Prescription to 50-75% isodose line may be optimum for linear accelerator based radiosurgery of cranial lesions

Purpose The prescribed percentage-isodose-line (PIDL) in linac-based SRS varies among institutions. For plans with similar tumor coverage and conformity index, the one with sharper dose falloff outside the tumor volume would be preferred because the probability of brain necrosis is related to the irradiated volume (for example V12Gy) outside the tumor. The aim of this study is to investigate the optimal isodose line that yields the steepest dose falloff for linac-based SRS using dynamic conformal arc technique (DCA).