ESTRO 2020 Abstract Book

S521 ESTRO 2020

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, HER2-negative, tumor histological grade G1-G2, R0

resection, staged pT1-T2 pN0 cM0, with an adequate dosimetric study. A dose of 40Gy was delivered in 15F (2.67Gy/F) followed by a boost to the tumor bed of 10- 16Gy in 5-8F (2.0Gy/F). Acute toxicity (CTCAE5.0 scale) and heart and lung dosimetric parameters were recorded. Survival analysis by the Kaplan-Meier method. Results Of the 215 patients accepted for HRT, 9 were excluded. 206 included patients with a median age 64 years (50-83 years); left side tumors in 51.9%; upper quadrants in 40.8%. Invasive carcinoma not otherwise specified (NOS) present in 84.5%; stage pT1b in 33.0% and pT1c in 51.5%. A 10Gy boost was prescribed in 53.4% of patients. The median values of the dosimetric parameters evaluated were heart V25 of 3.56% (0%-19.7%) and ipsilateral lung V20 of 11.68% (1.7%-24.38%). All patients completed the initially planned schedule, 97.6% presenting acute cutaneous toxicity (any grade), grade 3 in 7.8%. No other side effects were registered during treatment. Median follow-up was 21 months (2-60 months). In the first follow- up appointment toxicity was registered in 55.8% patients, with erythema/pigmentation grade 1-2 in 17.0% and grade 3 in 1.0%, breast edema in 30.1% and scar fibrosis in 8.7%. One patient had symptomatic radiation pneumonitis, with full resolution after therapy. In subsequent follow-up appointments, there was hyperpigmentation in 7.8%, breast edema in 24.3%, scar fibrosis in 14.1% and telangiectasia in 2.9%. At two years follow-up: LRDFS 100%, DFS 99.4%, OS 98.6% and DSS 99.3%. Conclusion Hypofractionated radiation therapy allows for excellent treatment compliance with an acceptable toxicity profile. Oncologic outcomes and late toxicity results are similar to those described for conventional fractionation, making HRT a strong option in this subset of breast cancer patients in real-life settings. PO-0978 Is there a correlation between radiation doses and heart segmental alterations at 6 months? N. Fourati 1 , I. Chafaii 1 , S. Charfeddine 2 , L. Abid 2 , S. Kammoun 2 , W. Mnejja 1 , D. Jamel 1 1 Faculté de médecine Université de Sfax, Radiotherapy Oncology Department- Habib Bourguiba Hospital, Sfax, Tunisia ; 2 Faculté de médecine Université de Sfax, Cardiology Department- Hedi Chaker Hospital, Sfax, Tunisia Purpose or Objective The aim of our study was to evaluate sub-clinical cardiac alterations detected by speckle tracking echocardiography (STE) and to determine if there is a correlation between the doses received by the different segments of the left ventricle (LV) and the alterations at their level after breast cancer radiotherapy (RT). Material and Methods A total of 77 female patients with non-metastatic breast cancer were prospectively followed and evaluated. All patients received 3D conformal RT to deliver 50 Gy in 25 fractions ± 16 Gy boost. Forty seven patients (61%) had left sided RT and 71 patients (92%) received chemotherapy prior to RT. Whole LV was initially delineated and then divided into 7 different segments: the antero-basal (AB), antero-median (AM), septo-basal (SB), septo-median(SM), postero- basal(PB), postero-median (PM), and apical (A) segments. The mean dose (Dmean) of different segments was reported. All patients had STE before RT and 6 months after. A LV global longitudinal strain (GLS) alteration was defined as a reduction of more than 10% from the initial value. We then proceeded to a qualitative evaluation of the Bull’s eye alteration of different segments. Independed-sample T test was used to compare mean Dmean doses according to the alteration of the different segments.