ESTRO 2024 - Abstract Book

S469

Clinical - Breast

ESTRO 2024

388

Poster Discussion

CBCT-guided online adaptive radiotherapy in breast cancer patients – a prospective trial NL2021.0624

Angelique R.W. van Vlaenderen 1,2 , Koen J. Nelissen 1,2 , Judith G. Middelburg-van Rijn 1,2 , Barbara L.T. Rijksen 1,2 , Jorrit Visser 1,2 , Marjan Admiraal 1,2 , Karin N. Goudschaal 1,2,3 , Ewa Bucko 1,2 , Cassey E. Glebbeek 1,2 , Nina Bijker 1,2 , Ben Slotman 1,2 , Wilko F.A.R. Verbakel 1,2,4 , Desiree H.J.G. van den Bongard 1,2,5 1 Amsterdam UMC location Vrije Universiteit Amsterdam, Radiation Oncology, Amsterdam, Netherlands. 2 Cancer Center Amsterdam, Cancer Treatment and Quality of Life, Amsterdam, Netherlands. 3 Amsterdam UMC location University of Amsterdam, Radiation Oncology, Amsterdam, Netherlands. 4 Varian Medical Systems, Radiotherapy Solutions, Palo Alto, USA. 5 Cancer Center Amsterdam, Cancer Biology and Immunology, Amsterdam, Netherlands

Purpose/Objective:

In postoperative breast radiotherapy (RT), interfractional breast contour variations due to postoperative breast seroma, oedema, or differences in arm/body positioning can result in dosimetric deviations.[1 – 3] In approximately 10% of breast patients at our department, dosimetric deviations cannot be resolved by repositioning of arms/body and offline replanning is required. Online adaptive radiotherapy (oART) allows optimization of the treatment plan (TP) to the daily anatomy avoiding offline replanning.[4,5] In addition, oART can reduce the treatment burden for the patient and healthcare logistics compared to the conventional approach. This study aims to evaluate the introduction of oART in postoperative breast RT and the impact of manual contour adaptations on clinical (dosimetric) criteria.

Material/Methods:

The BREAST-ART trial (NL2021.0624) is a single-arm prospective trial for oART in breast cancer patients. Right-sided breast cancer patients treated with postoperative whole breast irradiation (WBI) or post-mastectomy radiotherapy (PMRT) were included. A 4-beam tangential IMRT setup was scripted in Eclipse and used in Ethos (Varian Medical Systems, Palo Alto, CA) to develop a planning template in Ethos. CTV and PTV (5mm margin) were cropped 5mm beneath the body contour. The breast/chest wall contour was used as an ‘influencer’, i.e. a structure used for structure guided target contour propagation on daily CBCT. After automatic propagation to the CBCT, the influencer structure was corrected if necessary. CTV was propagated to the CBCT using contour-guided deformable image registration, guided by the influencer, and corrected if necessary. The oART procedure was executed by radiotherapy technologists (RTTs), supervised by a radiation oncologist and medical physicist. The Wilcoxon signed rank test was used to compare dosimetry between scheduled TP (reference TP on daily anatomy) and adapted TP. An in- house developed questionnaire was used to evaluate patient’s satisfaction with the procedure. Acute toxicity (Common Toxicity Criteria Adverse Events V5.0) was evaluated at baseline, during RT, and at 1 and 3 months after RT. After completion of radiotherapy, the impact of manual corrections of the influencer/CTV on the target dose was evaluated. For each fraction in which contours were manually corrected, a second TP was generated in the Ethos test environment based on the automatically generated contours. This second plan was then evaluated dosimetrically using the manually corrected (clinical) contours to identify whether a TP optimized on automatically