Abstract Book

S699

ESTRO 37

local recurrence rate. Secondary endpoints included the overall survival rate, toxicity and cosmetic outcome. Toxicities were documented using the Common Terminology Criteria for Adverse Events v3.0 (CTCAE) and Cosmesis was evaluated after 6 months using Harvard/NSABP/RTOG Breast Cosmesis Grading Scale. Results At a median follow-up of 43 months, ipsilateral local recurrence was observed in one of eighty-one patients (1.2%) which occurred in the same quadrant of the breast index. 3-year overall survival rate was 89.8%. Treatment was well-tolerated with no grade 3-4 acute and late toxicity. 87% of patients were recorded Excellent-good cosmesis. Conclusion Breast-conserving surgery with IORT as a boost resulted in low local recurrence rate and excellent cosmetic outcome. IORT as a boost could be considered as an alternative to external beam boost. Prospective studies are needed to confirm this data. EP-1267 Dosimetric comparison of prone vs supine partial breast irradiation via EBRT in early breast cancer A. Thimmarayappa 1 , U. A S 1 , L. Vishwanath 1 , V. C 2 , N. Thimmaiah 1 , B. Joseph 1 , K.P. Jagannath 1 , T. Pasha 1 , V. Ramaiah 1 , G. H B 1 , S. S D 1 1 kidwai Memorial Institute Of Oncology, Radiotherapy, Bangalore, India 2 kidwai Memorial Institute Of Oncology, Medical Physics, Bangalore, India Purpose or Objective To analyzed the dosimetry of PTV and OARs - heart and lungs in prone versus supine hypofractionated partial breast irradiation. Material and Methods Twenty histologically proven, newly diagnosed early stage carcinoma breast with informed consent were enrolled for the study. All patient underwent breast conservation surgery followed by Adjuvant RT. A CTV of 1.5cm was generated from the cavity followed by 0.5 mm PTV margins. 3DCRT or IMRT plans were generated in both the positions. Patient was treated in supine position to a dose of 40Gy delivered in 15 fr at 2.66Gy per faction, 1 faction per day over 5 fractions per week. Dose constraints were applied to the OARs namely then ipsilateral lung V 30 <10%, V 20 <20%, V 30 <10% and the heart V 20 <5%, V 10 <10% and D mean <5Gy. In our study the PTV Dosimetric parameters were assessed using PTV D 90 , PTV V 95 and PTV D max . Lung Dosimetric parameters were mean ipsilateral lung V 30 , V 20 and V 10 and Heart Dosimetric parameters were V 20 , V 10 and mean heart dose. Results Between October 2014 and December 2016, 20 patients were enrolled on the study. The PTV D 90 was 37.91Gy in supine position and 38.03Gy in prone position. The PTV D max was 106.22Gy in supine position and 105.87Gy in prone position. The PTV V 95 was 91.73% in supine and 93.77% in prone position. The mean ipsilateral lung V 30 was 6.69% in supine and 2.45% in prone position which was statistically significant (p =0.002). The mean ipsilateral lung V 20 was 11.05% in supine and 4.87% in prone position which was statistically significant (p = < 0.001). The mean ipsilateral lung V10 was 17.82% in supine and 7.97% in prone position which was statistically significant (p = < 0.001). The mean ipsilateral lung dose was 6.37Gy in supine position and 3.10Gy in prone position which was statistically significant (p = <0.001). The Heart V 20 was 1.28% in supine position and 1.53% in prone position. The Heart V 10 was 3.99% in supine position and 3.19% in prone position. The mean heart dose was

1.86Gy in supine position and 1.48Gy in prone position. None of the parameters were statistically significant. Lung dosimetric parameter Supine Prone p value

6.69+/- 6.15 11.05+/- 6.82 17.82+/- 8.21 6.37+/- 2.58

2.45+/- 2.02 4.87+/- 3.03 7.97+/- 4.34 3.10+/- 1.75

Ipsilateral lung V30

0.002

Ipsilateral lung V20

<0.001

Ipsilateral lung V10

<0.001

Ipsilateral lung mean dose (Gy)

<0.001

Conclusion Prone position in breast irradiation provided a better dosimetry for ipsilateral lung. Although the cardiac dose was reduced by prone position compared to supine position, DVH parameters V 20 , V 10 and mean heart dose, were not statistically significant.The DVH parameter for the PTV in prone position were not found to be statistically significant compared to supine position. EP-1268 Breast cancer irradiation using proton pencil beam scanning A. Pasztorova 1 , J. Kubes 1 , M. Andrlik 1 , B. Ondrova 1 , G. Kasacova 1 , K. Dedeckova 1 , S. Slavikova 1 , P. Vitek 1 , S. Vinakurau 1 , J. Kvech 1 , V. Vondracek 1 , M. Navratil 1 1 PROTON THERAPY CENTER CZECH, Proton Therapy Department, Prague 8, Czech Republic Purpose or Objective Proton therapy using pencil beam scanning (PBS) in breast cancer irradiation allows for the achievement of perfect coverage of the target volumes while maximising the sparing of the heart, contralateral breast and lungs. It is necessary, as for other dynamic irradiation techniques, to suppress the influence of the breathing interplay effect on the final dose distribution. Moreover, proton therapy using PBS brings other requirements for the patient setup precision. Material and Methods The breast cancer of forty-two patients was treated by PBS from April 2015 to September 2017. The patients were irradiated in deep-breath hold using Dyn´R spirometer. The average age was 55 years (min 25 years, max 75 years). The stage was from pTis to pT3 (2x pTis, 5x pT1b, 21xpT1c, 12x pT2 and 2x pT3). There were 39 patients with a left-side tumour and 3 patients with a right-side tumour. From this group, 11 patients were treated with locoregional irradiation (nodes included) and 31 patients were treated for breast only. The selected fractionation was the standard ( 25x2)+ boost (7-8x2) for 29 patients, accelerated (16x2.67) + boost (4x2.5) for 11 patients, (16x2.67) with no boost for 1 patient, 30x2 for 1 patient and a Simultaneously Integrated Boost (28x1.85+28x2.25) for 1 patient. We evaluated acute and late toxicity, dosimetric parameters of the ipsilateral lung, contralateral lung, heart (right and left atrium, right and left ventricle), right and left coronal arteria (incl. LAD, r. circumflexus) and the contralateral breast. Results All patients finished radiotherapy without interruption. Median observation was 7 months. The dosimetry parameters are published in following table. Acute toxicity was evaluated by RTOG criteria. The acute toxicity G1 was reported in 23 patients (55%), G2 in 18 patients (43%), G3 in 1 patient (2%). Late toxicity was reported in 12 patients (54%), G1 in 7 patients (32%), G2 in 3 patients (14%). No relapse was observed .