ESTRO 2024 - Abstract Book

S1469

Clinical - Lower GI

ESTRO 2024

210

Digital Poster

VMAT in neoadjuvant radiotherapy with S-1 for rectal cancer: preliminary data of a prospective study

Hiroshi Doi 1 , Saori Tatsuno 1 , Masahiro Inada 1 , Naoko Ishida 1 , Aritoshi Ri 1 , Yutaro Wada 2 , Takuya Uehara 1 , Tomohiro Matsuura 1 , Kiyoshi Nakamatsu 1 , Makoto Hosono 1 , Junichiro Kawamura 3 , Yukinori Matsuo 1 1 Kindai University Faculty of Medicine, Department of Radiation Oncology, Osaka-Sayama, Japan. 2 Kindai University Nara Hospital, Department of Radiation Oncology, Ikoma, Japan. 3 Kindai University Faculty of Medicine, Department of Surgery Division of Colorectal Surgery, Osaka-Sayama, Japan

Purpose/Objective:

Neoadjuvant radiotherapy (NA-RT) has been adopted as the standard treatment for locally advanced rectal cancer. Recently, total neoadjuvant treatment and non-operative management have attracted increasing attention as a treatment option for locally advanced rectal cancer. The purpose of this study was to evaluate the clinical outcomes of NA-RT using intensity-modulated radiation therapy (IMRT) with volumetric modulated arc therapy (VMAT) technique combined with oral administration of S-1 for locally advanced rectal cancer in a prospective study relevant to clinical practice.

Material/Methods:

Patients with pathologically proven rectal adenocarcinoma of clinical T3 to 4 and/ or N1 to 2 were enrolled in this prospective observational study (UMIN000044067). IMRT using VMAT was recommended in long-course NA-RT. For IMRT, the radiation dosage was calculated to deliver the prescribed dose with 95% coverage of the PTV. NA RT was performed with a fractional dose of 1.8 Gy, up to a total dose of 45 Gy, and 50.4 Gy combined with S-1 in clinical T1 to 3, and T4 disease, respectively. Short-course NA-RT of 25 Gy in five fractions was acceptable. S-1 was concurrently administered to patients undergoing long-course NA-RT. Surgery was performed 6 to 11 weeks after completion of NA-RT. Surgical procedures and systemic chemotherapy were not restricted by this study. Therefore, watch-and-wait approach including total neoadjuvant therapy was acceptable. The primary endpoint was the 2-year local control (LC) rate. Time-to-event analyses were performed from the start of radiotherapy to the emergence of the event. We excluded patients with follow-up of less than 6 months without any specific events. Radiotherapy toxicity was assessed using the Common Terminology Criteria for Adverse Events, version 5.0. In the present study, we analyzed patients who underwent long-course NA-RT for locally advanced rectal cancer using VMAT combined with S-1 administration from all prospectively enrolled patients.

Results:

Between April 2021 and May 2023, 29 patients with rectal adenocarcinoma were enrolled. One, and two patient(s) received short-course NA-RT, and NA-RT using three-dimensional conformal technique, respectively, were excluded from this preliminary analysis. Thus, a total of 26 patients receiving long-course NA-RT using VMAT combined with S-1 administration were included in the present study. Patient characteristics are shown in Table.