Heterogeneity of stereotactic radiosurgery quality across the community.

e14049 Background: Stereotactic radiosurgery (SRS) is a ubiquitous technique for the treatment of brain metastases that demands highly localized and precise dose delivery. Standardized SRS audits: testing the delivery accuracy of an SRS treatment to a standardized anthropomorphic phantom, is routinely performed by the Radiation Quality Assurance Lab, including for participants in NCI clinical trials (as IROC). As these audits are performed according to each institution’s clinical processes, we analyzed SRS audit data to characterize variability across the community. Methods: We evaluated 930 irradiations (673 institutions, 2013–2023), stratifying for delivery system (GammaKnife, CyberKnife, TomoTherapy, and LINACs) and beam collimator. Radiotherapy quality metrics were examined (Conformity (CI), Gradient Index (GI), and V12Gy), as was the radionecrosis risk (NTCP) estimated using HyTEC model. Statistical analysis utilized ANOVA for subgroup differences and independent t-tests to compare pass vs. fail cohorts. Results: The overall audit pass rate, based on criteria established by the NCI’s clinical trial network, was 87%. Delivery platform strongly influenced the quality of the treatment (Table 1), and dedicated platforms typically showed distinct strengths. Gammaknife achieved the best dose fall-off and lowest V12Gy, while Cyberknife demonstrated superior overall conformity. Standard LINAC delivery yielded slightly higher normal tissue exposure, while the TomoTherapy platform exhibited the poorest conformity (0.67) and gradients (7.37). Crucially, and unexpectedly, suboptimal plan quality (i.e., worse designed dose distributions) predicted phantom delivery failure (i.e., poorer delivery accuracy). Institutions that struggled to deliver the plan dose accurately were the same as those that designed poorer plans (irradiating significantly larger volumes of normal brain (p<0.001). This association suggest a potential double-whammy for patients that may impact patient outcomes and even clinical trial results. Conclusions: SRS plan quality is intrinsically linked to delivery platform and hardware selection, and showed substantial variability across the community. Additionally, delivery accuracy was also heterogeneous, with 13% of institutions failing to meet accepted NCI standards. The quality of the treatment plan and the quality of the treatment delivery were significantly correlated, highlighting the need for ongoing evaluation of SRS. Category Pass (%) Conformity Gradient V12Gy[cc] Technique GK 62 (98%) 0.78 ± 0.08 2.7 ± 0.3 12.0 ± 1.7 CK 71 (90%) 0.86 ± 0.08 3.7 ± 0.8 14.1 ± 3.5 Elekta 148 (82%) 0.73 ± 0.11 3.7 ± 1.2 17.0 ± 7.3 Varian 513 (88%) 0.78 ± 0.11 3.2 ± 0.8 14.6 ± 10.5 Collimator LD 329 (89%) 0.76 ± 0.12 3.5 ± 0.9 16.4 ± 12.9 HD 195 (88%) 0.80 ± 0.08 3.2 ± 0.8 13.6 ± 4.7 Cone 101 (76%) 0.74 ± 0.11 3.3 ± 1.2 14.9 ± 7.1 Fail* Total: 118 (13%) 0.74 ± 0.13 3.7 ± 1.9 18.8 ± 17.3 Pass* Total: 812 (87%) 0.78 ± 0.11 3.4 ± 1.0 14.8 ± 7.9