ESTRO 2023 - Abstract Book

S1036

Digital Posters

ESTRO 2023

hypoFx RT has increased to 75% from 25%, and the consideration for omission of RT after breast-conserving surgery has decreased to 38% from 48% in 2017. The use of hypoFx RT for PMRT also has increased to 36% from 8% in 2017. Conclusion This survey shows high adoption of HypoFx RT after breast-conserving surgery in both invasive breast cancer and DCIS and moderate adoption of HypoFx RT for PMRT compared to 2017. Further studies to reach a consensus on applying RNI are advocated.

PO-1293 Implementation of daily online adaptive radiotherapy for post-operative whole breast irradiation

K. Nelissen 1,2 , W. Verbakel 1,2 , B. Rijksen 1 , M. Admiraal 1 , J. van der Himst 1 , E. Bucko 1 , B. Slotman 1,2 , D. van den Bongard 1,2,3

1 Amsterdam UMC location Vrije Universiteit Amsterdam, Radiation Oncology, Amsterdam, The Netherlands; 2 Cancer Center Amsterdam, Cancer Treatment and Quality of Life, Amsterdam, The Netherlands; 3 Cancer Center Amsterdam, Cancer Biology and Immunology, Amsterdam, The Netherlands Purpose or Objective During postoperative whole breast irradiation (WBI), unexpected dosimetric deviations can occur due to breast contour changes resulting from resorption of breast seroma/hematoma, oedema either postoperatively or during WBI, or arm/body positioning variation. In 10-15% of cases, repositioning after setup imaging is not sufficient, and offline plan adaptation is required. This results in 2-3 days delay in continuation of WBI. Daily online adaptive radiotherapy (OART) provides the opportunity to adapt for contour changes during treatment. Our aim is to evaluate the implementation of OART in post operative WBI. Materials and Methods The BREAST-ART study (IRB2021.0624) is a single-arm prospective trial. All patients with right-sided breast cancer referred for WBI after BCS were eligible. First, robust templates were developed for offline and online treatment planning to a total dose of 26Gy in 5 fractions with a four beam IMRT tangential beam setup. CTV breast was expanded by 5mm to PTV breast, both were cropped 5mm from the body contour. Clinical goals used in the template to create the reference treatment plan (TPR). are shown in Table 1. During the OART procedure, the influencer structures (i.e. used in target propagation) and targets were reviewed by radiotherapy technologists (RTTs) and approved by a radiation oncologist (RO). Adapted treatment plan (TPA) was evaluated by the RTTs, RO, and medical physicist before treatment. Patient experience was evaluated using in-house developed questionnaires after sessions one and five, scoring treatment satisfaction on a 4-point Likert scale. Dosimetric, DICOM images and time data was exported from the clinical systems. The Wilcoxon signed rank test was used to evaluate differences between scheduled (=TPR calculated on daily anatomy) treatment plan (TPS) and TPA. Acute toxicity was evaluated according to Common Toxicity Criteria V5.0 at baseline after WBI(n=5) up to 3 months after WBI(n=2). Results We obtained signed informed consent of five right-sided breast patients with post-operative WBI. Two patients were treated with standard skin marks for positioning, for three patients less (n=2) or no(n=1) marks were used. Patient experience scores were 3-4, median time needed for the adaptive treatment was 18.0(range:14-27)min (Figure 1). Dosimetric results of the target volumes and organs at risk are shown in Table 1. For all patients TPA was used. Influencer structures were adapted during 11, and target structures during 7 fractions. Median CTV volume increased with 4.1(-3.3 to 14)% compared to the initial volume on the planning CT. Only grade 0-1 acute toxicity was observed.