ESTRO 36 Abstract Book

S446 ESTRO 36 2017 _______________________________________________________________________________________________

Left breast results: Identical coverage was achieved with a D95 of 95.2% ±0.4 (DIBH) vs. D95= 95.4%±0.6 (FB)(p=0.27). No statistical difference were found in D98, median and D2 (Figure1.A). Left lung results: No statistical difference was also found (Figure1.B). Heart results: Doses were significantly lower with DIBH; Dmean at 1.5Gy±0.8 (DIBH) vs. 2.9Gy±1.6 (FB) (p<0.001) and Dmax at 36.3Gy±14.7 (DIBH) vs. 46.2Gy±6.6 (FB) (p=0.004). DVH metrics for V10, V20, V30, and V40 were all significantly better in DIBH (Figure1.C). LAD coronary results: Doses were significantly lower with DIBH with Dmean at 9.5Gy ± 7.2 (DIBH) vs. 21.8Gy±11.4 (FB) (p<0.001) and a Dmax at 29.2Gy±17 (DIBH) vs. 42.3Gy±12 (FB) (p=0.003). DVH metrics favored the DIBH plans significantly all across the range of doses (Figure.1D). Conclusion In the treatment left breast cancer, 3D-DIBH showed superior dosimetric advantages in comparison to 3D-FB. Both heart and LAD were significantly spared without compromising left breast coverage. The LAD was spared for doses ranging from the low dose spectrum to the highest dose. PO-0837 Dosimetric advantages afforded by Dynamic WaveArc therapy accelerated partial breast irradiation Y. Ono 1 , M. Yoshimura 1 , K. Hirata 1 , N. Mukumoto 1 , T. Ono 1 , M. Inoue 1 , M. Ogura 1 , T. Mizowaki 1 , M. Hiraoka 2 1 Kyoto University- Graduate School of Medicine, Department of Radiation Oncology and Image-applied Therapy, Kyoto, Japan 2 Japanese Red Cross Wakayama Medical Center, Department of Radiation Oncology, Wakayama, Japan Purpose or Objective We identify dosimetric advantages of the novel volumetric modulated arc therapy (VMAT) featuring continuously varying non-coplanar trajectories. This is the Dynamic WaveArc (DWA) therapy used for accelerated partial breast irradiation (APBI). The dose distribution of DWA therapy was compared to that of non-coplanar three- dimensional conformal radiotherapy (3D-CRT) and coplanar VMAT. Material and Methods We evaluated APBI dose distributions, delivered via DWA, in 24 left-side breast cancer patients via non-coplanar 3D- CRT from November 2011 to April 2016 at our institution. The prescribed dose was 38.5 Gy in 10 fractions. The Vero4DRT enables DWA by continuous gantry rotation and O-ring skewing with moving dynamic multi-leaf collimator (MLC). Thus, the Vero4DRT delivers non-coplanar VMAT without couch rotation, minimizing dose delivery to adjacent organs at risk (OARs). We created two sets of 11 control points (at angles 315-35° to the O-ring angle, and 110-155° and 290-355° to the gantry angle), for two non- coplanar DWA trajectories. DWA, non-coplanar 3D-CRT, and coplanar VMAT treatment plans were created by a clinical treatment planning system, Raystation, using a collapsed cone dose-calculation algorithm (Figure 1-A). The mean DWA doses to the planning target volume (PTV), the bilateral breasts, the lungs, the heart, the left

Conclusion Even though the analyzed IGRT protocol focuses entirely on the gold seed of the prostate the needed margins for the lymph nodes are only slightly larger than 5 mm which in many centers are used as a standard PTV margin. Thus, the additional margin needed to include the lymph nodes is actually somewhat modest. However, the optimal balance between dose coverage of tumor and lymph nodes both in regard to local control and toxicity is still unclear, and needs further investigation. PO-0836 Impact of Deep Inspiration Breath Hold on Left Anterior Coronary dose in Left Breast irradiation. F. Azoury 1 , S. Achkar 1 , N. Farah 1 , D. Nasr 1 , C. El Khoury 1 , N. Khater 1 , J. Barouky 1 , R. Sayah 1 , E. Nasr 1 1 Hotel Dieu de France Hospital - Saint Joseph University, Radiation Oncology, Beirut, Lebanon Purpose or Objective Irradiation of Left breast cancer exposes women to higher doses to the heart and LAD coronary. Blocking the heart in the tangent fields will inevitably cause under dosage in proximity to the tumor bed. Here we evaluate the effect of deep inspiration breath hold (DIBH) on the coverage of the whole breast and the reduction of heart and LAD doses. Material and Methods We performed a dosimetric study on 25 patients treated with DIBH for left breast cancer utilizing RPM (Varian Medical Systems). Treatment plans were generated in Free Breathing (FB) and DIBH. Optimization was done with 3D Field-in-Field technique utilizing two-tangent setup. Care was taken to cover the whole breast volume. Prescription dose was 50Gy in 25 fractions. Planning objectives were: near minimum dose (D98) > 90% (45Gy), near maximum dose (D2) <105% and a median dose of 50Gy. Doses to the heart, LAD and left lung were compiled, left breast coverage was evaluated, and statistical analysis was performed using Student T-test with a 95% Interval of confidence. Results