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Dose Verification of Constant Dose Rate and Constant Gantry Speed Arc Therapy (CDRCAS-IMAT) Planning Using 2D Detector Array

R Zhang1, W Bai2*, Y Feng1, W Jiang1, H Meng1, (1)Department of Biomedical Engineering, Tianjin University, Tianjin, China (2)The Fourth Hospital of Hebei Medical University, Shijiazhuang, Hebei


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

2D detector arrays have become the standard device for verification of intensity modulated dose distributions. While when it is used in a stationary phantom for arc therapy, the measured dose is dependent on the beam angle. Aim of this work is to investigate the clinical usage of dose verification of CDRCAS-IMAT plans by using 2D-array ion chambers, and to develop an efficient way to validate the dose delivered for the patients during treatments.
A pixel-segmented ionisation chamber device, IMRT MatriXX™ from IBA with solid water phantom (withabuild-up of 5 cm and backscatter of 5cm) were used. Firstly, we developed correction factors (CFs) for each detector element (1020 CFs) in the Monaco TPS with a 5? interval for dose calculation and the dose was delivered according to the treatment plan developed with TPS. And the accuracy of these CFs were investigated by verifying 12 CDR-CAS-IMAT brain plans. The results were evaluated by the absolute and relative doses as well as Gamma (?) function.
The dose distributions measured by the MatriXX 2D array after applying beam angular-dependent CFs were in good agreements with plans calculated by planning system. In the comparison of the pixel-segmented ionisation chamber versus treatment planning system using the 3 mm/3% ?-function criteria, the mean passing rates of 3 mm dose grid with ?-parameter =1 were 96.87% and 97.83%, in two orthogonal planes, respectively. The Deviation between the measured dose and predicted dose in the selected points was within ±2.5%, except for the gantry position at 90? and 180? the discrepancy were noted for one of the ion chambers up to 12% and 8%.
The combination of MatriXX with solid water phantom with beam angular-dependent CFs proved to be a reliable method for pretreatment verification of CDRCAS-IMAT with sufficient accuracy.

Funding Support, Disclosures, and Conflict of Interest: This work partly supported by the Natural Science Foundation of Hebei Province of China (Grant No. H2018206135).


Validation, Rotational Therapy, Semiconductor Detectors


TH- External Beam- Photons: Quality Assurance - IMRT/VMAT

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