Sci‐Fri PM: Radiation Therapy, Planning, Imaging, and Special Techniques ‐ 02: Feasibility of using multileaf collimation for stereotactic radiosurgery of arteriovenous malformation

Abstract

SRS using linac and cones offers steep dose fall‐off but a tradeoff exists between conformality and treatment time, which depends on the number of isocentres. Purpose of this study is to quantify planning metrics between cones‐ and MLC‐based SRS for arteriovenous malformation(AVM).Seven AVM cases treated with cones were re‐planned with MLC on Pinnacle treatment planning system. Planning target volume(PTV) was created with 1mm uniform margin to the AVM to account for MLC positional variation. Clinically‐planned prescription dose(15–25Gy) was used. Four plans were generated per case:non‐coplanar VMAT(ncV), single‐arc VMAT(saV), non‐coplanar IMRT(ncI), non‐coplanar conformal(ncC). Plans were compared for conformity(CI), heterogeneity(HI) and gradient(GI) indices and brain doses. Estimated treatment times and monitor units(MU) were compared.Cone‐based plans required 2–6 isocentres. Though CI‐RTOG was similar for plans(median=0.98), CI‐Paddick was most favourable for ncV(median=0.86) and worst for cones(0.54). HI for MLC plans(median=1.19–1.27) were lower than cone‐based plans(1.43). GI was similar for all plans. For 2/7 ncC had brainstem maximum dose>16.7Gy and therefore were clinically unacceptable. Brain V12Gy,V10Gy,V2Gy were lowest in the cones plan. ncV brain V12Gy,V10Gy,V2Gy were lowest of all MLC‐based plans studied. Treatment MUs were similar for MLC‐based plans and up to 70% lower than clinically delivered plans.ncV showed best conformality in this study. Of the MLC‐based plans, ncV also showed lowest normal tissue dose with reasonable treatment time.