ESTRO 2025 - Abstract Book

S1158

Clinical – Lower GI

ESTRO 2025

References: 1. Gay HA, Barthold HJ, O'Meara E, Bosch WR, El Naqa I, Al-Lozi R, et al. Pelvic normal tissue contouring guidelines for radiation therapy: a Radiation Therapy Oncology Group consensus panel atlas. Int J Radiat Oncol Biol Phys. 2012;83(3):e353-62. 2. Tanderup K, Pötter R, Lindegaard JC, Kirisits C, Jürgenliemk-Schulz I, de Leeuw A, et al. EMBRACE II Study protocol [Available from: https://www.embracestudy.dk/UserUpload/PublicDocuments/EMBRACE%20II%20Protocol.pdf.

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Digital Poster Radiotherapy for T1 anal cancer: Single-institution analysis including brachytherapy over 30 years Johannes Knoth, Sino Piroty-Dehbokry, Joachim Widder, Rainer Schmid Department of Radiation Oncology, Comprehensive Cancer Center, Medical University/General Hospital of Vienna, Vienna, Austria Purpose/Objective: Dose and target volumes for very early anal cancer are subject of ongoing research. This study retrospectively examines changing treatment approaches for T1 anal cancer at the Medical University of Vienna. We aimed to evaluate dose, target volumes, and techniques employed, as well as treatment outcomes, including side effects. Material/Methods: Following ethical approval, all patients having received primary radiotherapy or chemoradiotherapy for localized T1 anal cancer at the Medical University of Vienna’s Department of Radiation Oncology between 1990 and 2022 with sufficient treatment and follow-up information were included. Treatments comprised EBRT with or without brachytherapy and chemotherapy. Descriptive statistics and Kaplan-Meier curves were generated to assess actuarial overall survival (OS), disease-free survival (DFS), and colostomy-free interval (CFI) across treatment settings. Results: The analysis included 55 patients (39 women, 16 men), with a median age of 67 (32-86 years) and a median follow up of 4.5 years (0-20 years). Stages included T1N0 (78%), T1N1a (7%), T1N1b (11%), and T1N1c (4%); all with squamous cell carcinoma. Of these, 45% received concurrent chemotherapy, and 33% received brachytherapy. 3D conformal therapy was used in 66% of cases, and IMRT/VMAT in 33%. The median tumor dose was 58 Gy, with a median elective planning target volume (PTV) of 1157 cm³ and a median total treatment duration of 47 days. The groin region was treated in only 21 patients (38%), yet no recurrences were noted in this area. Locoregional recurrences occurred in five patients (9.1%), none of whom had received brachytherapy. The five-year survival rates were 85% (OS), 80% (DFS), and 100% (CFI). Grade 3-4 late toxicity occurred in six patients (10.9%), all of whom had received 3D conformal therapy. No patient required a colostomy. Conclusion: Radiotherapy or chemoradiotherapy for T1 anal cancer was effective in this cohort. Severe side effects occurred exclusively following 3D conformal therapy, but not IMRT/VMAT. The addition of a brachytherapy boost may improve local control. Avoiding elective groin treatment appears not to have increased recurrences in this selective cohort.

Keywords: Anal cancer, treatment technique, clinical outcome