Influence of target coverage priority levels on dose homogeneity in commercial automated field-in-field planning for breast radiotherapy.

To evaluate the impact of five automated field-in-field (Auto FIF) priority levels in RayStation on dosimetric parameters in left-sided whole-breast radiotherapy. Ten women with early-stage left-sided breast cancer were planned with standard tangential fields and Auto FIF at priority levels 1-5 in deep inspiration breath hold. The evaluated metrics were CTV_eval D98% and D2%, homogeneity index (HI), and ipsilateral lung V40Gy. CTV_eval D98% remained close to the prescription dose across all priority levels, whereas higher priority levels increased CTV_eval D2% and HI, indicating more pronounced high-dose regions and reduced dose homogeneity. Ipsilateral lung V40Gy increased at higher priority levels, but high-dose lung volumes remained small. Higher Auto FIF priority levels yielded only minimal gains in target coverage while increasing high-dose regions and reducing dose homogeneity. Priority levels 1 and 2 provided the most favorable balance between target coverage and organ-at-risk sparing.