ESTRO 2020 Abstract Book

S503 ESTRO 2020

patients. Toxicity was evaluated using CTCAE v.5.0 criteria. Several dosimetrical parameters were evaluated for critical organs at risk (OARs). Results Median follow-up was 15,7 months and median age was 65 years (48-81). Two patients were lost for the analysis and one was dead for non-tumor-related cause. Tumor and patients characteristics are shown in Table 1. During RT side-effects were: dermatitis G1-2 in 11(35%) patients, dermatitis G3 in 1(3%), fatigue G1-2 in 9(29%) and no more grade 3 side-effects. Among the 19 patients with at least 6 months of follow-up after RT, 16(84%) patients were asymptomatic and hyperpigmentation appeared in 3(16%). At 1 year follow-up, hyperpigmentation appeared in 3(27%) of 11 patients. All patients are alive without any sign of disease. Regarding OARs, all dosimetrical parameters were within tolerance limits. Complete dosimetrical details are shown in Table 2.

20 patients with similar volume delimitation and 3D dosimetry treated using DIBH to a control group of FB. Dose volume were analyzed for V5, V20, V25, Dmean to the heart and left lung on FB and DIBH scans. We measured CCD in CCDax and CCDps planes, on FB and DIBH scans.

Results Dose to heart and left lung was significantly lower in DIBH plans than in FB by all metrics. When DIBH was compared with FB, Dmean for heart was 0.91 vs 2.37 Gy (p<0,001). Overall, DIBH reduced Dmean to the cardiac structures by 46,56% compared with FB. Equally significant were differences in V5, V20, V25 for all cardiac and Lung structures. When was compared percent Dmean reduction between CCD in both the CCDax and CCDps planes on FB and DIBH, using the Spearman’s rank coefficient, there was no correlation between those variables (p>0,05) in both cases.

Conclusion Patients treated with DIBH we have found that, compared to FB patients, there is a large reduction in heart and lung doses. The technique is simple, well tolerated by patients and can be implemented for routine in radiation therapy of left sided breast cancer. PO-0942 Post-mastectomy radiotherapy after Immediate versus Two-Stage Breast Reconstruction. E. Bonzano 1 , M. Guenzi 2 , B. De La Lande 3 , E. Musat 3 , H. Albert-Dufrois 3 , J. Otz 3 , A. Clément-Zhao 3 , A.R. Filippi 4 , R. Corvò 2 , P. Poortmans 5 1 Fondazione IRCCS Policlinico San Matteo and PhD school in Experimental Medicine University of Pavia, Department of Radiation Oncology, Pavia, Italy ; 2 IRCCS Policlinico San Martino and University, Department of Radiation Oncology, Genova, Italy ; 3 Institut Curie Rene Huguenin Hospital, Radiotherapy Department, Saint Cloud, France ; 4 Fondazione IRCCS Policlinico San Matteo, Department of Radiation Oncology, Pavia, Italy ;

Conclusion According to our data, VMAT is a safe, effective and tolerable technique for the RT treatment of SBBC patients. Longer follow-up is needed to asses chronic toxicity. PO-0941 Deep inspiration breath-hold technique for the treatment of breast cancer: reduction of cardiac dose L. Montezuma 1 1 Hospital del Mar, Radiotherapy, Barcelona, Spain Purpose or Objective The purpose of this study was to evaluate the efficacy of voluntary deep inspiration breath-hold (DIBH) over the free breathing (FB) radiation therapy technique by comparing percent mean cardiac dose (Dmean) reduction. Also the correlation between cardiac contact distance (CCD) in both the axial (CCDax), parasagittal (CCDps) planes and Dmean was assessed. Material and Methods