Toxicity and Outcome of Whole Breast Hypofractionated Radiotherapy: a Single Institution Experience

The study is observational, homogeneous (performed in a single institution), non-interventional, and composed of two parts: one retrospective and one prospective (for which we request the registration in the register of clinical trials). The patients with breast cancer treated with adjuvant hypofractionated radiotherapy at the Department of Radiotherapy of "San Raffaele Scientific Institute" (IRCCSSRaffaele) from January 2009 will be identified and their clinical and dosimetric data retrieved and analyzed. The objectives of the retrospective arm of the study are the analysis, with a follow up of 5 years, of acute and late toxicity, and clinical outcomes, such as local and regional control, overall survival, disease free survival and cancer-specific survival. A secondary objective is the identification of prognostic factors for toxicity and disease progression. With the amendment approved by the Ethics Committee 1 of Lombardy Region in 22/05/2024 (CET Em. 195-2024) the number of patients in the retrospective arm was expanded to 3300. Were included: patients treated with moderate hypofractionated or ultra-hypofractionated radiotherapy to whole breast+/- simultaneous integrated boost to surgical bed, patients treated with accelerated partial breast irradiation, patients treated with hypofractionated radiotherapy to regional nodal irradiation and whole breast+/-SIB to surgical bed. The follow-up period was expanded to 10 years. The objective of the prospective arm of the study, for a cohort of 500 consecutive patients who agree to participate in the study, is to assess the quality of life of the patients treated with hypofractionated short course (3 weeks) radiotherapy. The quality-of-life questionnaires (QLQ) of the European organization for research and treatment of cancer (EORTC): QLQ-C30 (general) and QLQ-BR23 (specific for the breast), will be distributed before radiation treatment, at the time of patient enrollment, at the end of therapy and during the follow up visits, for a duration of 5 years after the first follow up, scheduled first at 6 months and then annually. Given the non-interventional, observational nature of the study, the follow up program of the patients with breast cancer, treated according to the standard departmental protocol, will not be modified. The patients will be identified from the patient data base from medical records retrieved from the radiotherapy archive, and the images monitoring local evolution from the photo archive. The data will be extracted from medical records. In addition, the dosimetric data of the treatments will be recovered from the physical dosimetric archives and the extrapolated data will be correlated with clinical and toxicity outcomes. For the patients of the prospective observational arm, the dosimetric data and quality of life questionnaires, as well as the follow up visit results, will be prospectively collected, registered in a data base, and subsequently analyzed. The toxicity registered during the visits carried out during the treatment will be determined using the Radiation Therapy Oncology Group (RTOG) scale; the Scoring system of late effects of radiation on normal tissues (SOMA-LENT scale) will be used for toxicity registered during the follow up visits. The clinical points analyzed will include: quality of life, overall survival, disease free- and cancer specific-survival, local and regional control, distant metastasis free survival, acute and late toxicity, physical dosimetry and aesthetic results. The correlation between detected parameters will be evaluated for the identification of prognostic factors. Statistical analyses will be performed with SPSS software version 17.0 (SPSS Inc. Released 2008; SPSS Statistic for Windows, Version 17.0. Chicago, USA: SPSS Inc.) and MedCalc v.12.1.4.0 (MedCalc Software, Ostend, Belgium) and any updated version. Statistical tests to be used will include: uni- and multi-variate logistic regression to define predictors of incidence and prevalence of toxicity and local/ distant relapses; Cox model ( proportionally-hazard regression) uni- and multi-variate for actuarial analysis of predictors of toxicity and local/ distant relapses; Wilcoxon matched -pair test for the quality of life index variations; Spearman test for the correlation between continuous variables, ANOVA test for the effect of treatment variables on changes in QoL scores over time. \*Enrollment in the quality-of-life study was suspended in November 2021 due to patients' refusal to participate during the Sars-Cov2 pandemic, the adoption of shorter schedule protocols to minimize patient hospital visits, the adoption of a simultaneous integrated boost for patients with high risk of local relapse(TNBC, HER2+) requiring a change in the technique utilized.