Feasibility of MPC enhanced couch as SRS/SBRT Pretreatment QA

Purpose: The purpose of this study was to investigate the feasibility of using the Winston-Lutz (WL) interchangeability with a Machine Performance Check-enhanced couch for pretreatment quality assurance (QA) of stereotactic radiotherapy (SRS) and stereotactic body radiation therapy (SBRT). The study employed the MPC with an electronic portal imaging device (EPID) to carry out geometric checks and verify the radiation isocenter. The isocenter size was assessed using the MultiMet cube and the MPC-enhanced couch module for SRS/SBRT pretreatment QA. Methods: The isocenter size of the MPC-enhanced couch module was compared to the WL measurements of the MultiMet cube. Measurements were taken at various gantry, collimator, and couch angles over a period of one month. The data from the cube were evaluated using PIPSRO and MultiMet (MMWL), including the offset targets. Various statistical tests were performed to evaluate the agreement, normality, separability, sensitivity, and specificity between the two methods. Results: The results showed isocenter sizes of 0.273 ± 0.065 mm, 0.293 ± 0.010 mm, and 0.209 ± 0.070 mm for PIPSPRO, MPC, and MMWL, respectively. The average bias was -0.0639 ± 0.1061 mm between MMWL and PIPSPRO, -0.0837 ± 0.0688 mm between MMWL and MPC, and 0.0198 ± 0.0696 mm between MPC and PIPSPRO. A Shapiro-Wilk test revealed no significant departure from normality for all tests and showed satisfactory discrimination through the area under the curve (AUC). A paired t-test analysis revealed a statistically significant difference between the mean isocenter size of the MPC and WL (MMPWL: t = 5.654, df = 29, p < 0.001; PIPSPRO: t = -1.483, DF = 29, p = 0.1488), and there was no significant difference within the WL test (t = 3.008, DF = 29, p = 0.0054). Conclusion: Despite the statistical test results, there was agreement between the MPC and WL radiation isocenter size that was within the requirement of the AAPM TG 142 tolerance (±1.0 mm). The MPC proved to be accurate, reproducible, and consistent throughout the measurements, making it an appropriate and effective pretreatment QA tool for SRS/SBRT.