ESTRO 2024 - Abstract Book

S1491

Clinical - Lower GI

ESTRO 2024

Keywords: Immunoscore,Rectal cancer, Wait-and-Watch-strategy

References:

El Sissy, C., Kirilovsky, A., Lagorce Pagès, C., Marliot, F., Custers, P. A., Dizdarevic, E., Sroussi, M., Castillo-Martin, M., Haicheur, N., Dermani, M., Loche, N., Buttard, B., Musina, A. M., Anitei, M. G., van den Berg, J. G., Broeks, A., Iseas, S., Coraglio, M., Loria, F. S., Romero, A., … Pagès, F. (2023). International Validation of the Immunoscore Biopsy in Patients With Rectal Cancer Managed by a Watch-and-Wait Strategy. Journal of clinical oncology : official journal of the American Society of Clinical Oncology, JCO2300586. Advance online publication. https://doi.org/10.1200/JCO.23.00586

723

Digital Poster

Delineation variations in RT planning of rectum cancer patients using the Swedish guideline

Emil Fredén, Johan Knutsson, Cecilia Lagerbäck, Albert Siegbahn, Pehr Lind

Södersjukhuset AB, Department of Oncology, Stockholm, Sweden

Purpose/Objective:

The present Swedish delineation guideline (GL) for rectal cancer patients treated with preoperative RT in part differs from international recommendations and leave room for some interpretation. In this study, we aim to identify possible discrepancies in the delineation of target volumes and OARs among the radiation oncologists (ROs) in our Department to further understand the need for clarification of the Swedish GL. We also evaluate how such discrepancies influence the quality of the RT treatment in terms of target coverage and dose delivered to OARs.

Material/Methods:

Target volumes (GTVT: primary tumor site and CTVN) and OARs (BowelCavity, CaudEquinaS1-S2) were independently delineated by five radiation oncologists (RO1-RO5) according to the Swedish GL for one rectal cancer patient previously treated with preoperative RT (5 Gy x 5). The CTVN structures were subsequently expanded in to PTVN volumes using a 6 mm isotropic margin. For reference we adopted the clinical volumes previously delineated during treatment planning of the patient. We evaluated the agreement between structures by computing the Dice Similarity Coefficient (DSC) according to the following definition

DSC = 2*(V ref ∩ V)/(V ref +V)

where V ref ∩ V is the volume of overlap, resulting in a DSC between 0-100%. The clinical treatment plan was further used to assess target dose coverage and dose to OARs, according to the new structures delineated by the five ROs. Finally, the structures were qualitatively (visually) assessed to identify anatomical regions with a strong need for clarification in the GL.