S1510
Interdisciplinary - Quality assurance and risk management
ESTRO 2026
Keywords: Mevion S250-FIT, proton therapy, magnetic field
Digital Poster 2131 Mind the Gap: Assessing evidence for reirradiation dose constraints in the pelvis Christopher J H Pagett 1 , Joep Stroom 2 , Myriam Ayadi 3 , Nick West 4 1 Medical Physics, Leeds Teaching Hospitals NHS Trust, Leeds, United Kingdom. 2 Radiation Oncology, Champalimaud Foundation, Lisbon, Portugal. 3 Medical Physics, Centre Leon Berard, Lyon, France. 4 Medical Physics, Northern Centre for Cancer Care, Newcastle, United Kingdom Purpose/Objective: An international working group previously published reirradiation (reRT) dose constraints from 17 radiotherapy departments, showing substantial variation in practice [1]. To improve reRT, it is important to understand the reasons for these differences. As 81% of centres derived constraints from the literature, we examined the origin of the cited sources to understand the basis for discrepancies. Material/Methods: As part of the survey on dose constraints, the literature sources were recorded, where applicable. For this initial work, we only looked at the literature quoted for pelvic organs at risk (OARs). Firstly, we compiled the references listed for each site. Evidence levels can be assessed using GRADE formulation [2] or similar systems. We used an adapted reRT-focussed scoring approach to assign a normalised score (0.00- 1.00) across ten categories (Figure 1), with three categories (study type, dose summation and reRT specificity) weighted more highly (x2.5). Each reference was scored per OAR, with results checked for agreement.
Results: A total of 11 pelvic references were quoted: bladder (n=9), rectum (n=8), small bowel (n=5), colon (n=4) (Figure 2).The scores for each reference for each organ and the average score is shown in figure 2. The average score is 0.44 (0.21-0.77) with five references having a score < 0.25.The average score for each category is shown in figure 1. The average score is 0.47 (0.20-1.00). 7 of the 10 categories had a score 0.40 including the three higher relevance categories.
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