MO-0307 Results of the remote Belgian dosimetry audits for lung SBRT

Abstract

For Eclipse users only TGI correlated with the dosimetry audit data, where a higher TGI gave poorer QA results (see Figure 2). The Pearson correlation coefficients of alanine and film dose vs TGI were r = 0.491 and 0.564 respectively. Conclusion In general, the complexity of benchmark and audit plans was found to be comparable, with no statistically significant difference in complexity observed for 4 of the 5 CMs evaluated. MDLG was significantly higher in the benchmark plans, which may be attributed to the larger target volume in this plan. This indicates the audit programme is testing plans of comparable complexity to the clinical benchmark case. TGI showed moderate correlation with the dosimetry audit results. This may be used to assess the dosimetry audit plan before measurements are undertaken to ensure that potential outliers are identified before audit measurements are undertaken. MO-0307 Results of the remote Belgian dosimetry audits for lung SBRT Purpose or Objective NuTeC is performing remote dosimetry audits for lung SBRT in Belgium using alanine/EPR and radiochromic film dosimetry. The goal is to provide an independent assessment of the dosimetric accuracy for the SBRT practice of the hospitals in Belgium. Materials and Methods The centres receive the audit material and the DICOM data beforehand. The audit consists of a series of basic tests in water and solid water and an E2E test for a lung SBRT case on a commercial lung phantom preloaded with detectors. The alanine detectors had an uncertainty of 1 %. Both detectors are calibrated in dose-to-water (Dw). Consequently the centres using Acuros had to provide the dose calculations in Dw instead of dose-to-medium (Dm). The tumour volume is simulated using a 3D printed mould filled with a silicone mixture. An alanine pellet is placed in the centre of this tumour volume. Large film detectors (EBT-XD) are placed through the target in the lung equivalent material and also on top of the lungs. The comparisons of film to plans were done using gamma analysis with global normalisation and 10 % threshold. Our alanine/EPR dosimetry was also validated by the IAEA for multiple photon beams. Results