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Real-Time EPID & Cherenkov Imaging for 3D Dosimetry in a Water Phantom

P Bruza

P Bruza1*, J Andreozzi1 , D Gladstone1,2,4 , L Jarvis2,4 , J Rottmann3 , B Pogue1,2 , (1) Thayer School of Engineering, Dartmouth College, Hanover, NH, (2) Geisel School of Medicine, Dartmouth College, Lebanon, New Hampshire, (3) Brigham and Woman's Hospital, Dana-Farber Cancer Institute and Harvard Medical School, Boston, MA, (4) Norris Cotton Cancer Center, Lebanon, NH


TU-FG-205-10 (Tuesday, August 1, 2017) 1:45 PM - 3:45 PM Room: 205

Purpose: To reconstruct a three-dimensional dose distribution in a water phantom in real-time and with millimeter resolution during Volumetric Modulated Arc Therapy (VMAT).

Methods: Cine-mode acquisition of Cherenkov and portal images were combined with a novel online reconstruction scheme, providing real-time 3D dosimetry of MV X-ray beams in a water tank. Images from the electronic portal imaging device (EPID) are primarily used for geometric 3D beam definition, while the Cherenkov images serve for correction of both the depth dose and x-ray scatter distribution. Both data-streams are acquired with sub-millimeter resolution at 10 Hz frame-rates. The volumetric dose distribution was reconstructed at discrete time points during delivery of a dynamic VMAT radiotherapy plan for TG-119 C-Shape geometry. To assess the spatial accuracy of our technique, the profile of a static 8x8 cm² beam was reconstructed and compared with the reference dosimetric dataset.

Results: The Gamma analysis between the cross-beam profile of an 8x8 cm² static beam and a reference dosimetric dataset using a 3%/3mm distance-to-agreement criteria indicated 100% pass rate (Gamma<1 for all data points). The 3% dose difference was measured globally, relative to the point of maximum dose. Gamma analysis with more stringent 1%/1mm criteria yielded pass rate of 85.5%. The Gamma analysis between the laterally-projected VMAT dose distribution and the integrated Cherenkov image reported 85.4% pass rate, with the largest mismatch in the low dose, high gradient area.

Conclusion: A methodology for dynamic 3D dose reconstruction from combined EPID and Cherenkov images was successfully demonstrated for the delivery of static and dynamic radiotherapy plans. Good agreement between a reconstructed static beam and a reference dosimetric dataset indicates the potential of our technique for application in reference dosimetry. We have illustrated the reconstruction of cumulative dose deposited to a water phantom by a VMAT plan for TG-119 C-Shape geometry.

Funding Support, Disclosures, and Conflict of Interest: This work was supported by National Institutes of Health grants R01 CA109558, R44 CA199681 and F31 CA192473. Authors acknowledge NCI Cancer Center Support Grant 5P30 CA023108-37. B. Pogue is founder and president of DoseOptics LLC developing Cherenkov imaging systems, however this work was not supported by DoseOptics in any way.

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