ESTRO 2023 - Abstract Book

S241

Saturday 13 May

ESTRO 2023

Conclusion Motion management technique played an important role in the passing or failing result of IROC’s thoracic phantom. In a counter-intuitive finding, the use of larger radiation fields to cover the target was associated with poorer performance in delivering the treatment as intended. Clinically, careful attention to the choice of motion management technique and its implementation is needed to ensure optimal patient care.

MO-0306 Use of plan complexity metrics for quality assurance in SBRT radiotherapy trials R. Patel 1 , A. Main 2 , P. Díez 1 , C. Clark 3,4,5

1 National Radiotherapy Trials Quality Assurance Group, Mount Vernon Cancer Centre, Radiotherapy Physics, London, United Kingdom; 2 UCL, Department of Medical Physics and Biomedical Engineering, London, United Kingdom; 3 National Radiotherapy Trials Quality Assurance Group, UCLH, Radiotherapy Physics, London, United Kingdom; 4 UCLH NHS Foundation Trust, Radiotherapy Physics, London, United Kingdom; 5 National Physical Laboratory, Metrology for Medical Physics, London, United Kingdom Purpose or Objective Complexity metrics (CM) can be used to quantify the complexity of radiotherapy treatment plans. As part of a national program for the implementation of spinal SBRT, accreditation was required for centres prior to treating clinically. The quality of spine SBRT planning was assessed with a benchmark case and safe and accurate delivery ensured through an external dosimetry audit. A pre-outlined benchmark case had to be planned to specifications set in the UK SABR Consortium Guidelines. Once approved, a treatment plan was created for an anthropomorphic spine phantom, which would be delivered in an end-to-end dosimetry audit. This study aims to use CMs to evaluate whether the level of complexity is comparable between benchmark and audit plans produced at each centre and to assess whether certain metrics could be used in the QA process to flag outliers and plans which could perform poorly in the dosimetry audit. Materials and Methods 29 UK centres’ benchmark and dosimetry audit plans were analysed using PlanAnalyzer, software developed by Hernandez et al. Some centres completed QA using multiple TPSs; in total 26 Eclipse, 13 Pinnacle, 9 Monaco, 9 Raystation and 1 Oncentra plans were evaluated. CMs were computed and five were selected for comparison: plan monitor units (MU), Modulation Complexity Score (MCS), Gantry Speed Modulation (GSM), Median Dosimetric Leaf Gap (MDLG) and Tongue and Groove Index (TGI). A Wilcoxon sign rank test was performed to test whether the two groups (benchmark and audit plans) were statistically different. For Eclipse users, a comparison was made of CMs against alanine and film dosimetry results, to determine any correlation. Results A comparison of MU, MCS, GSM, MDLG and TGI for benchmark and audit plans is displayed in Figure 1 (NB- 3 centres changed TPS between benchmark submission and audit). A Wilcoxon sign rank test only showed statistical significance for MDLG (p- values were p=0.649, p=0.524, p=0.668, p<0.001 and p=0.309 for MU, MCS, GSM, MDLG and TGI, respectively).