End to end dosimetric and geometric verification of single isocenter multitarget stereotactic radiosurgery using an anthropomorphic phantom: external audit validation.

Abstract

Our study aimed to perform a comprehensive end-to-end (E2E) dosimetric and geometric evaluation of the newly commissioned Varian Edge linear accelerator (LINAC) with the HyperArc™ VMAT system for multi-target stereotactic radiosurgery (SRS) to ensure clinical accuracy and safety in the treatment of multiple brain metastases. E2E testing was conducted using the MAX-EA anthropomorphic phantom, incorporating ion chamber and film inserts. The phantom was immobilized with a Q-fix Encompass system and scanned with a 0.625 mm CT protocol. Five spherical PTVs range between (0.3-9.2 cc) were planned using Eclipse™ v18.01 with 6 MV-FFF beams and optimized via the Photon Optimizer algorithm with Acuros XB (1.25 mm grid). A HyperArc™ plan prescribing 15 Gy to each target was generated. Ionization chamber, Gafchromic EBT-XD film, portal dosimetry (EPID), and Multi-Target Winston-Lutz (W-L) tests were used to evaluate dosimetric and geometric accuracy. The measured-to-calculated dose difference was - 3.3% for the HyperArc plan. Film analysis yielded average gamma pass rates > 94.9% (2%/2 mm), > 96.5% (3%/1 mm) and > 98.68% (3%/2 mm). Portal dosimetry achieved > 96.05% average gamma pass (2%/2 mm). The W-L test all targets demonstrated localization accuracy within 0.5 mm and MPC measurements confirmed sub-millimeter isocenter accuracy within 0.29 mm. E2E evaluation of the Edge LINAC with HyperArc VMAT demonstrated submillimeter geometric precision and robust dosimetric accuracy. Also, the Results met AAPM-RSS benchmarks. While rigid phantom validation inherently idealizes real patient-specific anatomical and setup variations. These high-quality baseline results support the clinical accuracy of the treatment workflow.