ESTRO 2024 - Abstract Book

S4361

Physics - Intra-fraction motion management and real-time adaptive radiotherapy

ESTRO 2024

2550

Digital Poster

Analysis of contouring methods in online treatment adaptation of intermediate risk prostate patients

Naiara Fuentemilla-Urío 1 , Victor De La Llana 1 , Santiago Pellejero 1 , Marta Barrado 2 , Mikel Rico 2 , Victor González-Perez 3

1 Hospital Universitario de Navarra, Radiofísica y PR, Pamplona, Spain. 2 Hospital Universitario de Navarra, Oncología Radioterapica, Pamplona, Spain. 3 Fundación IVO, Radiofísica, Valencia, Spain

Purpose/Objective:

The aim of this work is to analyze the influence of the method followed in the contouring of prostate and seminal vesicles (VVSS) structures in the daily online adaptation of a treatment plan (oART). During the whole treatment of the prostate with RT, the volume of this organ and that of the VVSS is not appreciably modified with respect to that contoured on the planning CT (pCT), so that the contoured volumes are expected to have similar sizes throughout the treatment. The volume differences during plan adaptation with respect to the reference plan indicate that extra contouring uncertainty will be introduced into the RT process, not allowing adequate margin reduction to PTV for treatment with oART

Material/Methods:

The volume of prostate and SSVV contoured on pCT is 49 ± 14 cm3 and 13 ± 6 cm3, respectively. Prostate treatments performed on a Ethos LINAC (Varian Medical Medical System, Siemens, USA) between March and September 2023 have been collected. The method used to adapt the contours to the daily CBCT was the solution offered by the Ethos system during the oART sessions.

The starting point for contour editing was based on different methods:

• Artificial Inteligence (AI): the system offers a contouring solution of the structure and the CTV (prostate) and SSVVV is created by copying that same volume. The RO modifies the prostate organs offered by AI. • Rigid propagation (RP). For the prostate, the initial contour is propagated by matching the pCT fiducials to those observed on CBCT. For SSVVS, a control volume is introduced which, during oART sessions, the system creates using deformable registration algorithms and the RO adapts the volume to the daily situation. • Deformable propagation (DP). In the case of SSVV, the volume that the system generates using deformable propagation algorithms, without RO intervention, has also been evaluated. For prostate contour we evaluated 135 fractions corresponding to 10 patients, and for SSVV 166 fractions corresponding to 9 patients. The final manual contour matching was performed by 5 different Ros, but only one RO participated in each fraction.