

London Regional Cancer Program, Physics and Engineering Dept., London, ON, Canada.

Purpose: The purpose of this study was to describe and evaluate methods for calculating a megavoltage computed tomography (MVCT)-derived MR hardware attenuation map (μ-map) and dual-energy CT (DECT) for 511 keV photons.

Methods: Phantom measurements were acquired on a whole-body hybrid PET/MRI system, using a four-channel receive-only MR radiofrequency (RF) breast coil. Two acquisitions were performed: with the phantoms positioned in the four-channel RF breast coil, and without the breast coil. PET attenuation from the breast coil was corrected using three different CT-derived hardware μ-maps: (a) Single-energy CT (SECT), (b) DECT, and (c) MVCT. Each attenuation-corrected (AC) PET volume was evaluated and compared with the acquisition performed without the breast coil.

Results: The breast coil attenuated PET photons by 10% overall. Threshold values were applied to the SECT μ-map to reduce the effects of metal artifacts, but overcorrection occurred in more highly attenuated regions. The DECT-derived virtual monochromatic image reduced beam-hardening artifacts, but other metal artifacts remained. Despite the remaining metal artifacts in the DECT image, it led to an improvement in the more attenuated regions. The MVCT images appear to be free from metal artifacts leading to an artifact-free μ-map and a further improvement AC-PET images.

Conclusions: Our MVCT-based approach for creating μ-maps for MR RF coils greatly reduces artifacts produced by metal in a SECT approach. This eliminates the need for other artifact reduction methods, including the application of a threshold of narrow beam attenuation coefficients, or disassembling hardware to remove high-Z components before imaging with a kilovoltage source.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/mp.12407DOI Listing
September 2017

Optimization of brain metastases radiotherapy with TomoHDA.

Med Dosim 2017 Spring;42(1):53-56. Epub 2017 Jan 24.

London Regional Cancer Program, London Health Sciences Centre and Departments of Oncology and Medical Biophysics, Western University, London, ON, Canada.

An upgrade of the helical tomotherapy technology by introducing variable fan-field width (dynamic jaws) reduced the penumbra in superior-inferior direction for the target. Possible implementation of this upgrade even for the cases of the targets with different dose prescriptions is proposed. An example of brain metastasis in proximity to the optical apparatus in need of the whole brain irradiation of 30 Gy and higher dose to the lesion is considered.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.meddos.2016.11.003DOI Listing
September 2017

Potential benefit of rotational radiation therapy.

Future Oncol 2017 04 9;13(10):873-874. Epub 2017 Jan 9.

Department of Medical Biophysics, Western University, London, ON, Canada.

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.2217/fon-2016-0535DOI Listing
April 2017

Target margins in radiotherapy of prostate cancer.

Br J Radiol 2016 Nov 20;89(1067):20160312. Epub 2016 Jul 20.

1 London Regional Cancer Program, London Health Sciences Centre, London, ON, Canada.

We reviewed the literature on the use of margins in radiotherapy of patients with prostate cancer, focusing on different options for image guidance (IG) and technical issues. The search in PubMed database was limited to include studies that involved external beam radiotherapy of the intact prostate. Post-prostatectomy studies, brachytherapy and particle therapy were excluded. Each article was characterized according to the IG strategy used: positioning on external marks using room lasers, bone anatomy and soft tissue match, usage of fiducial markers, electromagnetic tracking and adapted delivery. A lack of uniformity in margin selection among institutions was evident from the review. In general, introduction of pre- and in-treatment IG was associated with smaller planning target volume (PTV) margins, but there was a lack of definitive experimental/clinical studies providing robust information on selection of exact PTV values. In addition, there is a lack of comparative research regarding the cost-benefit ratio of the different strategies: insertion of fiducial markers or electromagnetic transponders facilitates prostate gland localization but at a price of invasive procedure; frequent pre-treatment imaging increases patient in-room time, dose and labour; online plan adaptation should improve radiation delivery accuracy but requires fast and precise computation. Finally, optimal protocols for quality assurance procedures need to be established.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1259/bjr.20160312DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5124838PMC
November 2016

A multivariable model to predict survival for patients with hepatic carcinoma or liver metastasis receiving radiotherapy.

Future Oncol 2017 Jan 1;13(1):19-30. Epub 2016 Sep 1.

