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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

Presentations

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

Room: AAPM ePoster Library

Purpose:
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.
Methods:
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.
Results:
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%.
Conclusion:
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.

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

Keywords

Validation, Rotational Therapy, Semiconductor Detectors

Taxonomy

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

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