Optimization of field setup for organs at risk sparing and beam on time in breast radiotherapy planning for a new volumetric modulated arc therapy based treatment technique.

Background and purpose: The limitation of volumetric arc therapy (VMAT) in breast radiotherapy has been the low dose spread, especially to the contralateral side. A new treatment technique which combines VMAT and static angle modulated ports (STAMPs), which mimic intensity modulated radiotherapy (IMRT) fields, could provide a solution for this and lower treatment times. Materials and methods: The evaluation was done retrospectively on 21 breast cancer patients where two and three arc setups of the new proposed treatment techniques were compared to VMAT plans with four split arcs. The number of STAMPs and the weighting in optimization between the arcs and STAMPs was altered in the plans. This study evaluated the dose-volume histogram parameters and beam on time of this new treatment technique compared to VMAT. Results: The new technique lowered mean dose of the contralateral breast by 29-62% but increased ipsilateral lung mean doses by 7-16%. Lower number of STAMPs along with lower weighting provided the shortest beam on times. Median beam on times with VMAT were between 131 and 139 s. The fastest setups with the new technique had median times between 110 and 114 s. Conclusions: Our findings show that the new technique has potential to significantly improve sparing of the contralateral side in breast radiotherapy. In addition, the new technique can lower beam on times compared to VMAT, but this is dependent on the number and weighting of the STAMPs. Lower STAMP weighting was found to be the best option for optimizing treatment time.