ESTRO 2024 - Abstract Book

S2937

Interdiscplinary - Other

ESTRO 2024

to facilitate highly conformal dose administration, while sparing healthy surrounding tissue. The purpose of this study is to conduct a patterns-of-care analysis of cardiac MRgRT treatments through a survey of users of the 1.5T Unity MR-linac (Elekta AB, Sweden) that treated patients with cardiac tumors.

Material/Methods:

A survey (6 sections, 30 questions) was developed inspired by the RATING-framework[4] and STOPSTORM.eu consortium survey[5]. Our survey included questions concerning the patient cohort, imaging modalities, treatment planning/simulation, radiotherapy treatment and outcome. The collaborators were asked to score the used MRI images according to a 4-point Likert-scale and provide feedback regarding future treatment improvements.

Results:

Six international institutes (AUS 2x, USA 2x, NL 1x, TUR 1x) completed the survey reporting a total of 11 cardiac radiotherapy treatments (and targets) on the Unity MR-linac between 2021-2023 (age median[range]:59[16-81] years, male/female: 7/4, median[range] GTV: 17.7[4.1-186.6] cc, primary/metastasis: 45%/55%). CT, PET and MR imaging were used for diagnosis in 64%, 82% and 100% of the cases, respectively. For planning, CT-sim (27% with contrast-enhancement) and MRI-sim were used in all cases. In 55% of the cases, respiratory-resolved CT were acquired (of which 33% with a compression belt), while motion mitigation was omitted for MRI-sim in all cases. In a single case, 2D cine-MRI were acquired in the planning phase for the investigation of respiratory motion. An ITV approach was used in 55% of the cases (of which 33% with compression belt). The resulting treatment plan characteristics captured in this survey are represented in Figure 1. The median[range] dose per fraction was 6[5 10] Gy. The median [range] number of segments in the resulting treatment plans was 82[50-136]. The treatment plans were mainly calculated in Monaco v5.4 or higher with a dose calculation uncertainty of 1% per plan, except for a single plan that was calculated with an uncertainty of 3% per control point, on grid sizes between 2-3 mm. A single institute used MIM (MIM Software Inc., Cleveland, OH, USA) for contouring tasks. The target dose levels were not met in 18% of the cases for organs-at-risk sparing purposes.