Abstract Book

S725

ESTRO 37

Purpose or Objective To estimate the impact of molecular subtype on locoregional failure in patients treated with adjuvant radiotherapy and contemporary systemic therapy Material and Methods We retrospectively analyzed data of patients with invasive breast cancer treated with adjuvant radiotherapy at our institution between 2005 and 2015. Molecular subtypes were defined as luminal A (LA), luminal B (LB), luminal Her 2, Her 2 and triple negative (TN) based on the 2015 St. Gallen Consensus Criteria. Survival estimates were calculated according to the Kaplan-Meier method at the end of the follow-up. The association of clinicopathologic features with local failure was evaluated using Cox proportional hazards regression models. Results 870 patients were analyzed. Molecular subtypes were distributed as follows: 58.5% LA, 21.2% LB, 8.4% luminal Her-2, 3.7% Her- 2, 8.2% TN. 86% of patient underwent breast conservative surgery (BCS), 11% mastectomy. Three hundred seventy six patients (43.2%) received adjuvant chemotherapy (antracyclines 70.5% and taxanes 51.3%). The majority of patients Her 2+ (67.6%) received trastuzumab immunotherapy . Sixteen (1.8%) loco- regional relapse occurred, 12 (75%) in breast/chest wall area, 2 (12.5%) in the nodal areas, 2 in both chest wall and nodal areas (12.5%). Median follow-up was 5.1 years (range 1-12 yrs). Non LA molecular subtypes showed earlier relapse compared to luminal A subtype (median time 39 vs 75 months). The actuarial 10-year local recurrence rate was 1.6% for LA, 4.3% for LB, 11.3 for Her2 and 7.8% for TN patients (p=<0.001). Univariate Cox regression revealed several factors associated with LR : age < 50 (p=0.03), N+ (p=0.04), high histologic grade (p=0.04). At multivariate analysis only high histologic grade (p=0.06) and molecular subtypes (p=0.02) were predictive of local recurrences. The 10-year metastases free survival rate of LA, LB, luminal Her2, Her2 and TN groups were 90.7, 82.4, 91.2, 90.5, 85.4% respectively (p=0.02). Conclusion Molecular phenotype has a significant impact on local and distant failure in patients with invasive breast cancer treated with radiotherapy and contemporary systemic therapy. Therefore, it should be integrated in adjuvant treatment decisions EP-1323 Dosimetry results and toxicity of a 3-week schedule RT with SIB in breast cancer, with TomoDirect M. Gerardi 1 , A. Morra 2 , S. Dicuonzo 2 , S. Arculeo 3 , F. Patti 3 , R. Ricotti 2 , V. Dell'Acqua 2 , M. Augugliaro 3 , C. Arrobbio 3 , A. Viola 3 , D. Rojas 3 , C. Fodor 2 , F. Emiro 4 , F. Cattani 4 , S. Raimondi 5 , V. Galimberti 6 , R. Orecchia 7 , M. Leonardi 2 , B. Jereczek-Fossa 8 1 Istituto Europeo di Oncologia, Radiotherapy Division, Biella, Italy 2 European Institute of Oncology, Division of Radiation Oncology, Milano, Italy 3 European Institute of Oncology and University of Milan, Division of Radiation Oncology and Department of Oncology and Hemato-oncology, Milano, Italy 4 European institute of Oncology, Unit of Medical Physics, Milano, Italy 5 European Institute of Oncology, Divisione di Epidemiologia e Biostatistica, Milano, Italy 6 European Institute of Oncology, Unità Senologia Molecolare, Milano, Italy 7 European Institute of Oncology and University of Milan, Department of Medical Imaging and Radiation Sciences and Department of Epidemiology and Statistics, Milano, Italy 8 European Institute of Oncology and University of Milan, Division of Radion Oncology and Department of Oncology and Hemato-oncology, Milano, Italy

Purpose or Objective to assess toxicity and cosmetic outcome in breast cancer patients treated hypofractionated radiotherapy to the whole breast plus simultaneously concomitant boost (SIB) using TomoDirect. Material and Methods 224 patients with early breast cancer treated with breast conserving surgery were given 40.05 Gy in 15 daily fractions, 2.67 Gy per fraction to the whole breast and 48 Gy in 15 fractions, 3.2 Gy per fraction, to the tumor bed with SIB. Acute and late toxicity and cosmetic were prospectively assessed during and after radiotherapy. Results The dose distribution within the breast was the following. Regarding the breast PTV, the median volume receiving the 95% of the prescribed dose was 99.2% (range 93.5- 100), the median maximum dose (D 0.03cc ) was 118% (range 113.8-125) and median value of prescribed dose delivered to 50% of breast volume was 102% (50-106), the median value of the breast volume receiving the boost dose prescription was 0.1% (range 0-13.6). Regarding the boost PTV, the median volume receiving the 95% of the prescribed dose was 97.6 ( range 70-100), the medium maximum dose was 102% ( range 100-6- 107). Acute toxicity evaluated at the end of radiotherapy, according to RTOG scale was the following. Concerning erythema, G0 was recorded in 14% and 36%, G1 in 73% and 56%, G2 in 13% and 8% on the whole breast (WB) and on the tumor bed (TB), respectively. Concerning desquamation, G0 was observed in 91.5% and 96.4%, G1 in 6.7% and 2.7 %, G2 in 1.8% and 0.9% on the WB and TB respectively. Concerning edema, G0 was seen in 78% and 84.4% and G2 in 22% and 16% on the WB and TB, respectively. One month afterwards (data available for 127 patients), G2 erythema was present in one patient (0.8%), while 14% and 12% of the patients showed G1 erithema on the WB and TB respectively. Grade 1 desquamation affected 3% of the patients, while G2 edema (symptomatic) affected one fourth of the patients. Late skin toxicity evaluation was available for 63 patients with a median follow-up was 14 months. The Table 1 showed the distribution of toxicity according to LENT-SOMA and cosmetic outcome. Analysis to correlate dose distribution and clinical features with toxicity is ongoing. Conclusion Hypofractionated RT with TomoDirect was characterized by high dose homogeneity and high PTV boost conformality, leading to limited maximum dose outside the PTV boost. Acute and early chronic toxicity were mild and acceptable. EP-1324 Hypo- vs Normofractionated RT in Early Breast Cancer – Patterns of Care in German speaking countries M. Mayinger 1 , K. Borm 1 , C. Straube 1 , D. Habermehl 1 , M.N. Duma 1 , S. Combs 1 1 Klinikum rechts der Isar- TU München, Department of Radiation Oncology, München, Germany Purpose or Objective Adjuvant radiotherapy (RT) plays an important role in early breast cancer management but the dose and fractionation schedules used are variable. A total whole breast irradiation (WBI) of 50/50.4 Gy in 25/28 daily fractions delivered over 5 weeks, usually followed by a boost is often considered the “standard” adjuvant RT prescription. Studies indicate that hypofractionated regimes such as 42.72 Gy in 16 daily fractions or 40.05 Gy in 15 daily fractions WBI are equally effective and achieve similar or better cosmetic and normal tissue outcomes. Thus, the 2017 German guidelines recommend hypofractionated RT (HF-RT) as a new standard of treatment for early breast cancer. However, there are