Comprehensive radiotherapy quality assurance analysis from individual DICOM data in the HypoG-01 phase 3 trial

Quality Assurance (QA) in radiation therapy (RT) trials is crucial. We report here the QA analysis of prospectively collected individual RT-plans in the HypoG-01 phase III trial.

HypoG-01 randomised breast cancer patients indicated for locoregional RT to 40 Gy/15 fractions/3 weeks versus 50 Gy/25 fractions/5 weeks. Volume definitions following ESTRO guidelines, and dosimetric constraints were predefined. All centres underwent a prospective QA, including systematic DICOM-RT transfer. Descriptive analyses of protocol compliance, and intra and inter-centre variations were conducted.

RT-plans from 1,093 patients (89.5% of the per-protocol population), included between September 2016 and March 2020, were retrieved from 29 centres. Overall, 610 patients underwent breast-conservation surgery, with 541 receiving a tumour-bed boost, either sequentially (69.9%) or simultaneously (30.1%). Only 76 patients (6.9%) were treated using breath-hold. Most plans (99.2%) had compliant prescribed doses. Delineation rates of pre-specified organs at risk ranged from 95.2% and 100%. Regarding treatment planning, 75.1% of the CTVp_breast, 42.9% of the CTVp_thoracic wall, 90.4% of the CTVp_tumour bed, and 67.5-87.7% of the CTVn complied with protocol constraints. For delineated OARs, constraints were met in 93.7% for heart, 81.2% for ipsilateral lung, and 63.4% for contralateral breast without obvious differences between arms; however, large intra and inter-centre variability was noted.

The observed heterogeneity in contouring and RT-planning highlights the need for rigorous QA. Our QA analysis finds comparable results in both arms, which confirms the robustness of HypoG-01 outcomes, and offers a scalable framework for the conduct of future RT trials.