ESTRO 2023 - Abstract Book

S362

Sunday 14 May 2023

ESTRO 2023

Conclusion All plans in the study were able to meet treatment planning constraints outlined in TRIUMPH-T trial. SAVI-plans showed high conformality without compromising coverage (V90%) even with a high degree of proximity to critical structures. It was noted that PTV-ratio shows a strong positive correlation with V90% of PTV-Eval, a strong negative correlation with maximum dose to CW and moderate negative correlation with maximum dose to skin and rib. Use of other predictors such as distance measure coupled with the proposed PTV-ratio can be explored as evaluation criteria to indicate plan complexity and the optimal achievable plan quality, especially coverage. OC-0457 Contact X-ray Brachytherapy as a sole treatment in selected patients with early rectal cancer N. Than 1 , A.S. Myint 2 , D.M. Pritchard 1 1 University of Liverpool, Department of Molecular and Clinical Cancer Medicine, Liverpool, United Kingdom; 2 University of Liverpool, Clatterbridge Cancer Centre, Liverpool, United Kingdom Purpose or Objective The standard management of early rectal cancer is surgical resection. Contact X-ray brachytherapy (CXB) is an alternative treatment for patients who are not suitable or refuse surgery and is usually combined with external beam radiation (EBRT) to treat possible lymphatic spread. We report clinical outcomes from a cohort of patients who, for various reasons, received CXB as the sole treatment for early rectal cancer. Materials and Methods From our Clatterbridge Cancer Centre database (2009-2019), we selected patients with early rectal adenocarcinoma (cT1- 2, cN0, cM0) and small tumour ( ≤ 3cm) who received CXB as their sole treatment. For tumours ≤ 3cm, three fractions of CXB are usually delivered initially and this is followed by EBRT for patients who have residual tumour after CXB. For selected patients with very early rectal cancer who achieved an initial clinical complete response (cCR) after CXB, we did not offer EBRT as the likelihood of lymphatic spread is <20%. In this cohort, we categorised patients into three groups based on their reasons for receiving CXB without EBRT: Group A: 12 patients who refused surgery (of whom 7 also refused EBRT); Group B: 10 patients who were not suitable for surgery due to advanced age and/or comorbidities, and Group C: 11 patients who had received previous pelvic EBRT for other conditions and were therefore not eligible for further EBRT. The CXB treatment regimen consisted of 30Gy/#, a total of 90Gy over 4 weeks and a further dose of 20Gy was added instead of EBRT for patients who still had small volume residual disease. We adopted a watch-and-wait policy for follow-up with endoscopy, digital rectal examination and MRI every 3 months in the first two years and 6-monthly in the third year. Local tumour control rate, disease-free survival, radiation toxicities and sphincter preservation were analysed. Results A total of 33 patients were included, with a median follow-up of 2.9 years [IQR:1.0-5.0]) and there were no significant differences between the groups in terms of age, gender, performance status, T stage or tumour . The initial cCR was excellent in Groups A and B (both 100%), but was significantly reduced (55%) in Group C (p=0.002). Sustained local tumour control was 83% in Group A, 90% in Group B, and 45% in Group C (p=0.30). Group A had better 5-year disease-free and overall survival rates (82% and 67%) compared to Group B (75% and 52%), and Group C (59% and 18%). The main radiation toxicity was rectal bleeding (21%), but only 6% of all patients required argon beam therapy. The overall organ preservation rate was 94% and only two patients needed a subsequent stoma. Conclusion In patients with early small rectal cancers with no suspicious lymph node spread, who are not suitable for or refuse surgery, it is feasible to offer CXB as the sole definitive treatment without EBRT. No patients relapsed with nodal tumour recurrence and only one patient developed distant metastasis during follow-up.

OC-0458 Contact x-ray radiotherapy (Papillon) for organ preservation in rectal cancer C. Picardi 1,2 , F. Caparrotti 3 , F. Ris 4 , M. Montemurro 5,6 , D. Christen 7 , L. Lestrade 8 , O. Matzinger 9,10

1 Swiss Medical Network, Clinique de Genolier, Radiation Oncology , Genolier, VD, Switzerland; 2 Hirslanden Radiotherapie, Radiation Oncology, Zürich, Switzerland; 3 Swiss Medical Network, Clinique Générale -Beaulieu, Radiation Oncology, Geneva , Switzerland; 4 Hôpitaux Universitaires de Geneve, Surgery, Geneva, Switzerland; 5 Onkozentrum Zürich, Medical Oncology, Zürich, Switzerland; 6 Swiss Medical Network , Clinique de Genolier, Medical Oncology, Genolier, Vaud, Switzerland; 7 Swiss Medical Network, Bethanien, Surgery, Zürich, Switzerland; 8 Swiss Medical Network, Radiation