Technical note: Patient‐specific quality assurance for multi‐target single‐isocenter SRS—A target‐specific approach

Abstract

AbstractBackgroundAs radiotherapy techniques advance, so do planning methods for multi‐target intracranial SRS cases. Multi‐target‐single‐isocenter (MTSI) planning offers high‐precision beam delivery with shortened duration. However, accommodating all targets in a single Patient‐Specific‐Quality‐Assurance (PSQA) with QA devices like SRS MapCHECK (SRS MC) is generally impractical.PurposeConsequently, we conducted PSQA, using a custom script, by relocating each Target or Neighboring‐Target‐Group (T‐NTG) relative to the beam isocenter on the PSQA device, ensuring each target's dose coverage at high precision.MethodsSRS treatment plans use 6MV–FFF beams, consisting of four Volumetric Modulated ARC Therapy (VMAT) arcs, including one full‐arc and three half arcs with couch‐kicks. A custom script calculated T‐NTG coordinates relative to the beam isocenter. QA verification plans were created for each T‐NTG, redefining the beam isocenter for precise alignment with the center of the SRS MC. CBCT images were acquired during PSQA for SRS MC alignment, and gamma‐index analysis (GIA) was performed. A single‐tail paired t‐test assessed the passing rate (PR) for 75 QA verification plans.ResultsGIA with l.0 mm/2.0% criteria for each QA plan yielded a PR > 95.5%, with an average of 98.9%. Plans achieving PR > 99.0% and > 97.0% constituted 63% and 92% of studied plans, respectively. Statistical significance was observed in a t‐test with an ideal PR value of 100%, while insignificance was found with a PR value of 99%, suggesting that PSQA for individual targets consistently approaches 99% PR. In MTSI cases using 6MV‐FFF beams, targets within the lateral dose‐fall‐off region require careful verification for acceptability. Our clinical study on individual T‐NTG relocation demonstrates that the presented PSQA methods are generally acceptable, supported by a statistically insignificant PR against a 99% PR value.ConclusionsPresented statistical analysis results indicate that the proposed PSQA approach can serve as a reliable tool in clinical settings.