ESTRO 2020 Abstract book

S548 ESTRO 2020

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 patients. Toxicity was evaluated using CTCAE v.5.0 criteria. Several dosimetrical parameters were evaluated for critical organs at risk (OARs). Results Median follow-up was 15,7 months and median age was 65 years (48-81). Two patients were lost for the analysis and one was dead for non-tumor-related cause. Tumor and patients characteristics are shown in Table 1. During RT side-effects were: dermatitis G1-2 in 11(35%) patients, dermatitis G3 in 1(3%), fatigue G1-2 in 9(29%) and no more grade 3 side-effects. Among the 19 patients with at least 6 months of follow-up after RT, 16(84%) patients were asymptomatic and hyperpigmentation appeared in 3(16%). At 1 year follow-up, hyperpigmentation appeared in 3(27%) of 11 patients. All patients are alive without any sign of disease. Regarding OARs, all dosimetrical parameters were within tolerance limits. Complete dosimetrical details are shown in Table 2.

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. - 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.