Multi-Institutional Study of End-to-End Dose Delivery Quality Assurance Testing for Image-Guided Brachytherapy Using a Gel Dosimeter.

PURPOSE: To quantify dose delivery errors for high-dose-rate image-guided brachytherapy (HDR-IGBT) using an independent end-to-end dose delivery quality assurance test at multiple institutions. The novelty of our study is that this is the first multi-institutional end-to-end dose delivery study in the world. MATERIALS AND METHODS: The postal audit used a polymer gel dosimeter in a cylindrical acrylic container for the afterloading system. Image acquisition using computed tomography, treatment planning, and irradiation were performed at each institution. Dose distribution comparison between the plan and gel measurement was performed. The percentage of pixels satisfying the absolute-dose gamma criterion was reviewed. RESULTS: Thirty-five institutions participated in this study. The dose uncertainty was 3.6% ± 2.3% (mean ± 1.96σ). The geometric uncertainty with a coverage factor of k = 2 was 3.5 mm. The tolerance level was set to the gamma passing rate of 95% with the agreement criterion of 5% (global)/3 mm, which was determined from the uncertainty estimation. The percentage of pixels satisfying the gamma criterion was 90.4% ± 32.2% (mean ± 1.96σ). Sixty-six percent (23/35) of the institutions passed the verification. Of the institutions that failed the verification, 75% (9/12) had incorrect inputs of the offset between the catheter tip and indexer length in treatment planning and 17% (2/12) had incorrect catheter reconstruction in treatment planning. CONCLUSIONS: The methodology should be useful for comprehensively checking the accuracy of HDR-IGBT dose delivery and credentialing clinical studies. The results of our study highlight the high risk of large source positional errors while delivering dose for HDR-IGBT in clinical practices.

[Efficient Commissioning of the Radiotherapy Treatment Planning System with the Golden Beam Data].

Commissioning of a linear accelerator (Linac) and treatment planning systems (RTPs) for clinical use is complex and time-consuming, typically 3-4 months in total. However, based on clinical needs and economics, hospitals desire early clinical starts for patients, and various studies have been conducted for shortening the preparation period. One of the methods to shorten the period is using golden beam data (GBD). The purpose of this study was to shorten the commissioning period without reducing accuracy and to simplify commissioning works while improving safety. We conducted commissioning of the RTPs before installing the Linac using GBD, and carried out verification immediately after the acceptance test. We used TrueBeam STx (Varian Medical Systems) and Eclipse (ver. 13.7, Varian Medical Systems) for RTPs and anisotropic analysis algorithm (AAA) and AcurosXB (AXB) for calculation algorithms. The difference between GBD and the measured beam data was 0.0 ± 0.2% [percentage depth dose (PDDs) ] and -0.1 ± 0.2% (Profiles) with X-ray, and -1.2 ± 1.3% (PDDs) with electrons. The difference between the calculated dose and the measured dose was 0.1 ± 0.3% (AAA) and 0.0 ± 0.3% (AXB) under homogeneous conditions, and 0.7 ± 1.4% (AAA) and 0.6 ± 1.1% (AXB) under heterogeneous conditions. We took 43 days from the end of the acceptance test to the start of clinical use. We found that the preparation period for clinical use can be shortened without reducing the accuracy, by thinning out the number of measurement items using GBD.