Department of Medical Biophysics, Western University, London, ON, Canada.

Aim: New parameters that correlate with overall survival were identified in patients with liver lesions treated with radiation therapy.

Methods: Pretreatment information and parameters of radiation treatment plans for 129 metastatic and 66 hepatocellular carcinoma liver cancer patients were analyzed. Study end points included overall survival collected from patient charts and electronic records.

Results: Two practical nomograms were constructed for primary hepatocellular carcinoma and liver metastasis patients. For patients with a Child-Pugh A, radiation dose escalation provided a significant survival benefit. However, for those with Child-Pugh B or C, increasing dose does not impact on survival.

Conclusion: The developed models can potentially guide dose selection and provide prognostic information but still require external validation.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.2217/fon-2016-0252DOI Listing
January 2017

Quantitative Perfusion and Permeability Biomarkers in Brain Cancer from Tomographic CT and MR Images.

Biomark Cancer 2016 3;8(Suppl 2):47-59. Epub 2016 Jul 3.

Department of Radiology, University of Calgary, Calgary, AB, Canada.; Department of Clinical Neurosciences, University of Calgary, Calgary, AB, Canada.; Hotchkiss Brain Institute, University of Calgary, Calgary, AB, Canada.; Seaman Family MR Centre, Foothills Medical Centre, Calgary, AB, Canada.

Dynamic contrast-enhanced perfusion and permeability imaging, using computed tomography and magnetic resonance systems, are important techniques for assessing the vascular supply and hemodynamics of healthy brain parenchyma and tumors. These techniques can measure blood flow, blood volume, and blood-brain barrier permeability surface area product and, thus, may provide information complementary to clinical and pathological assessments. These have been used as biomarkers to enhance the treatment planning process, to optimize treatment decision-making, and to enable monitoring of the treatment noninvasively. In this review, the principles of magnetic resonance and computed tomography dynamic contrast-enhanced perfusion and permeability imaging are described (with an emphasis on their commonalities), and the potential values of these techniques for differentiating high-grade gliomas from other brain lesions, distinguishing true progression from posttreatment effects, and predicting survival after radiotherapy, chemotherapy, and antiangiogenic treatments are presented.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.4137/BIC.S31801DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4933536PMC
July 2016

Assessment of function and quality of life in a phase II multi-institutional clinical trial of fractionated simultaneous in-field boost radiotherapy for patients with 1-3 metastases.

J Neurooncol 2016 07 15;128(3):431-6. Epub 2016 Apr 15.

Division of Radiation Oncology, London Health Sciences Centre, A4-901B, 790 Commissioners Rd. E, London, ON, N6A4L6, Canada.

We examined functional outcomes and quality of life of whole brain radiotherapy (WBRT) with integrated fractionated stereotactic radiotherapy boost (FSRT) for brain metastases treatment. Eighty seven people with 1-3 brain metastases (54/87 lung primary, 42/87 single brain metastases) were enrolled on this Phase II trial of WBRT (30 Gy/10) + simultaneous FSRT, (60 Gy/10). Median overall follow-up and survival was 5.4 months, 6 month actuarial intra-lesional control was 78 %; only 1 patient exhibited grade 4 toxicity (worsened seizures); most treatment related toxicity was grade 1 or 2; 2/87 patients demonstrated asymptomatic radiation necrosis on follow-up imaging. Mean (Min-Max) baseline KPS, Mini Mental Status Exam (MMSE) and FACT-BR quality of life were 83 (70-100), 28 (21-30) and 143 (98-153). Lower baseline MMSE (but not KPS or FACT-Br) was associated with worse survival after adjusting for age, number of metastases, primary and extra-cranial disease status. Crude rates of deterioration (>10 points decrease from baseline for KPS and FACT-Br, MMSE fall to <27) ranged from 26 to 38 % for KPS, 32-59 % for FACT-Br and 0-16 % for MMSE depending on the time-point assessed with higher rates generally noted at earlier time points (≤6 months post-treatment). Using a linear mixed models analysis, significant declines from baseline were noted for KPS and FACT-Br (largest effects at 6 weeks to 3 months) with no significant change in MMSE. The effects on function and quality of life of this integrated treatment of WBRT + simultaneous FSRT were similar to other published series combining WBRT + radiosurgery.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1007/s11060-016-2128-7DOI Listing
July 2016

Evaluation of CT Perfusion Biomarkers of Tumor Hypoxia.

