ESTRO 36 Abstract Book

S635 ESTRO 36 2017 _______________________________________________________________________________________________

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. Results : 12 patients had mastectomy and 1 patient had lumpectomy. 7 patients had immediate reconstruction: 2 tissue expanders, 5 autologous deep inferior epigastric perforator flaps. All patients received systemic chemotherapy. Toxicity was evaluated once weekly. 84 % (11/13) of patients had G1 skin toxicity, while 15 % had G2-G3 (2/13) toxicity. In one patient with G3 toxicity skin dose was intentionally increased with a bolus. 1 patient had G1 esophagitis and there was no acute lung toxicity. CTV coverage was within limitations for all patients (V 93% PD > 99%). For evaluation PTV (target volume reduced by 5mm buildup region) the selected target dosimetric metrics were the following: for left-sided breast treatment V 95% PD = 96.8% (standard deviation – SD 3.7%), V 107% PD = 3.7% (SD 5.4%) and for right-sided breast treatment V 95% = 96.3% (SD 4.7%), V 107% PD = 1.0% (SD 0.7%). Dosimetric metrics for OARs for the whole group were: heart D mean = 5.6 Gy (SD 3.2 Gy), V 20 Gy = 4.9% (SD 6.4%), for both lungs D mean = 9.6 Gy (SD 1.7 Gy), V 20 Gy = 15.9% (SD 3.4%), for contralateral lung V 5 Gy = 8.7% (SD 16.8%) and for contralateral breast D mean = 1.7 Gy (SD 1.0 Gy). Dose to the OARs and restrictions are presented separately for left and right side in table 1.

Conclusion Conclusion : IMRT of breast/chest wall and regional lymph nodes in patients with challenging anatomy is feasible with acceptable short term toxicity. We had some difficulties in balancing constraints for OARs and target coverage especially in left-sided breast treatment. Better results may be achieved with the introduction of deep inspiratory breath hold (DIBH) combined with IMRT or even VMAT technique. EP-1183 Initial Clinical Experience with a Noninvasive Breast Stereotactic Radiotherapy Device: the GammaPod S. Feigenberg 1 , E. Nichols 1 , Y. Mutaf 1 , W. Regine 1 , S. Becker 1 , Y. Niu 2 , C. Yu 1 1 University of Maryland School of Medicine, Radiation Oncology, Baltimore, USA 2 Xcision Medical Systems, Research, Columbia- MD, USA Purpose or Objective GammaPod TM is a new stereotactic radiotherapy device dedicated to the treatment of breast cancer. It creates a radiation focal spot with sharp dose fall-off at the isocenter by using 36 non-overlapping rotating cobalt-60 beams, and creates a uniform dose coverage by dynamically moving the focal spot within the breast in the prone position. A US FDA approved clinical study is being conducted at the University of Maryland. Herein reported is the initial experience with this novel device. Material and Methods The purpose of this clinical study is to evaluate the feasibility and safety of using the GammaPod TM system to deliver a focal dose of radiation to a target in the breast. Of the 17 planned enrollments, 6 patients have been completed and we expect to complete this trial by the end of 2016. A single ‘boost’ dose of 8 Gy is delivered post-operatively to the tumor bed plus a 10mm margin using the GammaPod TM , followed by whole breast irradiation with either hypofractionation of 15 fractions or a conventional fractionation scheme of 25 fractions. Eligibility criteria include minimum age of 60, with Stages I or II breast cancer, lumpectomy volume less than 30% of the whole breast volume, and the lumpectomy within the immobilized breast. Prior to treatment, the affected breast is immobilized with a patented vacuum-