ESTRO 36 Abstract Book

S990 ESTRO 36 2017 _______________________________________________________________________________________________

Denmark after the data from the DBCG-IMN study was released in 2014 [1]. In that study it was shown that in general patients benefit more from having IMN included in the fields compared to the risk of ischemic heart disease. We wanted to evaluate the clinical relevant changes caused by this new practice in our clinic. Material and Methods The dose plans for 45 consecutive patients (20 patients before and 25 after the new practice, respectively) were retrospectively evaluated with respect to V5Gy, V20Gy, V40Gy and mean dose for the heart (MHD), V20Gy and mean dose (MLD) for the ipsilateral lung and V45Gy (prescription dose) for IMN. According to national guidelines the following constraints should be aimed at: V20Gy ≤ 10% and V40Gy ≤ 5% for the heart, V20Gy ≤ 35% for the ipsilateral lung and MLD ≤ 18 Gy. After the change according to local guidelines V20Gy should not exceed 40% for the ipsilateral lung. Results Changing the clinical practice trying to increase V45Gy to IMN has resulted in higher median dose to the heart for all parameters investigated – see Table 1. Median MHD increased from 1.50 Gy to 1.85 Gy corresponding to 16.4% and 20.1% increase in rate of major coronary event, respectively [2]. The V20Gy and V40Gy constraints for the heart was violated in one and two cases compared to four and three before and after, respectively. V20Gy for the ipsilateral lung was larger than 35% for one patient before compared to seven patients after the change. V20Gy never exceeded 40% for any patient. MLD was larger than 18 Gy for one patient before and in no cases after. The median volume of IMN receiving the prescription dose (45 Gy) of higher increased from 74.7% to 87.8%. Conclusion Paying more focus to increasing V45Gy for IMN resulted in better target coverage at the expense of higher doses to heart and ipsilateral lung. However the increased dose to heart and lung is believed to be justified by better survival due to better target coverage of IMN . [1] CT-planned internal mammary node radiotherapy in the DBCG-IMN study - benefit versus potentially harmful effects, Thorsen et al , Acta Oncologica, 2014; 53: 1027- 1034 [2] Risk of Ischemic Heart Disease in Women after Radiotherapy for Breast Cancer, Darby et al , N Engl J Med 368:11 987-998 EP-1835 Independent verification of treatment planning system calculations E. Dąbrowska 1,2 , B. Brzozowska 1 , A. Walewska 2 , P. Kukolowicz 2 , A. Zawadzka 2 1 Faculty of Physics University of Warsaw, Department of Biomedical Physics, Warsaw, Poland 2 Maria Sklodowska-Curie Memorial Cancer Center and Institute of Oncology, Department of Medical Physics, Warsaw, Poland Purpose or Objective In accordance to the EURATOM directive 97/43 (EURATOM, 1997) there must be an independent dose verification procedure for quality assurance in all clinical radiotherapy routines. Referring to Report of AAPM Task Group 114, this procedure can be performed e.g. by second treatment planning system (TPS). The aim of this study was to compare and quantify the differences in dose distribution obtained with two commercially available radiotherapy TPS: the Eclipse (Varian) and the Oncentra MasterPlan (Nucletron).

EP-1834 Dose to internal mammary nodes compared to dose to heart and lung for breast cancer patients M. Berg 1 , M. Christensen 2 , M. Andersen 2 , N. Kiilerich 2 1 Vejle Hospital, Department of Medical Physics, Vejle, Denmark 2 University College Lillebaelt, Department of Radiology and Radiotherapy, Odense, Denmark Purpose or Objective Prioritization of internal mammary nodes (IMN) over dose to the heart and ipsilateral lung for patients having left- sided radiotherapy (RT) to the residual breast and regional lymph nodes left-sided breast cancer has changed in