PLoS One 2016 14;11(4):e0153569. Epub 2016 Apr 14.

Department of Medical Biophysics, Western University, London, Ontario, Canada.

Background: Tumor hypoxia is associated with treatment resistance to cancer therapies. Hypoxia can be investigated by immunohistopathologic methods but such procedure is invasive. A non-invasive method to interrogate tumor hypoxia is an attractive option as such method can provide information before, during, and after treatment for personalized therapies. Our study evaluated the correlations between computed tomography (CT) perfusion parameters and immunohistopathologic measurement of tumor hypoxia.

Methods: Wistar rats, 18 controls and 19 treated with stereotactic radiosurgery (SRS), implanted with the C6 glioma tumor were imaged using CT perfusion on average every five days to monitor tumor growth. A final CT perfusion scan and the brain were obtained on average 14 days (8-22 days) after tumor implantation. Tumor hypoxia was detected immunohistopathologically with pimonidazole. The tumor, necrotic, and pimonidazole-positive areas on histology samples were measured. Percent necrotic area and percent hypoxic areas were calculated. Tumor volume (TV), blood flow (BF), blood volume (BV), and permeability-surface area product (PS) were obtained from the CT perfusion studies. Correlations between CT perfusion parameters and histological parameters were assessed by Spearman's ρ correlation. A Bonferroni-corrected P value < 0.05 was considered significant.

Results: BF and BV showed significant correlations with percent hypoxic area ρ = -0.88, P < 0.001 and ρ = -0.81, P < 0.001, respectively, for control animals and ρ = -0.7, P < 0.001 and ρ = -0.6, P = 0.003, respectively, for all animals, while TV and BV were correlated (ρ = -0.64, P = 0.01 and ρ = -0.43, P = 0.043, respectively) with percent necrotic area. PS was not correlated with either percent necrotic or percent hypoxic areas.

Conclusions: Percent hypoxic area provided significant correlations with BF and BV, suggesting that CT perfusion parameters are potential non-invasive imaging biomarkers of tumor hypoxia.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0153569PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4831843PMC
September 2016

In regard to "Setup error analysis in helical tomotherapy based image-guided radiation therapy treatments".

Authors:
Slav Yartsev

J Med Phys 2016 Jan-Mar;41(1):71

London Regional Cancer Program, London Health Sciences Centre, London, Ontario, Canada.

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.4103/0971-6203.177275DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4795421PMC
April 2016

Patient-specific imaging schedules.

Authors:
Slav Yartsev

J Cancer Res Ther 2015 Oct-Dec;11(4):1042

Department of Oncology and Medical Biophysics, University of Western Ontario, London Regional Cancer Program, London Health Sciences Centre, London, Ontario, Canada.

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.4103/0973-1482.146139DOI Listing
June 2016

Erratum to: Survival prediction in high-grade gliomas using CT perfusion imaging.

J Neurooncol 2015 Oct;125(1):223-4

Neuroradiology Unit, Department of Neurosciences and Rehabilitation, Azienda Ospedaliero-Universitaria, Arcispedale S. Anna, Ferrara, Italy.

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1007/s11060-015-1946-3DOI Listing
October 2015

Separating the dosimetric consequences of changing tumor anatomy from positional uncertainty for conventional fractionated lung cancer patients.: In Regard to Grams et al.

Pract Radiat Oncol 2015 Sep-Oct;5(5):e553-e554

Department of Physics and Engineering, London Regional Cancer Program, London Health Sciences Centre, London, Ontario, Canada.

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.prro.2015.02.003DOI Listing
November 2015

Survival prediction in high-grade gliomas using CT perfusion imaging.

J Neurooncol 2015 May 11;123(1):93-102. Epub 2015 Apr 11.

Department of Medical Biophysics, Western University, London, ON, Canada.

