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Development of Novel Real Time in Vivo EPID Treatment Verification for Brachytherapy

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G Fonseca

G Fonseca1*, M Podesta1 , B Reniers1,2 , F Verhaegen1,3, (1) Department of Radiation Oncology (MAASTRO), GROW School for Oncology and Developmental Biology, Maastricht University Medical Center, Maastricht 6201 BN, The Netherlands.(2) Research Group NuTeC, CMK, Hasselt University, Agoralaan Gebouw H, Diepenbeek B-3590, Belgium. (3) Medical Physics Unit, Department of Oncology, McGill University, Montreal, Quebec H3G 1A4, Canada.


MO-AB-BRA-3 (Monday, August 1, 2016) 7:30 AM - 9:30 AM Room: Ballroom A

Purpose: High Dose Rate (HDR) brachytherapy treatments are employed worldwide to treat a wide variety of cancers. However, in vivo dose verification remains a challenge with no commercial dosimetry system available to verify the treatment dose delivered to the patient. We propose a novel dosimetry system that couples an independent Monte Carlo (MC) simulation platform and an amorphous silicon Electronic Portal Imaging Device (EPID) to provide real time treatment verification.
Methods: MC calculations predict the EPID response to the photon fluence emitted by the HDR source by simulating the patient, the source dwell positions and times, and treatment complexities such as tissue compositions/densities and different applicators. Simulated results are then compared against EPID measurements acquired with ~0.14s time resolution which allows dose measurements for each dwell position. The EPID has been calibrated using an Ir-192 HDR source and experiments were performed using different phantoms, including tissue equivalent materials (PMMA, lung and bone). A source positioning accuracy of 0.2 mm, without including the afterloader uncertainty, was ensured using a robotic arm moving the source.
Results: An EPID can acquire 3D Cartesian source positions and its response varies significantly due to differences in the material composition/density of the irradiated object, allowing detection of changes in patient geometry. The panel time resolution allows dose rate and dwell time measurements. Moreover, predicted EPID images obtained from clinical treatment plans provide anatomical information that can be related to the patient anatomy, mostly bone and air cavities, localizing the source inside of the patient using its anatomy as reference.
Conclusion: Results obtained show the feasibility of the proposed dose verification system that is capable to verify all the brachytherapy treatment steps in real time providing data about treatment delivery quality and also applicator/structure motion during or between treatments.

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