Optimizing breast and chest wall treatment planning: Integrating dynamic collimator rotation with static-angle...

RapidArc Dynamic (RAD) integrates static-angle modulated ports (STAMPs) and a dynamic collimator into arc delivery. The optimal use of RAD, including the ideal number of STAMPs, the best use of the dynamic collimator, and the ideal relative weighting between arc and STAMPs, has yet to be reported. We aim to investigate optimized utility of these parameters for breast and chest wall treatment planning to achieve superior dosimetric results.

Thirteen breast and chest wall patients were planned using RAD. Plans were created using the three different dynamic collimator options, five different arc/STAMP weighting options, and with 2, 4, and 6 STAMPs. All plans were created with automated skin flash. RAD plans were compared to conventional RapidArc (RA) plans. The DVH metrics and MUs for each plan were recorded, and a paired T-test was used to test for statistically significant (p ≤ 0.05) differences between the plans.

"Optimize between static angles" was the best option for dynamic collimator setting. Increasing the number of STAMPs from 2 to 4 or 6 lowered PTV V105% in patients where the PTV V105% was high but provided limited benefit in most patients. Selecting arc-dominant weighting yields significantly worse DVH metrics than a balanced weighting. Dosimetric differences were minimal between (0) Balanced, (1) Static, or (2) Static-Dominant weighting.

The following are recommended as a starting point for breast and chest wall RAD plans: 2 STAMPs positioned similar to breast tangents, "optimize between static angles" for the dynamic collimator, and a weighting of either (0) balanced, (1) static, or (2) static-dominant. The arc-dominant setting resulted in plans of the lowest quality.