Patients with high-grade gliomas usually have heterogeneous response to surgery and chemoirradiation. The objectives of this study were (1) to evaluate serial changes in tumor volume and perfusion imaging parameters and (2) to determine the value of these data in predicting overall survival (OS). Twenty-nine patients with World Health Organization grades III and IV gliomas underwent magnetic resonance (MR) and computed tomography (CT) perfusion examinations before surgery, and 1, 3, 6, 9, and 12 months after radiotherapy. Serial measurements of tumor volumes and perfusion parameters were evaluated by receiver operating characteristic analysis, Cox proportional hazards regression, and Kaplan-Meier survival analysis to determine their values in predicting OS. Higher trends in blood flow (BF), blood volume (BV), and permeability-surface area product in the contrast-enhancing lesions (CEL) and the non-enhancing lesions (NEL) were found in patients with OS < 18 months compared to those with OS ≥ 18 months, and these values were significant at selected time points (P < 0.05). Only CT perfusion parameters yielded sensitivities and specificities of ≥ 70% in predicting 18 and 24 months OS. Pre-surgery BF in the NEL and BV in the CEL and NEL 3 months after radiotherapy had sensitivities and specificities >80% in predicting 24 months OS in patients with grade IV gliomas. Our study indicated that CT perfusion parameters were predictive of survival and could be useful in assessing early response and in selecting adjuvant treatment to prolong survival if verified in a larger cohort of patients.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1007/s11060-015-1766-5DOI Listing
May 2015

Dynamic perfusion CT in brain tumors.

Eur J Radiol 2015 Dec 23;84(12):2386-92. Epub 2015 Feb 23.

Department of Medical Biophysics, The University of Western Ontario, 1151 Richmond Street N., London, Ontario, Canada N6A 5C1; Robarts Research Institute, The University of Western Ontario, 1151 Richmond St. N., London, Ontario, Canada N6A 5B7; Department of Oncology, The University of Western Ontario, Victoria Hospital, London Health Sciences Centre, 790 Commissioners Road East, London, Ontario, Canada N6A 4L6; Department of Medical Imaging, The University of Western Ontario, Victoria Hospital, London Health Sciences Centre, London, Ontario, Canada N6A 5W9; Lawson Imaging Program, Lawson Health Research Institute, 268 Grosvenor Street, London, Ontario, Canada N6A 4V2. Electronic address:

Dynamic perfusion CT (PCT) is an imaging technique for assessing the vascular supply and hemodynamics of brain tumors by measuring blood flow, blood volume, and permeability-surface area product. These PCT parameters provide information complementary to histopathologic assessments and have been used for grading brain tumors, distinguishing high-grade gliomas from other brain lesions, differentiating true progression from post-treatment effects, and predicting prognosis after treatments. In this review, the basic principles of PCT are described, and applications of PCT of brain tumors are discussed. The advantages and current challenges, along with possible solutions, of PCT are presented.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.ejrad.2015.02.012DOI Listing
December 2015

CT perfusion imaging as an early biomarker of differential response to stereotactic radiosurgery in C6 rat gliomas.

PLoS One 2014 17;9(10):e109781. Epub 2014 Oct 17.

Department of Medical Biophysics, Western University, London, Ontario, Canada; Department of Oncology, Western University, London, Ontario, Canada; London Regional Cancer Program, London, Ontario, Canada.

Background: The therapeutic efficacy of stereotactic radiosurgery for glioblastoma is not well understood, and there needs to be an effective biomarker to identify patients who might benefit from this treatment. This study investigated the efficacy of computed tomography (CT) perfusion imaging as an early imaging biomarker of response to stereotactic radiosurgery in a malignant rat glioma model.

Methods: Rats with orthotopic C6 glioma tumors received either mock irradiation (controls, N = 8) or stereotactic radiosurgery (N = 25, 12 Gy in one fraction) delivered by Helical Tomotherapy. Twelve irradiated animals were sacrificed four days after stereotactic radiosurgery to assess acute CT perfusion and histological changes, and 13 irradiated animals were used to study survival. Irradiated animals with survival >15 days were designated as responders while those with survival ≤15 days were non-responders. Longitudinal CT perfusion imaging was performed at baseline and regularly for eight weeks post-baseline.

Results: Early signs of radiation-induced injury were observed on histology. There was an overall survival benefit following stereotactic radiosurgery when compared to the controls (log-rank P<0.04). Responders to stereotactic radiosurgery showed lower relative blood volume (rBV), and permeability-surface area (PS) product on day 7 post-stereotactic radiosurgery when compared to controls and non-responders (P<0.05). rBV and PS on day 7 showed correlations with overall survival (P<0.05), and were predictive of survival with 92% accuracy.

Conclusions: Response to stereotactic radiosurgery was heterogeneous, and early selection of responders and non-responders was possible using CT perfusion imaging. Validation of CT perfusion indices for response assessment is necessary before clinical implementation.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0109781PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4201465PMC
July 2015

Comparative analysis of image guidance in two institutions for prostate cancer patients.

Rep Pract Oncol Radiother 2014 May 2;19(3):206-13. Epub 2014 Jan 2.

2nd Radiotherapy Department, Greater Poland Cancer Centre, Poznan, Poland.

Aim/background: The analysis of systematic and random errors obtained from the pooled data on inter-fraction prostate motion during radiation therapy in two institutions.

Materials And Methods: Data of 6085 observations for 216 prostate cancer patients treated on tomotherapy units in two institutions of position correction shifts obtained by co-registration of planning and daily CT studies were investigated. Three independent variables: patient position (supine or prone), target (prostate or prostate bed), and imaging mode (normal or coarse) were analyzed. Systematic and random errors were evaluated and used to calculate the margins for different options of referencing based on the position corrections observed with one, three, or five imaging sessions.

Results: Statistical analysis showed that only the difference between normal and coarse modes of imaging was significant, which allowed to merge the supine and prone position sub-groups as well as the prostate and prostate bed patients. In the normal and coarse imaging groups, the margins calculated using systematic and random errors in the medio-lateral and cranio-caudal directions (5.5 mm and 4.5 mm, respectively) were similar, but significantly different (5.3 mm for the normal mode and 7.1 mm for the coarse mode) in the anterio-posterior direction. The reference scheme based on the first three fractions (R3) was found to be the optimal one.

Conclusions: The R3 reference scheme effectively reduced systematic and random errors. Larger margins in the anterio-posterior direction should be used during prostate treatment on the tomotherapy unit, as coarse imaging mode is chosen in order to reduce imaging time and dose.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.rpor.2013.12.001DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4056535PMC
May 2014

Assessment of interpatient heterogeneity in tumor radiosensitivity for nonsmall cell lung cancer using tumor-volume variation data.

Med Phys 2014 Jun;41(6):064101

Department of Radiation Oncology, University of Washington, 1959 NE Pacific Street, Seattle, Washington 98195-6043.

Purpose: In our previous work, the authors showed that a distribution of cell surviving fractions S2 in a heterogeneous group of patients could be derived from tumor-volume variation curves during radiotherapy for head and neck cancer. In this research study, the authors show that this algorithm can be applied to other tumors, specifically in nonsmall cell lung cancer. This new application includes larger patient volumes and includes comparison of data sets obtained at independent institutions.

Methods: Our analysis was based on two data sets of tumor-volume variation curves for heterogeneous groups of 17 patients treated for nonsmall cell lung cancer with conventional dose fractionation. The data sets were obtained previously at two independent institutions by using megavoltage computed tomography. Statistical distributions of cell surviving fractions S2 and clearance half-lives of lethally damaged cells T(1/2) have been reconstructed in each patient group by using a version of the two-level cell population model of tumor response and a simulated annealing algorithm. The reconstructed statistical distributions of the cell surviving fractions have been compared to the distributions measured using predictive assays in vitro.

Results: Nonsmall cell lung cancer presents certain difficulties for modeling surviving fractions using tumor-volume variation curves because of relatively large fractional hypoxic volume, low gradient of tumor-volume response, and possible uncertainties due to breathing motion. Despite these difficulties, cell surviving fractions S2 for nonsmall cell lung cancer derived from tumor-volume variation measured at different institutions have similar probability density functions (PDFs) with mean values of 0.30 and 0.43 and standard deviations of 0.13 and 0.18, respectively. The PDFs for cell surviving fractions S2 reconstructed from tumor volume variation agree with the PDF measured in vitro.

Conclusions: The data obtained in this work, when taken together with the data obtained previously for head and neck cancer, suggests that the cell surviving fractions S2 can be reconstructed from the tumor volume variation curves measured during radiotherapy with conventional fractionation. The proposed method can be used for treatment evaluation and adaptation.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1118/1.4875686DOI Listing
June 2014

Improving quantitative CT perfusion parameter measurements using principal component analysis.

