ESTRO 2020 Abstract Book

S508 ESTRO 2020

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.

Conclusion The results of this study showed that chest-wall irradiation is associated with subclinical cardiac impairment, especially in the first six months after radiotherapy. However, further follow-up is necessary the determine the definitive impact of observed changes. Based on the observed changes in the parameters of right heart, it can be concluded that these parameters are negatively correlated with the dose of the heart. Concerning left cardiac parameters, it is marked that the major effect of radiotherapy is on the diastolic function of the left heart, 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

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%)

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

G2:4(5 %)

G2:5(6 .8%)

p=0. 22

4(5%) 2(2.7%) 0

p=0. 008

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

Conclusion