ESTRO 2022 - Abstract Book

S1035

Abstract book

ESTRO 2022

PO-1225 Cardiac substructures in hypofractionated treatment schedules in left sided breast cancer

A. Ravi 1 , V. PAREEK 2 , M. BARTHWAL 2 , G. SHYAM 1 , A. A 1 , D. BORA 1 , V. GHOSH 1 , S. SANYAL 1 , S.K. SAMALA 1 , M.S. TANWAR 1 , S. MANDAL 1 , S. PANDEY 1 , D.V.S. PRAVEEN 1 , J. PATTANAIK 1 , S. NIRALA 1 , A.P. SOLANKI 1 , R. SISODIYA 1 , S. SHARMA 1 , D.N. SHARMA 1 , H. KP 1 , S. GUPTA 1

1 IRCH, AIIMS, RADIATION ONCOLOGY, NEW DELHI, India; 2 NCI, AIIMS, RADIATION ONCOLOGY, NEW DELHI, India

Purpose or Objective Hypofractionation radiation therapy in breast cancer are well- established treatment schedules. However, in left- sided breast cancer, the doses to heart and cardiac substructures are not well defined. In this study, we compare the radiation dose received by cardiac and the substructures in left-sided breast cancer. Materials and Methods Total 30 patients with histopathologically proven ductal carcinoma in left sided breast cancer, 15 each treated with 26Gy in 5 fractions (Group A) and 40Gy in 15 fractions (Group B) respectively. Planning Computerised Tomography (CT) was undertaken for each patient and organs at risk including the cardiac substructures, whole breast, heart, lungs, and contra lateral breast was contoured for each patient. Radiotherapy plans were made by standard tangent field. Mean and maximum heart dose, LAD, RCA, LCA and Left circumflex artery mean and V5 of right lung, and mean, V5, V10 and V20 of left lung, mean dose and V2 of contra lateral breast were calculated for each patient and compared using student’s T test. Results Mean doses to the heart were 16.4Gy and 8.45Gy respectively and left lung mean dose, V5, V10 and V20 were 5.91Gy, 14%, 12.8%, 11.7%; and 7.83Gy, 20.4%, 18.6% and 14.7% in group A and B, respectively. The dose to the distal LAD was significantly higher than proximal LAD both in both plans (p<0.001) signifying the need for contouring the distal LAD. Similarly, the doses were reduced in left circumflex artery with group with trending towards significance. There was no statistically significant difference in the doses to the other cardiac substructures in both groups. Mean dose to the right lung was significantly less in group A as compared to BCS, 0.31Gy vs. 0.64Gy, respectively (p = 0.027). Mean dose to the opposite breast was 0.52Gy and 0.37Gy respectively. Conclusion Our study emphasizes the need for contouring the cardiac substructures especially the distal LAD and Left circumflex artery. The hypofractionation schedule with 26Gy in 5 fractions has shown benefit in reducing doses to these cardiac substructures. There is a need for clinical studies to validate the results. J. Cantalino 1 , B. Collins 1 , M. Danner 1 , S. Rudra 1 , S. Suy 1 , S. Collins 1 , M. Pernia Marin 2 , M. Good 3 , D. Markiewicz 3 , R. Lanciano 3 , O. Obayomi-Davies 4 1 Medstar Georgetown University Hospital, Department of Radiation Medicine, Washington, DC, USA; 2 The George Washington University Hospital, Geriatric and Palliative Care Division, Washington, DC, USA; 3 Philadelphia Cyberknife, Crozer Keystone Health Care Center, Department of Radiation Oncology, Havertown, PA, USA; 4 Wellstar Medical Group, Department of Radiation Oncology, Marietta, GA, USA Purpose or Objective Outcomes following adjuvant accelerated partial breast irradiation (APBI) in select women with early-stage breast cancer are comparable to whole breast irradiation. Robotic stereotactic accelerated partial breast irradiation (RSAPBI) with fiducial tracking is an attractive treatment option, but limited data are available regarding the acute radiation toxicity of this approach. We report our mature acute radiation toxicity outcomes for a prospective multi-institutional trial treating select women with RSAPBI. Materials and Methods Post-menopausal women with DCIS and Stage IA breast cancer were treated over a five-year period extending from November 2015 to November 2020 and were followed for a minimum of one year. Treatments were delivered with a robotic radiosurgery system. Four gold fiducials were implanted around the lumpectomy cavity prior to the start of treatment for tumor bed delineation and target tracking. The CTV was defined as the lumpectomy cavity with a uniform 5-15 mm expansion confined to the breast tissue and the PTV was defined as the CTV with a 0-5 mm uniform expansion. The PTV was prescribed 30 Gy in 5 fractions. The maximum skin point dose allowed was < 36 Gy (skin = CT surface minus 2 mm). Breast examination was completed at 1 month, 3 months, and 6 months. At each follow-up a toxicity case report form was completed. Results Eighty-one patients (median age 68 years) with ER+/PR+ tumors were treated over a median 9 days (range, 5-15). Sixty- eight women had invasive ductal carcinoma (84%) and thirteen had DCIS (16%). The median treated PTV was 108 cm 3 (IQR 66-156) and the median prescription isodose line was 81% (IQR 79-83). The median CTV expansion was 10 mm (range 5-10) and the median PTV expansion was 3 mm (range 0-5). Acute grade 1 radiation dermatitis was seen in 12 of 78 evaluable patients at 1 or 3 months (15.4%). On multivariable logistic regression, PTV (OR 1.01, 95% CI 1.001-1.02, p=0.024) and skin dose > 32 Gy (OR 7.4, 95% CI 1.40-40.3, p=0.021) were found to be significantly associated with acute radiation dermatitis. No other acute radiation toxicities were observed. PO-1226 Stereotactic APBI for Early-Stage Breast Cancer: Acute Toxicity Outcomes of a Prospective Trial