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Automatic Selection of An Absolute-Dose Verification Point for Volumetric-Modulated Arc Therapy Via Dose Uncertainty Potential Accumulation Model

A Saito1*, T Nakashima1, D Kawahara1, E Shiba2,1, T Matsuura3,1, K Fukata4, K Miki1, M Tsuneda5, T Nishio5, Y Nagata1, (1) Hiroshima University, Hiroshima, JP, (2) University of Occupational and Environmental Health, Fukuoka, JP, (3) Hiroshima High-precision Radiotherapy Cancer Center, Hiroshima, JP, (4) Keio University, Tokyo, JP, (5) Tokyo Women's Medical University, Tokyo, JP


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

Room: AAPM ePoster Library

Purpose: To develop a method to automatically pick a measurement point at which the high accuracy of the dose measurement through the correlation analysis involving the dose (D), dose gradient (G), and dose uncertainty potential (U) for the volumetric-modulated arc therapy (VMAT).
Methods: We analyzed 208 verification plans of VMAT. The VMAT plans were created in the Eclipse treatment planning system using the RapidArc algorithm. Verification plans were created on a 18x18x18-cm3 cubic phantom. A measurement point with high-D and low-G was selected for each plan in the clinical practice. Three-dimensional U distribution was generated using our in-house software based on our previous studies. The verification measurement was performed using the CC04 ionization chamber. The dose uncertainty potential distribution in the cubic phantom was generated by our in-house software. For each plan, we analyzed correlations among D, G, and U for 729 points (from –4 to 4 cm with 1-cm step (9 positions) in each direction). We also selected a low U measurement point within high D (Top 10% of the D values) and compared them with a clinical measurement point for each plan.
Results: Most cases showed low G values for high D data, which were expected and utilized in clinical practice. Higher U values were observed for high D data. The selected measurement point by our software showed lower U values than the clinical measurement points for 93.3% of the examined cases.
Conclusion: We developed an automatic scheme to pick a measurement point with a low U value at which high accuracy of the dose measurement was expected. This technique is expected to improve the selection of the measurement point for the absolute dose verification in clinical practice.

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Intensity Modulation, Penumbra, Quality Assurance


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

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