Impact of Collimator Angle Increment on VMAT Planning for Right Breast Cancer Post Mastectomy

Impact of Collimator Angle Increment on VMAT Planning for Right Breast Cancer Post Mastectomy

Introduction: This study investigates the influence of collimator angle increment (Inc) on the treatment plan quality and efficiency of volumetric modulated arc therapy (VMAT) in patients with right breast cancer post mastectomy.

Methods: We randomly selected 23 patients who underwent right breast cancer post mastectomy. Four VMAT plans were generated for each patient using the Monaco planning system, with Inc set at 10ﾰ, 20ﾰ, 30ﾰ, and 40ﾰ (Inc10, Inc20, Inc30, and Inc40), while keeping all other parameters constant. The 20ﾰ plan (Inc20) served as the reference. Target coverage (TC), D98, conformity index (CI), dose to the ipsilateral lung (V20, V5, Dmean), and planning efficiency (number of segments and control points) were evaluated and compared.

Results: The IG30 and IG40 plans showed significantly lower TC and D98 compared to IG20 (P<0.05). The CI for IG30 and IG40 was slightly worse than IG20 (P<0.05). As Inc increased from 10ﾰ to 30ﾰ, the ipsilateral lung V20, V5, and Dmean increased significantly (P<0.05). No significant differences were observed in the dose to the contralateral lung, heart, esophagus, or brachial plexus. Planning efficiency decreased significantly with increasing Inc (P<0.05), as evidenced by a reduction in the number of segments and control points.

Conclusion: Smaller Inc values improve target coverage and reduce the dose to the ipsilateral lung in VMAT planning for right breast cancer post mastectomy. However, smaller Inc compromises planning efficiency. Considering both plan quality and efficiency, an Inc of 10ﾰ or 20ﾰ is recommended for VMAT planning in this clinical setting, especially in complex cases.