ESTRO 2020 Abstract Book

S502 ESTRO 2020

Purpose or Objective Predictive toxicity models in radiation therapy have to be built and validated using clinical and dosimetry data. But the data reported in medical records lacks, most of the time, of structure and therefore it is difficult to use. In our institution, five years ago, we implemented a systematic way to prospectively collect structured data related to the RT patient treatment (cofounding clinical factors, oncological information, treatments, RT specific data and follow-up information) using RedCap. The analysis of this database let us to evaluate clinical outcome of breast cancer patients after treatment and which factors are related with acute/late toxicity and progression disease. Material and Methods From May 2013, 622 breast cancer patients treated in our institution with radiotherapy (Clinac2100CD,Varian) were prospectively included in the database. For this study the mean follow-up was of 3 years. A group description is shown in Table1. Baseline patient characteristics were recorded as well as clinical breast cancer information and local outcome after surgery but prior to start RT. Dosimetry data was also automatically transferred from Eclipse TPS to the database. Acute toxicity was recorded during treatment and late toxicity on a yearly follow-up. Acute/late toxicities were evaluated following the Common Terminology Criteria for Adverse Events (CTCAE v.3.0): skin toxicity (dermatitis, hyperpigmentation) and late-fibrosis. Risk factors for skin toxicity and fibrosis were investigated, considering the maximum toxicity grade presented during the treatment for skin toxicity, and during the first 2.5- year-follow-up for fibrosis. Progression disease included local recurrence and metastasis. Risk factors for progression disease were also studied. Associations were assessed with Chi-square or Fisher’s exact test for categorical factors, and with Krustall-Wallis test for quantitative factors.

- Hyperpigmentation was significantly worse in DIBH group, in those with no sun sensitivity and Skin Phototype IV or V, and in younger patients (<60 years). - Fibrosis was significantly worse in lymph-nodal irradiation group. • Disease Progression -We found 4.4% progression rate. -We found correlated risk factors for progression: staging T, absence of progesterone and estrogen receptors expression, molecular subtype Triple Negative and no anthracyclines chemotherapy.

Conclusion Structured prospective databases provide useful knowledge about the treatment outcomes in one institution being key for quality assessment and improvement. It allows building and validating outcomes in predictive models. This study allows to a-priory identify at risk patients, who could benefit from tailored surveillance protocols for toxicity and progression. Acknowledges: This work was financed by the Spanish Association Against Cancer (AECC). PO-0940 Synchronous bilateral breast cancer irradiation: Clinical-dosimetrical outcomes with VMAT J. Gadea 1 , I. Ortiz Gonzalez 1 , J.E. Maturana 1 , R. Roncero Sanchez 1 , I. Alastuey Gonzalez 1 , J. Pardo Masferrer 1 1 Hospital Universitari Son Espases, Radiation Oncology, Palma de Mallorca, Spain Purpose or Objective Classically irradiation of synchronous bilateral breast cancer (SBBC) was performed sequentially. Nowadays Volumetric Modulated Arc Therapy (VMAT) allows us treating both breasts at the same time. The aim of this study was to evaluate dosimetrical parameters and clinical outcomes for SBBC patients receiving adjuvant radiotherapy (RT). Material and Methods From April 2016 to October 2019, 31 SBBC patients were referred to our institution and selected for the analysis. Patients were divided according to their prescription dose in four groups: Group A: 50Gy/25fx, B: 60-64Gy/25fx, C: 40.05Gy/15fx; D: 48Gy/15fx. Each breast was analyzed individually due to the dose heterogeneity among the

Results Table2 shows the significant risk factors obtained from the analysis. • Acute/Late Toxicity - Dermatitis was significantly worse in the obesity group, in boost group and in those irradiated in summer or spring.