ESTRO 36 Abstract Book

S640 ESTRO 36 _______________________________________________________________________________________________

Material and Methods From 2006 to 2010, 832 patients with early-stated breast cancer treated by conservative surgery underwent 3D- conformal whole breast RT in the lateral decubitus position at Institut Curie. All types of cup size was included. The acute toxicity of treatement was evaluated weekly using NCI CTC v3.0 scale, and the late toxicity was evaluated once a year and started one year after the end of RT. A dosimetric study was performed to analyse the mean cardiac dose and the mean homolateral and controlateral lung doses. Results median of follow up is 6.4 years, median age is 61,5 years (min29-max90), and median body mass index is 26.3. 51% have left breast cancer and 49% have right breast cancer. Different type of fraction/dose were performed : 46.5% 66Gy in 33 fractions, 17.9% 50Gy in 25 fractions, 26.1% 40 or 41.6Gy in 15 or 13 fractions and 30Gy in 5 fractions. Acute epidermitis was present in 93% with a median of apparition of 4 weeks, and only 2,8% grade 3. In multivariate analysis, the cup size has signicative influence (p=0,0004) and the fractionation has a significative influence (p=0,0001). After one year 94.1% had no epidermitis. No cardiac or pulmonary toxicity was reported. For normofractionation (2Gy fractions, 50 Gy on the whole breast and 16Gy boost on the tumor bed) : Mean dose to homolatéral lung (HL) is 1,4 Gy (min 0,63 Gy-max 3 Gy), mean dose to controlateral lung (CL) is 0,07Gy (min0,37Gy-max1Gy) mean cardiac dose is 1,14 Gy (min0,54 Gy – max4 Gy). In hypofractionation : for 41,6Gy in 13 fractions schedule : mean dose to HL is 0,87Gy (min0,38 Gy-max5 Gy), mean dose to CL is 0,03 Gy (min0,3 Gy-max3 Gy) mean cardiac dose is 0,77 Gy (min0,38 Gy- max9 Gy). For 40 Gy en 15 fractions schedule : mean dose to HL is 0,96 Gy (min0,38 Gy-max4 Gy), mean dose to CL is 0,04 Gy (min0,02 Gy-max2,28 Gy) mean cardiac dose is 0,74Gy (min0,3 Gy-max1 Gy). In the 28,5Gy en 5 fractions schedule : Mean dose to HL is 0,53Gy (min0,26Gy- max3Gy), mean dose to CL is 0Gy (min0 Gy-max0,4 Gy) mean cardiac dose is 0,37Gy (min0,6 Gy-max5 Gy). Median overall survival is not reached, there is no influence of fractionation on overall survival. Relapse-free survival is not reached, with only 36 relapses without influence of fractionation. Conclusion whole breast radiotherapy in the lateral decubitus position provides excellent results with very low mean cardiac dose and mean pulmonary dose. There is no cardiac or pulmonary toxicity in this study. And it’s also very well tolerated with very good acute toxicity profile. EP-1181 dose to non-routinely delineated risk organs in post left conservative surgery conformal breast RT M. Abdelwahed 1 , M.A.H. Mohamed Abdelrahman Hassan 2 1 As-Salam International Hospital, oncology, Cairo, Egypt 2 Kasr Alaini Center of Clinical Oncology & Nuclear Medicine NEMROCK, clinicla oncology, cairo, Egypt Purpose or Objective This is a dosimetric study aiming at evaluation of radiation doses to risk organs particularly (brachial plexus, coronary artery & thyroid gland) in previously treated breast cancer cases at Kasr Alaini Center of Clinical Oncology & Nuclear Medicine after left Breast Conservative Surgery (BCS) Our aim was to identify the patients' subgroups in need for routine delineation of these risk organs to avoid toxic doses to them. Material and Methods Twenty five female patients with left BCS treated with external beam radiotherapy to the left breast and supraclavicular region. Delineation of the coronaries was done according to the University of Michigan Medical Center; while the brachial plexus was delineated

according to the RTOG guidelines. Patient measures like body mass index (BMI), mid beam cut separation, Central lung distance, Maximum heart distance (MHD) and doses to risk organs were documented (Heart V 30 & heart D mean , brachial plexus D max , thyroid gland D mean ,…) Results Age of the patients ranged from 35years to 70 years (median=54years). BMI ranged from 22.1 to 47.6 (mean=34.2±6.7). MHD mean value was 2.9±1.1cm while the heart V 30 mean value was 3.44±3.59% with heart D mean range from 1.2 up to 9.00Gy (mean=3.92±2.02Gy). The anterior descending coronary artery (ADCA) D max was 41.9±6.60Gy while the ADCA D mean was 23.4±10.9Gy. ADCA D mean increased from 18.5±10.9Gy with MHD ≤3cm to 27.9±9.1Gy with MHD >3cm (ρ-value 0.030). ADCA D mean was also related to V 30 of the heart as the ADCA Dmean was 16.9±10.5Gy with V 30 <2% while ADCA D mean was 29.5±7.3Gy with V 30 ≥2% (ρ-value=0.005). BMI showed borderline significance on ADCA D max when the BMI was <30, the ADCA D max was 37.3±10.0Gy while it was 43.7±43.7Gy when BMI ≥30 with a ρ-value 0.074. None of the outcome parameters had clinical significance related to the thyroid gland or brachial plexus, The brachial plexus D max was 46.7±3.0Gy with median value 46.0Gy while the thyroid gland D mean was 20.6±5.3Gy with median value 20.0Gy. Conclusion A significant dose may be received to non-routinely delineated organs at risk (brachial plexus, coronary artery & thyroid gland) in post-operative loco-regional radiotherapy of patients with left breast cancer after BCS. A significantly higher dose was received to left ADCA in cases with high MHD & heart V 30 while borderline significance on ADCA in obese patients where obesity is a known risk factor for developing coronary artery diseases. EP-1182 Locoregional treatment of breast cancer with IMRT: a single center experience I. Ratosa 1 , A. Jenko 2 , R. Hudej 2 , F. Kos 2 , A. Gojkovic Horvat 1 , D. Golo 1 , T. Marinko 1 , M.S. Paulin Kosir 1 , J. Gugic 1 1 Institute of Oncology Ljubljana, Department of Radiation Oncology, Ljubljana, Slovenia 2 Institute of Oncology Ljubljana, Department of Radiation Oncology- Section of Medical Physics, Ljubljana, Slovenia Purpose or Objective To evaluate implementation of breast/chest wall and locoregional lymph nodes irradiation with inverse-planned IMRT in patients with challenging anatomy. Material and Methods Since 2014, 13 patients with challenging anatomy (8 left-, 5 right-sided) were treated with locoregional IMRT on institutional protocol because standard mono-isocentric 3D-CRT was insufficient in sparing organs at risk (OARs). Dose prescription to planning target volume (PTV) was 50 Gy in 25 daily fractions; 3 patients were also prescribed boost dose 10−16 Gy. Treatment planning was done on Elekta Monaco TPS with Monte Carlo calculation algorithm. In the IMRT plan 9 beams with the energy of 6 MV were positioned so that the first two beams were placed tangentially on the PTV (as in a 3D-CRT plan) and the rest were redistributed equidistantly between the tangential pair. The cranial part of beams that would pass through the shoulder into the PTV was blocked with jaws. Two segmetation methods were used, Step-and-Shoot for the first 7 patients and Dynamic MLC (dMLC) for the rest. The primary endpoint in treatment planning was CTV coverage. Radiation was delivered on Elekta Synergy™ Platform linac for Step-and-Shoot mode and Elekta Versa HD™ for dMLC mode.