ESTRO 36 Abstract Book

S641 ESTRO 36 _______________________________________________________________________________________________

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.

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- assisted breast cup and imaged on a CT simulator with 1 mm slice thickness. Once the cup is placed, the negative pressure is maintained until the treatment is delivered. An inversely optimized treatment plan is generated while the patient is transported and positioned in the treatment room. Typical time between the imaging session and completion of treatment is about 60 minutes. Results 5 of the first 6 enrolled patients completed the treatment. One patient’s lumpectomy cavity extended outside the immobilized portion of the breast and therefore did not meet the inclusion criteria for the study. With the sources near its half-life, the treatment time ranged from 17 minutes to 26 minutes. Dosimetrically, for the 5 patients who completed their treatment, more than 95% of the prescription dose covered the clinical target volume, and the maximum dose (D 2% ) varied from 13% to 20% of the prescription dose (see figure of sample dose distribution). With a median follow-up of 3 months, none of the patients developed treatment related toxicity. Conclusion Initial results indicate that the GammaPod system can deliver a focal dose of radiation to the breast safely. The vacuum-assisted breast cups were able to maintain the immobilization between imaging and treatment. With dynamic dose painting, the dose uniformity rivals that of external beam partial breast irradiation, but with more rapid dose fall-off outside the target, leading to substantially reduced radiation dose to the normal breast. The ability of delivering a focal dose of radiation opens the opportunity for single pre-operative irradiation as an alternative to intra-operative irradiation and pre- operative radioablation. EP-1184 HDR boost decreases the risk of breast failure in invasive breast ca. with close or involved margins J.L. Guinot 1 , M.I. Tortajada 1 , M.A. Santos 1 , F. Romero 1 , A. Moreno 2 , V. Campo 3 , L. Oliver 3 , P. Santamaria 1 , J. Fernandez 4 , L. Arribas 1 1 Fundación Instituto Valenciano de Oncologia, Department of Radiation Oncology, Valencia, Spain 2 Fundación Instituto Valenciano de Oncologia, Department of Radiation Oncology, Alcoy Alicante, Spain 3 Fundación Instituto Valenciano de Oncologia, Department of Radiation Physics, Valencia, Spain 4 Fundación Instituto Valenciano de Oncologia, Department of Radiation Oncology, Cuenca, Spain

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