Sci—Thur AM: YIS - 06: An EPID-based 3D patient dose verification method for SBRT-VMAT delivery

Journal Article · Fri Aug 15 04:00:00 EDT 2014 · Medical Physics

DOI:https://doi.org/10.1118/1.4894939· OSTI ID:22409502

McCowan, P. ^[1]; Uytven, E van; Beek, T van ^[2]; McCurdy, B ^[1]

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1. Department of Physics and Astronomy, University of Manitoba, Winnipeg, Manitoba (Canada)
2. Medical Physics Department, CancerCare Manitoba, Winnipeg, Manitoba (Canada)

Purpose: Stereotactic body radiation therapy (SBRT) delivered via volumetric modulated arc therapy (VMAT) can strongly benefit from an in vivo patient dose verification due to the large doses per fraction. Electronic portal imaging devices (EPIDs) can be utilized as a patient dose dosimeter. In this work we present a physics-based model which utilizes on-treatment EPID images to reconstruct the dose delivered to an anthropomorphic phantom during SBRT-VMAT delivery. Methods: An SBRT linac beam was modeled using Monte Carlo methods and verified with measured data. Our dose reconstruction model back-projects EPID measured focal fluence upstream of the patient and adds a predicted extra-focal fluence component. This fluence is forward projected onto the patient's density matrix and convolved with dose kernels to calculate dose. The model was validated for two prostate, three lung, and two spine SBRT-VMAT treatments. Results were compared to the treatment planning system's calculation. Results: 2%/2 mm chi comparison calculations gave pass rates for the whole volume, infield, and high dose region respectively, and no lower than: 98%, 95%, 99% for the prostate plans, 99%, 92%, 85% for the lung plans, and 91%, 85%, 81% for the spine plans. A 3%/3mm calculation gave pass rates no lower than 99%, 94%, and 90% for all dose regions for the prostate, lung, and spine respectively. Conclusions: We have developed a physics-based model which calculates delivered dose to phantom (or patient) for SBRT-VMAT delivery using on treatment EPID images. The accuracy of the results has allowed us to test this model clinically.

• OSTI ID: 22409502
• Journal Information: Medical Physics, Journal Name: Medical Physics Journal Issue: 8 Vol. 41; ISSN 0094-2405; ISSN MPHYA6
• Country of Publication: United States
• Language: English

Related Subjects

60 APPLIED LIFE SCIENCES
LINEAR ACCELERATORS
LUNGS
MONTE CARLO METHOD
PATIENTS
PHANTOMS
PROSTATE
RADIATION DOSES
RADIOTHERAPY
VERIFICATION
VERTEBRAE