ESTRO 2024 - Abstract Book

S1559

Clinical - Lower GI

ESTRO 2024

[8] Gambacorta MA, Masciocchi C, Chiloiro G, et al. Timing to achieve the highest rate of pCR after preoperative radiochemotherapy in rectal cancer: a pooled analysis of 3085 patients from 7 randomized trials. Radiother Oncol. 2021;154:154-160. [9] Francois Y, Nemoz CJ, Baulieux J, et al. Influence of the interval between preoperative radiation therapy and surgery on downstaging and on the rate of sphincter-sparing surgery for rectal cancer: the Lyon R90-01 randomized trial. J Clin Oncol. 1999;17(8):2396.

2890

Mini-Oral

Neoadjuvant chemoradiotherapy and hyperthermia for locally advanced rectal cancer

Adela Ademaj 1,2 , Oliver J. Ott 3 , Cihani Gani 4 , Olav Mella 5,6 , Emsad Puric 1 , Benjamin Frey 3 , Manfred Schmidt 3 , Dietmar Marder 1 , Olaf Timm 1 , Roger A. Hälg 1,7 , Hans Crezee 8,9 , Rainer Fietkau 3 , Oliver Riesterer 1 1 Cantonal Hospital Aarau, Centre for Radiation Oncology KSA-KSB, Aarau, Switzerland. 2 University of Zürich, Doctoral Clinical Science Program, Medical Faculty, Zürich, Switzerland. 3 Universitätsklinikum Erlangen, Friedrich Alexander-Universität Erlangen-Nürnberg, Department of Radiation Oncology, Erlangen, Germany. 4 Universitätsklinikum Tübingen, Department of Radiation Oncology, Tübingen, Germany. 5 Haukeland University Hospital, Department of Oncology and Medical Physics, Bergen, Norway. 6 University of Bergen, Medical Faculty, Institute of Clinical Science, Bergen, Norway. 7 University of Zürich, Institute of Physics, Science Faculty, Zürich, Switzerland. 8 Amsterdam UMC, University of Amsterdam, Cancer Center Amsterdam, Department of Radiation Oncology, Amsterdam, Netherlands. 9 Cancer Center Amsterdam, Cancer Biology and Immunology, Treatment and Quality of Life, Amsterdam, Netherlands

Purpose/Objective:

The aim of this study is to investigate the effect of combining deep regional hyperthermia (HT) with neoadjuvant chemoradiotherapy (CRT) in locally advanced rectal cancer (LARC) patients and to understand the impact of thermal dose expressed as cumulative equivalent minutes (CEM43) on clinical outcomes.

Material/Methods:

In this multinational retrospective study, 257 LARC patients treated at four clinical centers between April 2003 and March 2020 according to specific study protocols or clinical center guidelines were included. All patients were treated with a total radiotherapy dose of 45-56 Gy in combination with concomitant chemotherapy (54% with 5 FU only) and a median of 7 HT sessions (range:1-11). Patients were subdivided into "low" CEM43 and "high" CEM43 groups by the HT session with median CEM43 <3.5 min and ≥ 3.5 min, respectively. The primary outcome was pathological complete response (pCR), secondary outcomes were local progression free survival (LPFS), disease free survival (DFS), overall survival (OS) and overall acute toxicity. We compared the oncological outcomes between "low" and "high" CEM43 groups by applying propensity scores through full matching within a caliper of 0.2 and nearest neighbor matching within a caliper of 0.4 for obtaining similar covariate distribution between treatments groups. The estimand was the average treatment effect of the treated (ATT) and it was estimated as a conditional odds ratio for both methods (full and nearest neighbor). The Chi-squared test was used to test the pCR rate difference after surgery and conditional odds ratios (ORs) with 95% CI between the two matched