Clinical Implementation of a Model-Based In Vivo Dose Verification System for Stereotactic Body Radiation Therapy-Volumetric Modulated Arc Therapy Treatments Using the Electronic Portal Imaging Device.
To report findings from an in vivo dosimetry program implemented for all stereotactic body radiation therapy patients over a 31-month period and discuss the value and challenges of utilizing in vivo electronic portal imaging device (EPID) dosimetry clinically.



From December 2013 to July 2016, 117 stereotactic body radiation therapy-volumetric modulated arc therapy patients (100 lung, 15 spine, and 2 liver) underwent 602 EPID-based in vivo dose verification events. A developed model-based dose reconstruction algorithm calculates the 3-dimensional dose distribution to the patient by back-projecting the primary fluence measured by the EPID during treatment. The EPID frame-averaging was optimized in June 2015. For each treatment, a 3%/3-mm γ comparison between our EPID-derived dose and the Eclipse AcurosXB-predicted dose to the planning target volume (PTV) and the ≥20% isodose volume were performed. Alert levels were defined as γ pass rates <85% (lung and liver) and <80% (spine). Investigations were carried out for all fractions exceeding the alert level and were classified as follows: EPID-related, algorithmic, patient setup, anatomic change, or unknown/unidentified errors.



The percentages of fractions exceeding the alert levels were 22.6% for lung before frame-average optimization and 8.0% for lung, 20.0% for spine, and 10.0% for liver after frame-average optimization. Overall, mean (± standard deviation) planning target volume γ pass rates were 90.7% ± 9.2%, 87.0% ± 9.3%, and 91.2% ± 3.4% for the lung, spine, and liver patients, respectively.



Results from the clinical implementation of our model-based in vivo dose verification method using on-treatment EPID images is reported. The method is demonstrated to be valuable for routine clinical use for verifying delivered dose as well as for detecting errors.
Medical Physics Department, CancerCare Manitoba, Winnipeg, Manitoba, Canada. Electronic address: pmccowan@cancercare.mb.ca.
Peter M
PM
McCowan
Medical Physics Department, CancerCare Manitoba, Winnipeg, Manitoba, Canada.
Ganiyu
G
Asuni
Medical Physics Department, CancerCare Manitoba, Winnipeg, Manitoba, Canada; Department of Physics and Astronomy, University of Manitoba, Winnipeg, Manitoba, Canada.
Eric
E
Van Uytven
Medical Physics Department, CancerCare Manitoba, Winnipeg, Manitoba, Canada.
Timothy
T
VanBeek
Medical Physics Department, CancerCare Manitoba, Winnipeg, Manitoba, Canada; Department of Physics and Astronomy, University of Manitoba, Winnipeg, Manitoba, Canada; Department of Radiology, University of Manitoba, Winnipeg, Manitoba, Canada.
Boyd M C
BM
McCurdy
Department of Oncology, University of Calgary, Calgary, Alberta, Canada.
Shaun K
SK
Loewen
CancerCare Manitoba, Winnipeg, Manitoba, Canada.
Naseer
N
Ahmed
CancerCare Manitoba, Winnipeg, Manitoba, Canada.
Bashir
B
Bashir
CancerCare Manitoba, Winnipeg, Manitoba, Canada.
James B
JB
Butler
CancerCare Manitoba, Winnipeg, Manitoba, Canada.
Amitava
A
Chowdhury
CancerCare Manitoba, Winnipeg, Manitoba, Canada.
Arbind
A
Dubey
CancerCare Manitoba, Winnipeg, Manitoba, Canada.
Ahmet
A
Leylek
CancerCare Manitoba, Winnipeg, Manitoba, Canada.
Maged
M
Nashed
D000328:Adult; D000368:Aged; D003198:Computer Simulation; D004867:Equipment Design; D019544:Equipment Failure Analysis; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D009369:Neoplasms / Q000175:diagnosis / Q000503:physiopathology / Q000532:radiotherapy*; D011874:Radiometry / Q000295:instrumentation*; D016634:Radiosurgery / Q000295:instrumentation*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000295:instrumentation* / Q000379:methods; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014963:X-Ray Intensifying Screens