ESTRO 2020 Abstract Book

S505 ESTRO 2020

Results As all created plans were satisfying DVH dose constraints for PTV and OARs, the main parameter used to estimate impact on DIBH treatment was BOT per fraction (table 1).

Brazil ; 2 Hospital Sírio-Libanês, Department of Clinical Oncology, Brasilia, Brazil ; 3 Hospital Sírio-Libanês, Department of Clinical Oncology, Sao Paulo, Brazil ; 4 Instituto do Câncer do Estado de São Paulo ICESP - Faculdade de Medicina da Universidade de São Paulo FMUSP, Department of Obstetrics and Gynecology - Division of Breast Surgery, Sao Paulo, Brazil Purpose or Objective The aim of this study was to determine whether there were differences in survival outcomes of matched breast cancer patients undergoing breast-conserving surgery (BCS) versus mastectomy that received neoadjuvant chemotherapy (NAC). Material and Methods A retrospective cohort of patients with stage I-III breast cancer treated between 2008 and 2014 at two institutions who had received NAC followed by surgery and post- operative radiation therapy was identified. Kaplan-Meier and multivariate Cox proportional hazards models were used to examine disease-free survival (DFS) and overall survival (OS) rates by surgery type. Results Of 652 patients, 162 (24.9%) underwent BCS and 490 (75.1%) underwent mastectomy /adenomastectomy. Most of the patients (n=589, 91.1%) had locally advanced disease (clinical stage IIB to IIIC) with a mean age of 50 years. In regards of surgery type, patients with stage III disease underwent more mastectomy them BCS (n=383, 79.0% mastectomy versus n=81,50.3% BCS; p<0.001). The DFS and OS rates for all patients at 3 years were 81.5% and 67.5% (p=0.001); 88.9% and 83.9% (p=0.174) for BCS and mastectomy groups, respectively. Despite these differences, in the multivariate analyzed adjusted by clinical stage and pathologic complete response, there were no statistical differences in DFS (mastectomy versus BCS HR 1.44; 95% CI 0.95 - 2.17) and OS (mastectomy versus BCS HR 1.03; 95% CI 0.60 - 1.75) between the surgery type. Conclusion In breast cancer patients who underwent NAC and post- operative radiation therapy, BCS and mastectomy are effective with similar survival outcomes regardless of surgery type PO-0946 Clinical impact of FFF-VMAT combined with DIBH for breast cancer radiotherapy D. Mychko 1 , A. Zverava 1 , S. Siamkouski 1 , P. Dziameshka 2 1 Minsk city Oncological Center, Radiotherapy department, Minsk, Belarus ; 2 N.N. Alexandrov National Cancer Centre of Belarus, Radiotherapy, Lesnoy, Belarus Purpose or Objective Application of flattening filter free (FFF) beams in radiotherapy (RT) has promise of potential beam-on time (BOT) reduction especially for RT techniques demanding active patients’ involvement in the process. The current study is focused on comparative evaluation of deep inspiration breath-hold (DIBH) 3D-CRT, IMRT, VMAT, FFF- VMAT techniques. Material and Methods 80 left-sided breast cancer female patients were included in the study. The patients underwent physical examination and echocardiography before and after RT as well as NT- proBNP serum level was measured. 3D-CRT, IMRT, VMAT, FFF-VMAT plans (50Gy in 2Gy per fx, 5fx/week) were generated for each patient. Dosimetric criteria for PTV and OARs were evaluated for 320 plans applying QUANTEC and ICRU recommendations. Based on planning statistics BOT was also measured and analyzed. Statistical tests (Friedman and Nemenyi) were conducted on comparisons (p < 0.05).

Statistical analysis showed significant differences between all compared techniques for this parameter (р<0.001). BOT difference between compared RT techniques was measured to evaluate the FFF-RT treatment session duration benefit. Medians of BOT difference value (s) for 3D-CRT vs. IMRT, VMAT and FFF-VMAT are listed in table 2.

Taking into account the average breath-holding cycle duration (30s) FFF-VMAT and 3D-CRT were defined as equal regarding BOT. IMRT implementation increased BOT by 74.8%, 65.9% and 54.2% (р<0.001) comparing with 3D-CRT, FFF-VMAT and VMAT and prolonged treatment session from 7 to 4 breath-holding cycles respectively. Advantage of FFF-VMAT over VMAT and IMRT at least for one breath- holding cycle was revealed and dose delivery time reduction by 24.7% and 65.9% (р<0.001) respectively was showed. For 14 patients FFF-VMAT was chosen to be a treatment option because of lower OAR doses and BOT compared to other RT techniques. The patients were under observation from 3 to 9 month after RT. The signs of G2 skin toxicity and cardiac function deterioration were not found. Conclusion BOT should be taken into account for RT session time optimization and active breathing control treatment tolerance improvement. FFF-VMAT usage leads to dose delivery time decrease with no evidence of plan quality degrading and early toxicity increasing.