Planning study and dose measurements of intracranial stereotactic radiation surgery with a flattening filter-free linac

Purpose: Flattening filter-free (FFF) beams have recently become available for radiation therapy, offering much higher dose rates but complicating treatment owing to the nonflat profile. Stereotactic treatment is one of the most evident scenarios to investigate the use of FFF beams.

Methods and materials: We present a planning study of a FFF 7-MV beam for the treatment of brain metastases using multiple noncoplanar arcs. Plan differences as compared with flat 6 MV photon fields are estimated using different measures of quality. Absolute dosimetry and fluence distribution are verified and the out-of-field dose is measured.

Results: The FFF 7-MV plans are slightly better than the flat 6-MV plans as evaluated by a number of quality indices, dose to organs at risk, and out-of-field dose, although differences may not be clinically relevant. Verification does not pose any problems.

Conclusions: The FFF 7-MV treatment plans are marginally superior to the flat-beam 6-MV plans in almost all cases, with greatly reduced treatment times (almost 50%).