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Collimator Angle Rotation and Sub Arc Optimization (CRAO) Based VMAT Radiotherapy for Multiple Brain Metastases

S Jiuling*, Wuhan University Zhongnan Hospital, Wuhan, 42CN,

Presentations

MO-E115-IePD-F3-4 (Monday, 7/11/2022) 1:15 PM - 1:45 PM [Eastern Time (GMT-4)]

Exhibit Hall | Forum 3

Purpose: To evaluate the dosimetric benefits of single isocentric coplanar volume-modulated arc therapy (VMAT) for multiple brain metastases by a novel algorithm of collimator rotation angle optimization (CRAO) for sub-arc.

Methods: Twenty patients with multiple brain metastases were included in this study. Each patient was scheduled to undergo single-center coplanar VMAT radiotherapy based on either the new CRAO algorithm or the conventional VMAT with full arc approach. In the CRAO algorithm, to improve conformal index (CI) and minimize the whitespace cost, a two-dimensional heat map of the CI for each sub-arc was generated according to the shape of the conformal multi-leaf collimator (MLC) at each target BEV projection. The dose-volume related parameters, radiotherapy field size, and the monitoring units (MUs) were compared under the two different algorithm groups.

Results: CRAO algorithm significantly increased the CI and HI (homogeneity index) of targets and reduced the involved dose to organs at risk such as: normal brain tissue, brainstem, lens, etc. The new algorithm also significantly optimized the field size, with corresponding fields of 82.2 ± 31.6 cm2 in the VMATCRAO vs. 121.9 ± 48.2 cm2 in the VMAT, respectively (P < 0.01). Furthermore, due to the non-homogeneous design of the sub-arc angles, the VMATCRAO showed a 10.2% reduction in MUs compared to the conventional VMAT.

Conclusion: VMATCRAO can improve the conformability and homogeneity of the targets for multiple brain metastases patients without compromising any treatment efficiency and minimize the low irradiation doses exposure to the organs at risk. The CRAO is worth promoting and applying in patients with multiple brain metastases who require radiotherapy.

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