An in vivo dose verification method for SBRT-VMAT delivery using the EPID
P M McCowan1, E Van Uytven2, T Van Beek2
1Department of Physics and Astronomy, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada and Medical Physics Department, CancerCare Manitoba, 675 McDermot Avenue, Winnipeg, Manitoba R3E 0V9, Canada.
Medical Physics
|December 4, 2015
Summary
This study presents a validated physics-based model using electronic portal imaging devices (EPIDs) to accurately calculate patient radiation doses during SBRT-VMAT treatments, enhancing treatment safety and accuracy for complex radiotherapy.
Area of Science:
- Medical Physics
- Radiation Oncology
- Radiotherapy Dosimetry
Background:
- Volumetric Modulated Arc Therapy (VMAT) and Stereotactic Body Radiation Therapy (SBRT) have increased treatment complexity.
- SBRT involves higher doses over fewer fractions, making accurate dose verification critical.
- Electronic Portal Imaging Devices (EPIDs) are readily available on linear accelerators and suitable for dosimetry.
Purpose of the Study:
- To customize and validate a physics-based model for in vivo dose reconstruction during SBRT-VMAT.
- To utilize on-treatment EPID images for precise 3D dose calculation in SBRT-VMAT.
- To improve patient safety through accurate dose verification in advanced radiotherapy.
Main Methods:
- Developed a physics-based model using Monte Carlo simulations for SBRT beam modeling.
- Employed a forward model to predict patient surface fluence and a collapsed cone convolution algorithm for dose calculation.
- Validated the model using anthropomorphic phantoms and actual patient data for prostate, lung, and spine SBRT-VMAT treatments.
Main Results:
- The model achieved high accuracy, with pass rates exceeding 91% for prostate, 88% for lung, and 86% for spine plans using a 2%/2 mm gamma comparison.
- Patient data validation showed 86% for lung and 95% for spine plans.
- A 3%/3 mm gamma comparison yielded pass rates above 93% for all treatment sites.
Conclusions:
- A robust, physics-based model for SBRT-VMAT dose reconstruction using EPID images has been successfully validated.
- The model's accuracy supports its suitability for clinical implementation in radiotherapy.
- Future applications include integration into adaptive radiotherapy for offline and real-time adjustments.
