ESTRO 2025 - Abstract Book

Brachytherapy - Gastro-intestinal, paediatric brachytherapy, miscellaneous

S182

ESTRO 2025

Purpose/Objective: Papillon contact radiotherapy is a minimally invasive endocavitary technique delivering targeted dose escalation to improve tumor control while preserving organ function in rectal cancer patients. Between January 2015 and October 2024, we treated patients with curative organ-preserving intent using this approach as boost to radiochemotherapy (RCT) or Total neoadjuvant radiochemotherapy (TNT). This study evaluates initial tumor response, organ preservation and treatment tolerance. Additional outcomes included local regrowth, distant recurrence and overall survival. Material/Methods: We retrospectively analyzed 104 rectal cancer patients treated with Papillon. For this analysis, we selected patients with a minimum six-month follow-up who received curative treatment as a boost to primary radiochemotherapy (n=33), total neoadjuvant therapy (n=8, including n=3 with oligometastatic disease), or salvage therapy after relapse following radiochemotherapy (n=4). Patients treated in palliative, adjuvant, or pre-surgery settings, or lost to follow up, were excluded.Primary endpoints were local response at three months post-treatment and organ preservation rates. Secondary endpoints included local regrowth rates, distant recurrence, and overall survival. Acute and late toxicities were assessed both at treatment completion and at follow-up intervals of 3–6 months Results: Among patients treated upfront with Papillon, all achieved clinical complete response (cCR) at three months. During follow-up four patient experienced local relapse, all of whom underwent curative salvage surgery: local excision (n=1), sphincter-saving surgery (n=2), and amputation (n=1). Pathological confirmation of local regrowth was obtained in 3 of 4 patients, while one showed no evidence of recurrence. After a median follow-up of 40 months, organ preservation was achieved in 42 of 45 patients (93%), including 17 (38%) with durable preservation beyond two years and 8 (18%) beyond five years. Among the four salvage cases, remission was achieved in two. Two patients died from non-cancer-related causes, and two developed distant metastasis without local relapse. Papillon therapy demonstrated excellent tolerability, with mild side effects resolving within three months. No Grade 3 or severe toxicities were reported Conclusion: Papillon contact radiotherapy confirms its pivotal role as a cornerstone in organ-sparing strategies for rectal cancer. This study highlights its efficacy and safety in achieving substantial tumor control with minimal morbidity, representing a significant advance in rectal cancer management in Switzerland. These findings underscore the potential of Papillon therapy to be widely adopted as a standard in curative organ-preserving protocols, offering an alternative to invasive surgical interventions for carefully selected patients

Keywords: Organ Preservation Rectum

2541

Digital Poster Development and Validation of a Novel Clinical Prediction Model for Contact X-ray brachytherapy in Rectal Cancer Patients Muneeb U Haq 1,2 , Mark Pritchard 1 , Arthur S Myint 2 , Ngu W Than 1,2 , Carrie Duckworth 1 , Raj Sripidam 2 , Mohammad A Javed 3 , Shakil Ahmed 3 , David M Hughes 4 1 ISMIB, University of Liverpool, Liverpool, United Kingdom. 2 Brachytherapy Department, Clatterbridge Cancer Center, Liverpool, United Kingdom. 3 Colorectal Surgery, Royal Liverpool, Liverpool, United Kingdom. 4 Department of Health Data Science, University of Liverpool, Liverpool, United Kingdom