ESTRO 2023 - Abstract Book

S736

Monday 15 May 2023

ESTRO 2023

Conclusion Our results support that MRgRT treatment with dose escalation up to 60.1 Gy on the tumour, prescribed on the basis of predicted response according to the ERI index for LARC patients, is well tolerated. We are awaiting the end of enrolment for the analysis of primary and secondary outcomes. PD-0887 Quality assurance of delineation for locally recurrent rectal cancer: PelvEx II data (NCT04389086) F. Piqeur 1,9,8 , B. Hupkens 2 , S. Nordkamp 3 , M. Berbee 4 , J. Buijsen 4 , H. Rutten 3,5 , P. Burger 6 , C. Marijnen 7,8 , H. Peulen 1 1 Catharina Hospital, Radiation Oncology, Eindhoven, The Netherlands; 2 Maastro , Radiation Oncology, Maastricht, The Netherlands; 3 Catharina Hospital, Surgical Oncology, Eindhoven, The Netherlands; 4 Maastro, Radiation Oncology, Maastricht, The Netherlands; 5 Maastricht University, GROW School of Oncology and Developmental Biology, Maastricht, The Netherlands; 6 Catharina Hospital , Surgical Oncology, Eindhoven, The Netherlands; 7 The Netherlands Cancer Institute, Radiation Oncology, Amsterdam, The Netherlands; 8 Leiden University Medical Centre, Radiation Oncology, Leiden, The Netherlands; 9 The Netherlands Cancer Institute , Radiation Oncology, Amsterdam, The Netherlands Purpose or Objective Neoadjuvant chemoradiotherapy (CRT) is used in locally recurrent rectal cancer (LRRC) to reduce tumour volume and increase chances of a radical surgical resection. Currently, delineation guidelines for LRRC are lacking. Within the PelvEx II trial, an international phase III RCT, a consensus-based delineation guideline was instated. A quality assurance (QA) programme is ongoing to evaluate guideline adherence and improve delineation homogeneity. In this study we aimed to investigate the impact of a QA programme on guideline adherence for the first 51 patients. Materials and Methods A delineation manual was distributed to all participating centres. Prior to CRT and preferably to dose planning, delineations were discussed by the treating physician and a member of the PelvEx II QA team (CM, HP, JB, MB, BH, FP) after a short case summary. This was performed via MS teams, in a 15 minute meeting, planned shortly after completing delineation, to facilitate participation and avoid treatment delay. Guideline adherence was evaluated by a standard scoring list, consisting of 13 points. During the meeting, adjustments were made if indicated. Any agreed upon guideline deviations were noted. Planning CTs were retrieved with the final contours and, if available, the contours delineated prior to the QA meeting. Guideline compliance was scored in a binary manner per guideline recommendation, and displayed as percentage per patient. Median volumes with range before and after QA were analysed. Results From 01-05-2021 to 11-10-2022, 51 QA meetings were performed in 16 centres for 34 re-irradiation and 17 RT-naive patients. A median of 3 QA meetings per centre were performed (range 1-9). Mean guideline adherence was 89.2% overall (SD 9.8%) and was not significantly different in RT-naive patients (85.9%, SD 10.8%) compared to patients undergoing re-irradiation (90.6%, SD 9.2%) (p=0.166). Most protocol violations were seen regarding target volume definition in fibrotic tumours (n=12), elective nodal delineation (n=6) and editing towards OAR (n=7). Alterations were advised in 53.1% of cases, with 58.8% in RT-naive patients and 40.6% in patients undergoing re-irradiation p=0.224). 22 changes led to an increased GTV or CTV, whereas 5 led to smaller target volumes. An example of contour alterations is shown in figure 1, regarding a recurrence located in fibrosis. Planning CTs with contours were retrieved for 43 patients. Median volumes before and after QA, with relative and absolute differences, can be found in table 1. Median CTV after QA (332cm3) was significantly larger than median CTV before QA (285cm3) (p=0.001). In 11 QA meetings (20.8%), consensus was reached to deviate from the instated guideline.