ESTRO 2023 - Abstract Book

S737

Monday 15 May 2023

ESTRO 2023

Conclusion PelvEx II guideline adherence is high. QA meetings led to altered target volumes in over 50% of cases, highlighting the need for real-time peer-review of delineations for LRRC. The percentage of protocol deviations also shows the need for further development of the current guideline. PD-0888 Hyperfractionated re-irradiation for locally recurrent rectal cancer: A Nordic phase II trial C. Truelsen 1,2 , M. Guren 3 , A. Appelt 4 , C. Kronborg 2 , K. Spindler 1,5 1 Aarhus University Hospital, Department of Experimental Clinical Oncology, Aarhus, Denmark; 2 Aarhus University Hospital, Danish Centre for Particle Therapy, Aarhus, Denmark; 3 Oslo University Hospital, Department of Oncology, Oslo, Norway; 4 St. James University Hospital, Department of Medical Physics and Engineering, Leeds, United Kingdom; 5 Arhus University Hospital, Department of Oncology, Aarhus, Denmark Purpose or Objective The treatment of locally recurrent rectal cancer (LRRC) is challenging as excessive surgery is often needed to obtain radical resection. Neoadjuvant radiotherapy (RT) has been introduced to improve rates of radical surgery. However, patients with LRRC have often received RT as a part of the primary treatment strategy. Pelvic re-irradiation (re-RT) has proven feasible mainly in retrospective series, but it may increase the risk of acute and late toxicities. We conducted the first prospective study to evaluate re-RT with modern hyperfractionated intensity-modulated radiation therapy (IMRT) in previously irradiated LRRC patients. The primary endpoint was a radical resection (R0) rate of 50 %, and secondary endpoints included recurrence-free survival (RFS), overall survival (OS), and toxicity. Materials and Methods Previously irradiated patients with potentially resectable LRRC were included in a prospective, multicentre, phase II trial from 2015 to 2019. Re-RT was delivered with hyperfractionated, accelerated IMRT using 40.8 Gy in 1.2 Gy twice daily guided by cone-beam CT ± concomitant capecitabine 825 mg/m2 BID. Primary RT plans supported re-RT planning according to the ALARA principle for normal tissue. Re-evaluation of resectability was performed 4-6 weeks after re-RT, surgery was performed within 3 weeks when feasible. Toxicity was graded according to NCI-CTCAE (version 4.0) acute (during RT), post- RT (from the end of RT to surgery), and post-OP (within 6 months from surgery). Results Sixteen patients were included (median age: 68 years, male: 9, female: 7, performance status 0-1: 93.8 %). Median primary RT dose was 50 Gy, (range 25-60 Gy). Median re-treatment interval was 3.74 years (95 %CI: 2.73-4.73). Median re-RT dose was 40.8 Gy (range, 37.2-45). After re-RT 68.8 % (n=11) patients underwent surgery. R0 was obtained in 27.3 % (n=3/11),