S693
Clinical – Lower GI
ESTRO 2026
University Medical Center, Leiden, Netherlands. 8 Department of Pelvic Cancer, Karolinska University Hospital, Stockholm, Sweden. 9 Department of Radiation Oncology, Karolinska University Hospital, Stockholm, Sweden. 10 Department of Oncology and Pathology, Karolinska Institutet, Stockholm, Sweden. 11 Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden Purpose/Objective: Radiotherapy quality control is important, because protocol deviations may affect oncological outcomes.1 In the RAPIDO trial, short-course radiotherapy with chemotherapy (total neoadjuvant treatment [TNT]) lowered the distant metastasis rate, and increased the pathological complete response rate compared with chemoradiotherapy (CRT). However, a higher locoregional recurrence (LRR) rate was found after TNT. We investigated the quality and the influence of radiotherapy on LRR rate and localization in relation to the CTV. Material/Methods: Patients with high-risk locally advanced rectal cancer received either preoperative 5x5 Gy followed by 6xCAPOX/9xFOLFOX4 (TNT) or 25-28x1.8-2 Gy with concomitant capecitabine (CRT), optionally followed by postoperative chemotherapy. Radiotherapy data, follow-up imaging, and verification protocols were retrospectively collected. Target volume, planning/delivery and verification factors (Table 1) were compared between groups, and the influence on LRR was assessed with competing risk Cox-regression models. The location of the LRRs in relation to the CTV (in-field, borderline, or out-of-field) was investigated. Results: Of 462 eligible TNT patients, treatment planning and verification data were available for 299 and 380, respectively. For CRT patients (450), corresponding numbers were 265 and 364. GTV and CTV structures were used in 83% and 86% of the TNT, and 85% and 84% of the CRT patients. Median GTV, CTV, and PTV were similar between groups. Insufficient PTV coverage (V95Gy < 95%) was observed in 3 patients from the TNT group (V95Gy was 89%, 94%, and 94%). The distal CTV border, mandated to be 4 cm below the GTV (anal sphincter involvement was allowed), was < 4 cm in 69% (median 3.5 cm, IQR=2.5-4.2) and 63% (median 3.4 cm, IQR=2.9-3.5) of respectively the TNT and CRT patients with sphincter-preserving surgery. Treatment verification was performed according to protocol, i.e., online (TNT) or at least weekly (CRT), in 82% (TNT) and 100% (CRT). No evaluated radiotherapy factor was associated with LRR or with the difference in LRR between groups. Radiotherapy and follow-up imaging data were available for 49/70 (70%) LRR patients. LRRs were scored as ‘in-field’ in 28/33 (TNT, 85%) and 10/16 (CRT,
treatment modalities (p = 0.521). DRS related to RT was correlated with FoP ( ρ = 0.30, p<0.001), FoR ( ρ = 0.34, p<0.001), and psychological distress ( ρ = 0.34, p<0.001). Conversely, DR was negatively correlated with social support ( ρ = − 0.23, p = 0.004), PDM ( ρ = − 0.30, p<0.001), physical functioning ( ρ = − 0.47, p<0.001), and QoL ( ρ = − 0.44, p<0.001). Furthermore, primary tumor location (p = 0.006), highest educational attainment (p = 0.007), and occupational status (p = 0.001) were significantly associated with DR in univariate analyses. DR did not differ significantly between organ-preserving and trimodal treatment (p = 0.129). In multivariable regression, lower global QoL ( β = –0.288, p<0.001) and PDM ( β = –0.175, p = 0.022) were independent predictors of DR. Sensitivity analyses suggested associations with FoP and occupational status, but these were not retained in broader models. Conclusion: More than two thirds of patients reported some level of DR after multimodal rectal cancer treatment, with over 30% indicating strong DR, underscoring the relevance of this outcome in rectal cancer. DR was independently associated with worse QoL and lower PDM. Future studies should further explore predictors of DR in larger and longitudinal cohorts and evaluate targeted interventions aimed at reducing DR and patients’ participation in treatment decisions. References: Brehaut JC et al. Validation of a Decision Regret Scale. Med Decis Making. 2003;23(4):281–92. Keywords: patient-reported outcomes, survivorship Quality control and the influence of radiotherapy on locoregional recurrences in the RAPIDO trial Max D. Tanaka 1 , Ilaria Prata 2,3 , Bastiaan W. K. Schipaanboord 1 , Sanne Conijn 1 , Boudewijn van Etten 4 , Geke A. P. Hospers 5 , Corrie A. M. Marijnen 1,6 , Elma Meershoek-Klein Kranenbarg 7 , Per J. Nilsson 8 , Annet G. H. Roodvoets 7 , Alexander Valdman 9,10 , Cornelis J. H. van de Velde 7 , Bengt Glimelius 11 , Alice M. Couwenberg 1 1 Department of Radiation oncology, Netherlands Cancer Institute, Amsterdam, Netherlands. 2 GROW, School for Oncology and Reproduction, Maastricht University, Maastricht, Netherlands. 3 Department of Surgery, Netherlands Cancer Institute, Amsterdam, Netherlands. 4 Department of Surgery, University Medical Center Groningen, Groningen, Netherlands. 5 Department of Medical Oncology, University Medical Center Groningen, University of Groningen, Groningen, Netherlands. 6 Department of Radiation oncology, Leiden University Medical Center, Leiden, Netherlands. 7 Department of Surgery, Leiden Proffered Paper 1144
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