ESTRO 2024 - Abstract Book

S1523

Clinical - Lower GI

ESTRO 2024

Malicki J, Castro CL, Fundowicz M, Krengli M, Llacer-Moscardo C, Curcean S, et al. IROCA-TES: Improving Quality in Radiation Oncology through Clinical Audits — Training and Education for Standardization, Rep Pract Oncol Radiother, DOI: 10.5603/RPOR.a2023.0035.

1793

Mini-Oral

The role of concomitant boost in chemoradiation for rectal cancer; a randomized clinical trial

Mahdi Aghili, Forouzan Nourbakhsh, Mohammad Babaei, Marzieh Lashkari, Reza Ghalehtaki

Tehran University of Medical Sciences, Radiation Oncology, Tehran, Iran, Islamic Republic of

Purpose/Objective:

The standard treatment for locally advanced rectal cancer (LARC) includes a combination of chemoradiotherapy (CRT) and surgery. However, there is growing evidence that intensification of radiotherapy doses may improve oncologic outcomes. The primary objective of this study was to evaluate the effectiveness of intensified CRT compared with conventional CRT.

Material/Methods:

Patients with LARC (MRI defined cT3-4 or cN+) were recruited in our study and randomized in two arms. In the conventional CRT arm, patients received a total dose of 45Gy/25 fractions in 5 days per week to the pelvis followed by an additional 5.4 Gy in 3 fractions boost to the mesorectum (total dose was 50.4 Gy in 28 fractions). In the concomitant boost arm, patients received 45 Gy in 25 fractions to whole pelvis concomitantly with 11 Gy boost to gross tumor and/or gross large nodes plus 1-cm geographical margin in 5 weekly fractions (6th day of the week). Both groups received the same capecitabine or 5FU based concurrent chemotherapy and consolidative chemotherapy by CapOx or FOLFOX regimens in the interval between termination of CRT and surgery. After 12 16 weeks after CRT, patients were evaluated for response (endoscopy and pelvic MRI) to treatment or surgery. The patients who were willing to preserve their rectum had the choice to enter watch and wait protocol. Comparison of the effectiveness and side effects of two treatment arms was performed between groups. In order to observe a 20% difference in complete response we needed 50 patients in each group. Our primary outcome was clinical or pathologic complete response (cCR or pCR) and down-staging (defined as ypT0-2N0). Our secondary endpoints include 2-year local control and overall survival. The trial design was approved by the institutional review board and ethics committee (IR.TUMS.IKHC.REC.1400.235). We registered our trial in the IRCT repository (IRCT20211108052999N1).

Results:

Between October 2021 and April 2023, 70 patients were randomly assigned to a treatment group (table 1). Thirty seven patients in the conventional and 33 patients in the concomitant boost arms. Till October 2023, 63 patients were evaluated for response including 50 patients who underwent surgery. The cumulative complete response (clinical and pathologic) was observed in 37.9% vs. 26.5% in the concomitant boost and conventional arms, respectively (Odd Ratio= 1.43, 95%CI: 0.69-2.96; p=0.24). Among resected patients, the down-staging occurred in