ESTRO 2020 Abstract book

S554 ESTRO 2020

not on the systolic function of the ventricle, although abnormal EF changes has been reported at 12 month follow up. PO-0951 Which is the best once-daily schedule for partial breast irradiation?Results of three phase-2 trials L. Vinante 1 , M. Avanzo 2 , C. Furlan 3,4 , A. Caroli 4 , A. Revelant 4 , G. Franchin 4 , S. Massarut 5 , M. Trovò 4,6 1 Centro di Riferimento Oncologico dia Aviano - IRCCS, Radiation Oncology, Aviano, Italy ; 2 Centro di Riferimento Oncologico di Aviano - IRCCS, Medical Physics, Aviano, Italy ; 3 Ospedale di Belluno, Radiation Oncology, Belluno, Italy ; 4 Centro di Riferimento Oncologico di Aviano - IRCCS, Radiation Oncology, Aviano, Italy ; 5 Centro di Riferimento Oncologico di Aviano - IRCCS, Breast Surgery, Aviano, Italy ; 6 Azienda Sanitaria Universitaria Integrata di Udine, Radiation Oncology, Udine, Italy Purpose or Objective Partial Breast Irradiation (PBI) for early-stage breast cancer has emerged as a shorter and more convenient radiation modality compared to standard whole breast irradiation. The most used PBI schedule is 38.5Gy in 10 twice-daily schedule. Once-daily schedule is a promising approach but the optimal dose is actually under investigation. We report the results, in terms of toxicity and local control, from three consecutive prospective phase-2 trials to determine the optimal fractionation schedule in PBI. Material and Methods Patients with early-stage (pT1-pT2, pN0-pN1a, M0) invasive breast cancer were enrolled after conservative surgery. The minimum age at diagnosis was 60 years old. PBI was delivered with 3D-conformal radiotherapy technique, while treatment volumes and radiation therapy planning were based on NSABP B-39/RTOG 0413 guidelines. Three different biologically equivalent schedule were tested: 40Gy/10 fractions (4Gy/fraction), 35Gy/7 fractions (5Gy/fraction) and 28 Gy/4 fractions (7Gy/fraction). Regular follow-up was performed by a radiation oncologists by clinical examination, mammography and breast/axilla ultrasound. Local control (LC) and disease-free survival (DFS) were estimated by Kaplan Meyer method, toxicity was scored with Common Terminology Criteria version 4.0 scale. Results Between 2008 and 2016, 189 patients were enrolled with a median follow-up of 60 months. 80 patients were treated with 40Gy/10 fractions schedule, 73 patients with 35Gy/7 fractions, 36 patients with 28Gy/4 fractions. The 5-year LC and DFS were 96% and 93% respectively, without significant differences between the three schedules. Six cases of acute Grade≥2 toxicity occurred, 4 (5%) in 40Gy/10 fraction group, 2 (2.7%) in 35Gy/7 fraction and 0 in 28Gy/4 fractions, p=NS. One patient in 40Gy/10 fractions group experienced Grade-3 acute pain. Seventeen cases of late Grade≥2 toxicity were detected, 4 (5%) with 40Gy/10 fractions schedule, 5 (6.8%) with 35Gy/7fractions and 8 (22%) with 28Gy/4 fractions, p=0.008. In particular the only 3 cases of late Grade-3 fibrosis occurred with 28Gy/4 fractions schedule. Additional details regarding toxicity were summarized in Table.

40Gy/1 0 fractio ns

35 Gy/7 fractio ns

28Gy/4 fractions

P- value

Total

N° patie nts Skin Acut e tox. Pain (acut e) Skin Late tox. Fibro sis Any acute tox. Grad e ≥2 Any late tox. Grad e ≥2

189

80

73

36

G2:4(5 %)

G2:2(2 .7%)

G2:6(3.2%)

0

G3:1(1 .3%)

G3:1(0.5%)

0

0

G2:2(1.1%)

0

0

G2:2(5.6%)

Pain (late) G2:2(1.1%)

0

0

G2:5(5.6%)

G2:4(11.1% )G3:3 (8.3%)

G2:5(6 .8%)

G2:13(6.9%)G3: 3(1.6%)

G2:4(5 %)

p=0. 22

4(5%) 2(2.7%) 0

p=0. 008

4(5%) 5(6.8%) 8(22%)

Conclusion The 3 proposed PBI schedules ensure good LC and DFS. Clinical outcomes and acute tolerance were similar among the three cohorts, but late toxicity was significantly higher in patients treated with 28Gy/4 fractions. For this reason the 28Gy/4 fractions schedule is not recommended. Clinical outcomes of 35Gy/7 fractions and 40Gy/10 fractions were comparable, but the 35Gy/7 fractions schedule is preferred because of its better convenience for the patients. PO-0952 Hypofractionated WBI in large-breasted patients: long-term toxicity of a prospective series F. De Rose 1 , A. Fogliata 1 , D. Franceschini 1 , C. Iftode 1 , G.R. D'Agostino 1 , T. Comito 1 , C. Franzese 1 , L. Di Brina 1 , E. Clerici 1 , M. Loi 1 , P. Navarria 1 , W. Gatzemeier 2 , A. Testori 2 , C. Tinterri 2 , F. Lobefalo 1 , S. Tomatis 1 , M. Scorsetti 1 1 Humanitas Research Hospital, Radiotherapy and Radiosurgery, Rozzano Milan, Italy ; 2 Humanitas Research Hospital, Breast Surgery, Rozzano Milan, Italy Purpose or Objective To evaluate the impact of breast size on long-term toxicity and cosmesis in breast cancer patients treated with hypofractionation and simultaneous integrated boost using volumetric modulated arc therapy (VMAT). Material and Methods Breast size was defined as the volume receiving at least 90% of the breast dose prescription (36.45 Gy). Two cohorts were identified: small-medium breasted patients (<1000 cc) and large-breasted patients (>1000 cc). All patients undergoing breast-conserving surgery were treated with hypofractionated VMAT to the whole breast (40.5 Gy in 15 fractions) and concomitant boost dose to the tumor bed (48 Gy in 15 fractions). Skin toxicity and cosmetic data were analysed as acute and late (at 2 and 5 years follow-up). Univariate binary logistic regression analysis was performed to evaluate the associations