ESTRO 2020 Abstract book

S566 ESTRO 2020

unfavorable anatomy underwent radiotherapy (RT) with VMAT techniques. 34 pts received RT to whole breast in 15 fractions (total dose 40.05 Gy) and 27 pts to whole breast or chest wall plus regional lymph nodes in 25 fractions (total dose 50 Gy). A sequential boost to the tumor bed of 10-16 Gy was performed, if indicated. In 8 cases DIBH technique was performed. VMAT plans in free breathing (FB) were generated using 3 arcs (180-300°), in order to reduce the interplay effect due to dynamic delivery and breathing motion, while VMAT plans in DIBH were obtained using 6 partial arcs with a width of 12-15 degrees to limit the time of delivery per arc; a virtual 10 mm bolus helped extending the dose fluency outside the body to compensate for small changes in shape and volume due to respiration or edema. The median age of pts was 57 years (range 35-82), 26 pts (16%) had a history of heart disease; most pts received anthracycline and taxanes regimen before RT, followed by trastuzumab. In all pts, echocardiography was performed before starting RT and 1- and 6-months after the end of treatment. Dose constraints to heart were: Dmean ≤ 5 Gy, V5Gy ≤ 40%, V25Gy ≤ 8% in FB and conventional fractionation (CF); Dmean ≤ 4 Gy, V8Gy < 30%, D5% < 16 Gy in FB and hypofractionation (HF); Dmean ≤ 3Gy, V25 ≤ 5% in DIBH. Dose constraints to the LAD were Dmean ≤ 20-25 Gy in FB, Dmean ≤ 15 Gy in DIBH. Results The treatment was well tolerated in all pts. Median V95% to breast/chest wall CTV and to lymph nodes CTV was 98%, both in FB and in DIBH. In FB we obtained a heart Dmean=3.2 Gy, V8Gy= 6.8%, D5%=8.8 Gy in HF treatment and Dmean= 5 Gy, V5Gy= 32% and V25Gy=3% in CF. LAD Dmean was 10.9 Gy and 15.2 Gy, respectively. In DIBH treatment we reported a heart V25= 2% and a mean LAD dose of 7 Gy.The 1- and 6-months echocardiographic control after RT completion showed unchanged cardiac functioning parameters, in particular, no variation in the ejection fraction was detected. Conclusion The VMAT technique +/- DIBH is useful in the treatment of left breast cancer pts (especially with cardiac comorbidities and unfavorable anatomy) by ensuring an excellent target coverage and sparing heart and LAD. Long-term follow-up data are needed to assess late toxicity and clinical outcomes for this subset of pts. PO-0977 Hypofractionated external beam radiation therapy for breast cancer: real-life outcomes D. Correia 1 , B. Fernandes 1 , A. Ponte 1 , M. Marques 1 , S. Couto-Gonçalves 1 , L. Rolim 1 , I. Nobre-Góis 1 , C. Carvalho 1 , J. Casalta-Lopes 1 , M. Borrego 1 1 Centro Hospitalar e Universitário de Coimbra, Radiation oncology department, Coimbra, Portugal Purpose or Objective By administering higher than conventional dose per fraction (F), hypofractionated external beam radiotherapy (HRT) leads to reduced overall treatment time and increased treatment compliance, with greater comfort for patients, at lower costs. Several randomized controlled trials have confirmed HRT as an alternative to conventional fractionation in the adjuvant setting after breast conserving surgery (BCS), with similar outcomes regarding local control and side effects. This approach has been increasingly adopted and is considered standard in most international treatment guidelines. In this study we aim to assess toxicity, disease free survival (DFS), locoregional disease free survival (LRDFS), overall survival (OS) and disease specific survival (DSS) of HRT treated breast cancer patients after conservative surgery, in a real-life setting. Material and Methods Prospective inclusion of patients with invasive breast cancer submitted to BCS, treated in our Radiation Oncology department between March 2014 and December 2018, aged 50 years or older, hormone receptor-positive,

significant.

Conclusion Reirradiation treatments exhibited very good results regarding OS, DFS and patient toxicity, which validates our current reirradiation protocol. There were no significant differences when comparing severe vs mild toxicity with respect to EQD2 and the retreatment time interval. PO-0976 Left sided breast cancer patients and advanced radiotherapy techniques. A cardiac sparing approach. F. Cucciarelli 1 , M. Parisotto 2 , S. Costantini 1 , C. Di Carlo 1 , F. Fenu 1 , S. Di Biase 1 , L. Vicenzi 1 , M. Di Benedetto 1 , A. Maucieri 1 , M. Montisci 1 , V.E. Morabito 2 , M. Valenti 2 , S. Maggi 2 , G. Mantello 1 1 Azienda Ospedaliero Universitaria Ospedali Riuniti, Radiotherapy Department, Ancona, Italy ; 2 Azienda Ospedaliero Universitaria Ospedali Riuniti, Medical Physics, Ancona, Italy Purpose or Objective To improve target coverage and reduce dose to heart and left anterior descending artery (LAD) in left breast cancer patients (pts) with comorbidities and unfavorable anatomy using volumetric modulated arc therapy (VMAT) with or without deep inspiration breath hold (DIBH). Material and Methods Between July 2015 and May 2019, 61 consecutive pts affected by left breast cancer with comorbidities and