Abstract Book

S705

ESTRO 37

(2 Gy/fraction) to the whole breast and an additional simultaneous 10 Gy (2.4 Gy/fraction) to the tumor bed over 25 fractions Results 139 patients (median age: 50, range: 29-79; pT1N0: 82.1%, pT2 N0: 16.5%, pT3 N0: 0.7%, pT4 N0:0.7%) were enrolled and analyzed. 38% of patients underwent previous chemotherapy. The TAC rate was as follows: G1: 32.4%, G2: 33.1%, G3: 2.9%. Mild hematological toxicity was registered in 2.2% of patients. Twenty four-months grade 1 TTC and TTSC free survival were 47.8% and 68.3%, respectively with no higher grade TTC and TTSC observed. Four patients (2.8%) had radiological findings of lung toxicity. With a median follow-up of 18-months (range: 5-83), no patient showed local or nodal An hybrid IMRT class solution produced negligible severe TAC as well as TTC and TTSC with an excellent local- regional control in patients with low-moderate risk of recurrence invasive breast cancer EP-1282 Complication analysis of breast cancer patients treated with mastectomy with IABR and PMRT L. So Jung 1 1 Incheon St. Mary's hospital, Radiation oncology, Incheon, Korea Republic of Purpose or Objective To investigate the complication rates and time to complication after mastectomy with immediate autologous breast reconstruction (IABR) and adjuvant radiotherapy (RT) in breast cancer patients. Material and Methods Between April 2009 and January 2017, 52 patients underwent mastectomy with IABR followed by adjuvant RT. We retrospectively reviewed the medical records of these patients. All complications that occurred from RT initiation date were analyzed. The complications were classified into the following 4 types: Re-operation for breast reconstruction, revisional surgery, fat necrosis, and wound infection. We also evaluated the factors that may be associated with complication such as flap size, body mass index (BMI), interval between adjuvant RT and IBR, boost RT, and dose homogeneity index (DHI). RT was delivered on the chest wall, including flap in all patients. The extent of ipsilateral axilla as well as supraclavicular and internal mammary region were included by the physician’s discretion. Median RT dose was 50.4 Gy (range 50.4 – 64.8 Gy). Results In total, 52 stage IIA-IIIC breast cancer patients were analyzed, and median follow up duration was 18.2 months (range 1.8-98.6 months). All patients underwent neo-adjuvant or adjuvant chemotherapy and neo- adjuvant chemotherapy was performed in 22 patients (42%). Delayed nipple areolar complex reconstruction was performed in 22 patients (42.3%). Overall complication rate was 17.3%. Three patients (5.8%) required revisional surgery to manage complication. Two of them underwent reconstruction over again using implant. Fat necrosis occurred in 9 patients (17.3%). There was no wound infection. The median time to first occurrence of complication after RT was 8.6 months (range 1.8-25.1 months). Two-thirds of the complications occurred within 1 year after RT and 88.9% of them occurred within 2 years. Larger flap size (≥ 542g) did not show any significant correlation with occurrence of complication. Also, there was no significant correlation between complication and the interval (> 6 months) between breast reconstruction and RT initiation, the boost RT, and DHI. Conclusion IABR and adjuvant RT may be performed with acceptable complication. Most of the complications occurred within recurrence Conclusion

2 years of RT initiation and complication occurrence was decreased with time. EP-1283 Lung sparing techniques for internal mammary chain radiotherapy in right breast cancer patients A. Ranger 1 , C. Perotti 2 , A. Dunlop 3 , E. Donovan 4 , H. McNair 5 , E. Harris 3 , A. Kirby 1 1 ICR and Royal Marsden NHS Foundation Trust, Clinical Oncology, Sutton, United Kingdom 2 The Royal Marsden NHS Trust, Breast Oncology, London, United Kingdom 3 ICR and Royal Marsden NHS Foundation Trust, Physics, Sutton, United Kingdom 4 University of Surrey, Centre for Vision Speech and Signal Processing, Guildford, United Kingdom 5 ICR and Royal Marsden NHS Foundation Trust, Radiotherapy, Sutton, United Kingdom Purpose or Objective The use of internal mammary chain radiotherapy (IMC-RT) is increasing. Inclusion of the internal mammary chain (IMC) in the radiotherapy target volume results in an absolute increase in ipsilateral lung V 17 Gy (Volume of lung receiving 17 Gy) of approximately 10% (Offersen et al, 2014). For patients with left breast cancer, use of deep inspiratory breath hold techniques (DIBH) is standard within most departments in order to reduce heart doses. Dosimetric studies suggest that treatment in DIBH also reduces ipsilateral mean lung dose for right-breast- affected patients requiring IMC-RT (Poortmans et al, 2015). However, due to the increased linear accelerator time associated with use of DIBH, not all RT centres are able to adopt DIBH techniques for right-sided breast cancer patients requiring IMC-RT. An alternative approach to reducing lung dose in patients undergoing field-based IMC-RT is to displace the match-plane between the tangents and the nodal fields superiorly. This dosimetric study compares the lung-sparing ability of the superior match-plane move against that of a DIBH technique. Material and Methods Fourteen previously treated patients who had CT planning scans in DIBH and free breathing (FB) were planned using three techniques: wide tangents (WT) in FB with a standard match-plane, WT in FB with a superior match- plane and WT in DIBH with a standard match-plane. The standard match-plane was placed at the inferior aspect of the medial head of the clavicle. The superior match- plane was placed one CT slice (3mm) below inferior aspect of the head of the humerus (Figure 1). Target volumes included the right axillary lymph node levels 1-4, whole breast and IMC (delineated according to ESTRO consensus guidelines). Ipsilateral lung V17 Gy , IMC and axillary nodal target volume dose statistics were compared between groups using a one way ANOVA with Bonferroni correction for multiple comparisons (significance level =0.05).

Results There was no significant difference between target volume coverage for the three techniques. The