Acad Radiol 2014 May;21(5):624-32

Lawson Imaging, Lawson Health Research Institute, London, ON, Canada; Robarts Research Institute, Western University, 1151 Richmond St. N., London, Ontario, N6A 5B7, Canada; Department of Medical Biophysics, Western University, London, ON, Canada; Department of Medical Imaging, Western University, London, ON, Canada; Department of Oncology, Western University, London, ON, Canada. Electronic address:

Rationale And Objectives: To evaluate the improvements in measurements of blood flow (BF), blood volume (BV), and permeability-surface area product (PS) after principal component analysis (PCA) filtering of computed tomography (CT) perfusion images. To evaluate the improvement in CT perfusion image quality with poor contrast-to-noise ratio (CNR) in vivo.

Materials And Methods: A digital phantom with CT perfusion images reflecting known values of BF, BV, and PS was created and was filtered using PCA. Intraclass correlation coefficients and Bland-Altman analysis were used to assess reliability of measurements and reduction in measurement errors, respectively. Rats with C6 gliomas were imaged using CT perfusion, and the raw CT perfusion images were filtered using PCA. Differences in CNR, BF, BV, and PS before and after PCA filtering were assessed using repeated measures analysis of variance.

Results: From simulation, mean errors decreased from 12.8 (95% confidence interval [CI] = -19.5 to 45.0) to 1.4 mL/min/100 g (CI = -27.6 to 30.4), 0.2 (CI = -1.1 to 1.4) to -0.1 mL/100 g (CI = -1.1 to 0.8), and 2.9 (CI = -2.4 to 8.1) to 0.2 mL/min/100 g (CI = -3.5 to 3.9) for BF, BV, and PS, respectively. Map noise in BF, BV, and PS were decreased from 51.0 (CI = -3.5 to 105.5) to 11.6 mL/min/100 g (CI = -7.9 to 31.2), 2.0 (CI = 0.7 to 3.3) to 0.5 mL/100 g (CI = 0.1 to 1.0), and 8.3 (CI = -0.8 to 17.5) to 1.4 mL/min/100 g (CI = -0.4 to 3.1), respectively. For experiments, CNR significantly improved with PCA filtering in normal brain (P < .05) and tumor (P < .05). Tumor and brain BFs were significantly different from each other after PCA filtering with four principal components (P < .05).

Conclusions: PCA improved image CNR in vivo and reduced the measurement errors of BF, BV, and PS from simulation. A minimum of four principal components is recommended.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.acra.2014.01.015DOI Listing
May 2014

Optimization of tomotherapy treatment planning for patients with bilateral hip prostheses.

Radiat Oncol 2014 Feb 4;9:43. Epub 2014 Feb 4.

London Regional Cancer Program, London Health Sciences Centre, 790 Commissioners Road East, London, ON N6A 4L6, Canada.

Background: To determine the effect of different imaging options and the most efficient imaging strategy for treatment planning of patients with hip prostheses.

Methods: The planning kilovoltage CT (kVCT) and daily megavoltage CT (MVCT) studies for three prostate cancer patients with bilateral hip prostheses were used for creating hybrid kVCT/MVCT image sets. Treatment plans were created for kVCT images alone, hybrid kVCT/MVCT images, and MVCT images alone using the same dose prescription and planning parameters. The resulting dose volume histograms were compared. The orthopedic metal artifact reduction (O-MAR) reconstruction tool for kVCT images and different MVCT options were investigated with a water tank fit with double hip prostheses. Treatment plans were created for all imaging options and calculated dose was compared with the one measured by a pin-point ion chamber.

Results: On average for three patients, the D35% for the bladder was 8% higher in plans based on MVCT images and 7% higher in plans based on hybrid images, compared to the plans based on kVCT images alone. Likewise, the D35% for the rectum was 3% higher than the kVCT based plan for both hybrid and MVCT plans. The average difference in planned D99% in the PTV compared to kVCT plans was 0.9% and 0.1% for MVCT and hybrid plans, respectively. For the water tank with hip prostheses phantom, the kVCT plan with O-MAR correction applied showed better agreement between the measured and calculated dose than the original image set, with a difference of -1.9% compared to 3.3%. The measured doses for the MVCT plans were lower than the calculated dose due to image size limitations. The best agreement was for the kVCT/MVCT hybrid plans with the difference between calculated and measured dose around 1%.

