ESTRO 2024 - Abstract Book

S1542

Clinical - Lower GI

ESTRO 2024

(2) Dijkstra EA, Nilsson PJ, Hospers GAP, et al.; Collaborative Investigators. Locoregional Failure During and After Short-course Radiotherapy Followed by Chemotherapy and Surgery Compared With Long-course Chemoradiotherapy and Surgery: A 5-Year Follow-up of the RAPIDO Trial. Ann Surg. 2023 Oct 1;278(4):e766-e772.

2304

Mini-Oral

Adaptive RT concomitant to oxaliplatin based chemoterapy as preoperative treatment for rectal cancer

Giorgio Purrello 1,2 , Dario Spanu 3 , Paolo Passoni 1 , Najla Slim 1 , Marco Castellano 1,2 , Stefano Arcangeli 2,4 , Monica Ronzoni 3 , Valentina Burgio 3 , Silvia Foti 3 , Sara Broggi 5 , Claudio Fiorino 5 , Ugo Elmore 6 , Riccardo Rosati 6 , Di Muzio Nadia 1,7 1 IRCCS San Raffaele Scientific Institute, Radiation Oncology, Milan, Italy. 2 Università degli studi di Milano-Bicocca, Radiation Oncology, Monza, Italy. 3 IRCCS San Raffaele Scientific Institute, Medical Oncology, Milan, Italy. 4 IRCCS San Gerardo dei Tintori, Radiation Oncology, Monza, Italy. 5 IRCCS San Raffaele Scientific Institute, Medical Physics, Milan, Italy. 6 IRCCS San Raffaele Scientific Institute, Surgery, Milan, Italy. 7 IRCCS Vita e Salute San Raffaele, Radiation Oncology, Milan, Italy

Purpose/Objective:

The standard treatment of locally advanced rectal cancer consisted of preoperative radiation therapy concomitant to fluoropyrimidines followed by surgery. Recently, total neoadjuvant therapy has shown greater efficacy in terms of increasing the rate of complete pathological response (pCR) and reducing local and systemic relapse. However, based on the proposed therapy scheme, the risk of overtreatment and side effects is not negligible. The objective of this study was to evaluate the efficacy and safety of neoadjuvant oxaliplatin-based CT concomitant to RT. In particular, we report our experience about preoperative adaptive radio-chemotherapy, previously introduced by our group [1] by delivering a concomitant boost to the residual tumour on the last 6 fractions of treatment.

Material/Methods:

Patients with histologically proven low T2N0 surely eligible for abdominal-perineal resection, T3/T4N0 or any T N+ rectal adenocarcinoma were considered. Concomitant chemotherapy consisted of Oxaliplatin 85 mg/m2 on days -14, 0, +14, and capecitabine 850 mg/m2 BID from day -14 to the end of radiotherapy (day 0 was the start of radiotherapy). From 2nd semester 2015 to December 2018 in the attempt to find a better balance between efficacy and toxicity, our medical oncologists team decided to prescribe only two cycles of oxaliplatin on day -14 and 0. Radiotherapy consisted in 41.4Gy in 18 fractions, 2.3 Gy/fraction, delivered with Tomotherapy or VMAT to the tumor and regional lymph-nodes expanded by 5 mm (PTV1) defined on simulation CT and MRI imaging. After 9 fractions (half treatment) CT and MRI were repeated for the planning of the adaptive phase: PTVadapt was generated by adding a 5mm margin to the residual tumour still visible on half treatment MRI. On the last 6 fractions, a boost of 3.1 Gy/fr delivering a total dose of 46.2 Gy in 18 fractions was delivered to PTVadapt while concomitantly delivering 2.3 Gy/fr to PTV1

Results: