LAUSR

Simple Summary Radiation therapy (RT) is one of the corner stones of the local treatment of breast cancer (BC). Toxicity factors related to RT and their consequences are poorly known because of limited DICOM data and limited analyses on contouring, dose distribution and the RT technique. This manuscript describes the methodology used and provides the first characterization of the study population and RT data in CANTO-RT (CANcer TOxicities RadioTherapy). To our knowledge, our study is the largest available multicenter prospective multicenter cohort of early breast cancer with full DICOM RT data (files (CT, RT Structure, RT Dose, RT Plan)). This study answers to a concern about toxicity factors related to radiotherapy and their consequences and aims to identify predictors of development and the persistence of long-term toxicities in breast cancer patients. Further long-term projects (heart, lung, skin, fatigue) and follow up is ongoing. Abstract This article describes the methodology used and provides a characterization of the study population in CANTO-RT (CANcer TOxicities RadioTherapy). CANTO (NCT01993498) is a prospective clinical cohort study including patients with stage I-III BC from 26 French cancer centers. Patients matching all CANTO inclusion and exclusion criteria who received RT in one of the 10 top recruiting CANTO centers were selected. Individual full DICOM RT files were collected, pseudo-anonymized, structured and analyzed on the CANTO-RT/UNITRAD web platform. CANTO-RT included 3875 BC patients with a median follow-up of 64 months. Among the 3797 patients with unilateral RT, 3065 (80.4%) had breast-conserving surgery, and 2712 (71.5%) had sentinel node surgery. Tumor bed boost was delivered in 2658 patients (68.5%) and lymph node RT in 1356 patients (35%), including internal mammary chain in 844 patients (21.8%). Most patients (3691 (95.3%)) were treated with 3D conformal RT. Target volumes, organs at risk contours and dose/volume histograms were extracted after quality-control procedures. CANTO-RT is one of the largest early BC prospective cohorts with full individual clinical, biological, imaging and DICOM RT data available. It is a valuable resource for the identification and validation of clinical and dosimetric predictive factors of RT and multimodal treatment-related toxicities.