Conclusion: MVCT image provides better visualization of patient anatomy and hybrid kVCT/MVCT study enables more accurate calculations using updated MVCT relative electron density calibration.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1186/1748-717X-9-43DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3922545PMC
February 2014

Relationship of computed tomography perfusion and positron emission tomography to tumour progression in malignant glioma.

J Med Radiat Sci 2014 Feb 16;61(1):4-13. Epub 2014 Jan 16.

London Regional Cancer Program, London Health Sciences Centre Ontario, Canada, N6A 4L6 ; Department of Medical Biophysics, The University of Western Ontario Ontario, Canada, N6A 5C1 ; Department of Oncology, The University of Western Ontario, London Health Sciences Centre, London Regional Cancer Program Ontario, Canada, N6A 4L6.

IntroductionThis study aimed to explore the potential for computed tomography (CT) perfusion and 18-Fluorodeoxyglucose positron emission tomography (FDG-PET) in predicting sites of future progressive tumour on a voxel-by-voxel basis after radiotherapy and chemotherapy. MethodsTen patients underwent pre-radiotherapy magnetic resonance (MR), FDG-PET and CT perfusion near the end of radiotherapy and repeated post-radiotherapy follow-up MR scans. The relationships between these images and tumour progression were assessed using logistic regression. Cross-validation with receiver operating characteristic (ROC) analysis was used to assess the value of these images in predicting sites of tumour progression. ResultsPre-radiotherapy MR-defined gross tumour; near-end-of-radiotherapy CT-defined enhancing lesion; CT perfusion blood flow (BF), blood volume (BV) and permeability-surface area (PS) product; FDG-PET standard uptake value (SUV); and SUV:BF showed significant associations with tumour progression on follow-up MR imaging (P < 0.0001). The mean sensitivity (±standard deviation), specificity and area under the ROC curve (AUC) of PS were 0.64 ± 0.15, 0.74 ± 0.07 and 0.72 ± 0.12 respectively. This mean AUC was higher than that of the pre-radiotherapy MR-defined gross tumour and near-end-of-radiotherapy CT-defined enhancing lesion (both AUCs = 0.6 ± 0.1, P ≤ 0.03). The multivariate model using BF, BV, PS and SUV had a mean AUC of 0.8 ± 0.1, but this was not significantly higher than the PS only model. ConclusionPS is the single best predictor of tumour progression when compared to other parameters, but voxel-based prediction based on logistic regression had modest sensitivity and specificity.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/jmrs.37DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4175825PMC
February 2014

Helical tomotherapy quality assurance with ArcCHECK.

Med Dosim 2014 13;39(2):159-62. Epub 2014 Jan 13.

London Regional Cancer Program, London Health Sciences Centre, London, Ontario, Canada. Electronic address:

To design a quality assurance (QA) procedure for helical tomotherapy that measures multiple beam parameters with 1 delivery and uses a rotating gantry to simulate treatment conditions. The customized QA procedure was preprogrammed on the tomotherapy operator station. The dosimetry measurements were performed using an ArcCHECK diode array and an A1SL ion chamber inserted in the central holder. The ArcCHECK was positioned 10cm above the isocenter so that the 21-cm diameter detector array could measure the 40-cm wide tomotherapy beam. During the implementation of the new QA procedure, separate comparative measurements were made using ion chambers in both liquid and solid water, the tomotherapy onboard detector array, and a MapCHECK diode array for a period of 10 weeks. There was good agreement (within 1.3%) for the beam output and cone ratio obtained with the new procedure and the routine QA measurements. The measured beam energy was comparable (0.3%) to solid water measurement during the 10-week evaluation period, excluding 2 of the 10 measurements with unusually high background. The symmetry reading was similarly compromised for those 2 weeks, and on the other weeks, it deviated from the solid water reading by ~2.5%. The ArcCHECK phantom presents a suitable alternative for performing helical tomotherapy QA, provided the background is collected properly. The proposed weekly procedure using ArcCHECK and water phantom makes the QA process more efficient.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.meddos.2013.12.002DOI Listing
January 2015

Treatment planning studies in radiotherapy.

Radiother Oncol 2013 Dec;109(3):342-3

London Regional Cancer Program, London Health Sciences Centre, Canada. Electronic address:

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.radonc.2013.11.008DOI Listing
December 2013
-->