ESTRO 2020 Abstract Book

S793 ESTRO 2020

prescribed dose for WBI was 39.9 Gy in 15 fractions. For each patient in TPS Monaco v.5.1 (Elekta) 3 plans were generated: 3D-CRT, IMRT and VMAT. The following parameters were compared separately for left and right breast: PTV coverage by the 95% isodose (PTV 95% ), mean heart and lung) doses (D mean H, D mean L), percentage volume of ipsilateral and contralateral lung receiving doses: 5 Gy (V 5Gy ipsL, V 5Gy contrL), 20 Gy (V 20Gy ipsL, V 20Gy contrL). Also percentage volume receiving 5Gy for contralateral breast (V 5Gy contrB) and whole body volume receiving 5 Gy (V 5Gy Body) were compared. Maximum dose for left anterior descending coronary artery (D max LAD) and mean dose for left ventricle (D mean LVentr) were compared for left-sided only. The Wilcoxon signed rank test was used to compare 3D-CRT, IMRT, VMAT plans differences, while the data were analyzed by STATISTICA v.13.1software (Statsoft, Poland). The results were considered statistically significant at a p-value less than 0.05. Results The results are presented in Table 1. There was no difference in the PTV coverage for compared techniques. For left breast: IMRT and VMAT decreased significantly D max LAD compared to 3D-CRT; VMAT , but not IMRT was beneficial over 3D-CRT for D mean LVentr; mean heart dose was not different for all of compared techniques.For right breast: there was no significant clinical improvement for OAR seen. Additionally, IMRT and VMAT increased mean heart dose, however in the range of very low doses. For both sides, V 5Gy ipsL, V 5Gy contrB, and V 5Gy Body increased significantly for IMRT and more for VMAT than for 3DCRT.

Gamma (1% / 1 mm) 100 million photons

Gamma (1% / 1 mm) 4 million photons

Protocol Name

CBCT 5s DR Body Care CBCT 12s DCT Large Volume L CBCT 12s DCT Large Volume P CBCT 6s DCT Body CBCT 20s DCT Head 70kV CTCT 20s DCT Head 109kV CBCT 10s DCT Head

84.5%

84.7%

68.2%

72.7%

94.3%

96.4%

95.0%

96.1%

94.9%

97.9%

98.2%

99.1%

98.9%

99.3%

PCT 150 mAs 99.2% PCT 250 mAs 99.2%

99.5% 99.5%

Table

1

Figure 1: Variances and calculation time in dependency of number of photons used for MC simulations. Conclusion Conventional intraoperative CBCT scanning is suitable for Monte Carlo based online 3D kV treatment planning, paving way for image-guided intraoperative radiotherapy. However, trade-offs between simulation times and variance of doses need to be considered. PO-1477 Comparison of 3D-CRT, IMRT and VMAT plans (including low body dose) for whole breast irradiation B. Czeremszynska 1 , A. Rygielska 2 , A. Walewska 2 , M. Gabor 2 , D. Pruska-Pich 2 , K. Osowiecka 3 , L. Kepka 1 1 Military Institute od Medicine, Radiotherapy Department, Warsaw, Poland ; 2 Military Institute od Medicine, Radiotherapy Department- Laboratory of Medical Physics, Warsaw, Poland ; 3 University of Warmia and Mazury, Department of Public Health, Olsztyn, Poland Purpose or Objective It is believed that dynamic radiotherapy techniques may improve the therapeutic ratio of radiotherapy for breast cancer. We compared the PTV coverage and doses in organs at risk (OAR) for 3D-CRT, IMRT and VMAT plans in whole breast irradiation (WBI). Material and Methods 22 (15 left breasts, 7 right breasts) consecutive patients addressed for WBI without lymph node irradiation were included. Patients were treated with free breathing; total

Conclusion All 3 compared techniques provided adequate PTV coverage. The dose reduction for LAD and left ventricle in left WBI with dynamic techniques was obtained at the price of higher body integral dose related to higher volume of low dose given to OAR. Such a reduction may be