No small matter.
Top Line: Is there a brain dose constraint comparable to the V12 for patients receiving 5-fraction SRS for brain metastases?
The Study: Brain V12 is a frequently used normal tissue constraint that is associated with radiation necrosis risk after single fraction SRS. It can be challenging to extrapolate the single fraction V12 metric for fractionated SRS. And while plan quality metrics like conformity and gradient should really drive SRS planning, some like to have normal tissue constraints to assess the risk of toxicity. In this multi-institutional retrospective study of >80 patients receiving 5-fraction SRS (mostly 30 Gy), brain V25 > 16 cc and V30 > 10 cc were associated with a significant increase in the risk of symptomatic radiation necrosis. More specifically, it was the volume of uninvolved brain (i.e. outside the target) that was associated with necrosis risk, and that risk went from 2% to >20% when both thresholds were exceeded. Such thresholds may be good indicators of the overall risk of necrosis and could also influence the choice of prescription dose.
TBL: Uninvolved brain V25 and V30 may be good measures of necrosis risk after 5-fractions SRS for brain metastases. | Andruska, Radiother Oncol 2020