ESTRO 2023 - Abstract Book

S655

Monday 15 May 2023

ESTRO 2023

risk volumes (i.e. brainstem, spinal cord, optic chiasm, lens, temporal lobes and optic nerves), internal carotid arteries (ICA) and the nasopharyngeal (NP) mucosa were evaluated. Results HA plans significantly improved target volume coverage (GTV D95%: +9.9%, CTV D95%: +11.5%, PTV D95%: +12.1%) while achieving dose escalation by delivering higher average mean dose to target volumes (PTV: +6.8%, CTV: +6.8%, PTV: +5.5%). The HA plans were also associated with better quality in terms of PTV V100%, CI, high-dose spillage and GI without a significant difference in HI. Moreover, HA plans delivered significantly lower average maximum dose (Dmax) to spinal cord (-1.94Gy), brainstem (-3.34Gy), optic chiasm (-1.05Gy), left temporal lobe (-4.73Gy), encapsulated ICA (-0.88Gy) and non- encapsulated ICA (-12.8Gy). However, HA was also associated with a significantly higher Dmax to bilateral lens (+1.47Gy) and NP mucosa (+5.4Gy). Conclusion HA is dosimetrically feasible in re-irradiating rNPC patients with less under-dosage of target volumes when compared with IMRT. However, it must be reiterated that given the high-dose hotspots within the target volumes, high dose delivered to the NP mucosa and high fatality rate of carotid blowout, HA must be used with stringent patient selection and detailed dosimetric evaluation. OC-0785 Organized peer reflection to improve sustainable treatment planning competencies for lung cancer M. de Rooy 1 , C. Meevissen-Dijcks 1 , P. Simons 1 , B. Hanbeukers 2 , R. Canters 2 , W. van Elmpt 1 , M. Bogowicz 1 1 Department of Radiation Oncology (MAASTRO), GROW – School for Oncology and Reproduction, Maastricht University Medical Centre+, Maastricht, The Netherlands; 2 Department of Radiation Oncology (MAASTRO), GROW – School for Oncology and Reproduction, Maastricht University Medical Centre+ , Maastricht, The Netherlands Purpose or Objective The number of artificial intelligence applications in radiotherapy treatment planning (TP) is growing. This results in different required competencies and less opportunities in daily practice to keep up the complex TP skills. In this project, we evaluated if in-depth reflection among peers could improve TP skills in a sustainable way. Materials and Methods A group of 12 RTTs with variable level of experience in TP for lung cancer (3 months–20 years) was asked to create a plan (T0) for stage III non-small cell lung cancer patient according to our standard clinical protocol (30x1.5Gy). The results were discussed in detail among the RTTs in a peer session using a plan QA tool. In this tool, dosimetric and technical parameters can be plotted for a group of participants and compared to an expert. This improves objectivity and due to visual representation facilitates detailed reflection on clinical decision making among RTTs (Fig. 1). During the peer session, discussion focused on: differences in DVH and technical parameters, priorities in the optimization box and reasons behind those choices. After the peer, RTTs created a plan for a different patient (T1), with similar anatomy and tumor stage, to see how well the skills they learnt were transferred to another case. This plan was repeated after 6 months (T2) to evaluate sustainability of competencies. DVH parameters of the RTTs’ plans were compared to expert plans. Different timepoints were compared: T0-T1 and T1-T2. For the relevant DVH parameters and pairs of timepoints, differences in agreement among the group (GA) and with the expert (EA) were tested using Flinger and Wilcoxon tests (p-value<0.05), respectively. In addition, the RTTs were asked on their perception and experience of the peer session.