ESTRO 38 Abstract book

S714 ESTRO 38

instead of 3B, further decreased the MLD (p=0.001) and had a positive impact on the V2 CLB (p=0.009)(table 1). No added value in reducing the dose to the OARs has been observed by using NCB (2B vs 2NCB, 3B vs 3NCB and 4B vs 4NCB), except for the MLD when comparing 3B with 3NCB. The difference in OAR doses with increasing the number of beams or by using NCB did not translate in a delta NTCP of ≥ 2%.

year after RT. Only one G2 fibrosis/teleangiectasia was observed, but maintaining a good cosmetic result. Four pts were dead at the last follow up: one of head and neck tumor, one of stroke and two of heart attack. The treatment plans of the two pts died of heart attack (one left sided tumor) were revised, but heart dosimetry was very good in both: V95%= 0 cc for both, V 20 Gy 0 for right sided, 0.76 cc for left sided pts and D 5 1.5 Gy for the right sided and 2.03 Gy for left sided patients, respectively. Two pts (1.52%) presented local relapse (4.4 and 7.9 years after HRT), 1 patient lymph-nodal relapse and 4 pts (3.02%) distant relapse. Conclusion Elderly pts with LRBC treated with adjuvant RT showed a good treatment tolerance and low local relapse (LR) rate, lower than the up to 9% reported without RT. Thus, a short, convenient HRT could be prescribed even in the absence of a survival benefit, due to the improvement of the quality of life by the reduction of the LR rate to a very low level. EP-1304 What is the benefit of using more beams and/or non-coplanar beams in breast PBS proton therapy? K. Verhoeven 1 , R. Houben 1 , K. Limpens 1 , M. Velders 1 , F. Visser 1 , G. Vilches-Freixas 1 , C. Ares 1 , G. Bosmans 1 , L. Boersma 1 1 GROW School for Oncology and Developmental Biology- Maastricht University Medical Centre, Radiation- Oncology Maastro Clinic and ZON-PTC, Maastricht, The Netherlands Purpose or Objective Pencil Beam Scanning (PBS) proton therapy (PT) has dosimetric advantages over photon therapy (PhT) in decreasing the dose to the organs at risk (OAR), which potentially leads to a reduction in late toxicity. To reimburse PT in breast cancer (BC) patients in our country a delta normal tissue complication probability (NTCP) of ≥ 2% for cardiac toxicity should be demonstrated based on the delta mean heart dose (MHD)[Darby et al, 2013] coming from the planning comparison between the PhT plan and the PBS PT plan. The use of more beams (B) and/or of non-coplanar beams (NCB) will increase the treatment delivery time. Therefore, the aim of this study is to investigate the dosimetric added value of increasing the number of beams as well as the use of NCB in PBS PT for BC patients. Material and Methods Fifteen BC patients (6 right and 9 left-sided) were selected for this dosimetric study. In 9/15 patients the internal mammary lymph node region was included in the target volume and 9/15 patients had an indication for a simultaneous integrated boost (SIB) on the tumorbed or on a macroscopic lymph node. The fractionation schemes used were 15 x 2,67Gy (1/15), 16 x 2.66Gy (5/15) and for SIB: 20 x 2,67Gy (1/15), 21 x 2,66Gy (3/15) or 23 x 2.66Gy (5/15). Six PBS PT plans were calculated for each patient: 2B, 2NCB, 3B, 3NCB, 4B and 4NCB using the RayStation treatment planning system with the Mevion beam characteristics and with the Monte Carlo calculation algorithm. PBS PT plans were made around the planning target volume (PTV). Target coverage and doses to the OARs (MHD, mean lung dose (MLD), contralateral breast (CLB) volume receiving ≥ 2Gy (V2)) were registered. Statistical analysis was performed using the one-sample Wilcoxon rank-signed test with a significance level of <0.05. Results Four out of 15 (27%) patients would have been accepted for PT according to the delta NTCP criteria. PTV coverage was fulfilled in all the plans (PTV V95% ≥ 99%). The increase from 2B to 3B resulted in a small but significant reduction in the MHD (p=0.041) as well as a decrease in the MLD (p=0.001). The addition of an extra beam, thus 4B

Conclusion Increasing the number of beams in BC PBS PT from 2 to 4 reduces significantly the doses to the OARs (MHD, MLD and V2 CLB), however with questionable clinical relevance. The use of non-coplanar beams does not improve the quality of the PBS proton plans. The perfect balance between reducing the dose to the OARs by using more beams and the time efficiency during PBS PT delivery is not clear and should be balanced out in a one by one basis. EP-1305 Long-term results up to 15 years after IORT boost in breast cancer patients E. Sperk 1 , M. Pez 1 , G. Welzel 1 , A. Keller 1 , Y. Abo- Madyan 1 , M. Ehmann 1 , B. Tuschy 2 , S. Berlit 2 , M. Sütterlin 2 , F.A. Giordano 1 , F. Wenz 1 1 University Medical Center Mannheim, Department of Radiation Oncology, Mannheim, Germany ; 2 University Medical Center Mannheim, Department of Gynecology and Obstetrics, Mannheim, Germany Purpose or Objective Intraoperative radiotherapy (IORT) given as a boost during breast conserving surgery (BCS) is one of the standard boost methods for breast cancer. This is the first report of a mature and detailed toxicity and outcome follow-up after IORT boost with 50 kV x-rays up to 15 years. Material and Methods Patients undergoing BCS plus IORT boost (med. 20Gy) and subsequent whole breast radiotherapy (WBRT, med. 46Gy) were included in this analyses. Follow-up was done twice yearly for 2 years and then yearly. Toxicity was evaluated according to a modified LENT SOMA scale (mod.: telangiectasia 0=no, 1=present). Cumulative (permanent >/=3 events during follow-up) toxicity rates were calculated using the Kaplan-Meier method. Cumulative outcome (local/axillary recurrence, second breast cancer, metastasis, overall survival) were assessed with the Kaplan-Meier method. Results Between 2002–2014, 400 breast cancers in 398 patients were treated with IORT boost (median age 63 years (30- 85y), median follow-up 78 months (2–180)). Median interval between IORT - WBRT was 48 days (13–377), main type was ductal/NST in 70.5%, lobular 24%, T0/1/2: 0.5%/73%/26%, N0/1/2/3: 76%/19%/4%/1%, M0/1: 99%/1%. Chemotherapy/endocrine therapy was given in 35%/83%. Permanent moderate/severe fibrosis was seen in 18.3/19.1/21.2% at 3/5/10y, permanent breast edema >°I in 2.4% at 5/10y, permanent ulceration >°I in 0.3% at 5/10y, permanent lymph edema of the arm >°I in 0.6/1.3% at 5/10y, permanent hyperpigmentation >°I in 0.5% at 5/10y, permanent pain >°I in 8.6% at 5/10y. Severe pain as first event was seen in 4% at 5/10y. Any telangiectasia as first event was seen in 18.3/23.2% at 5/10y. Our results