ESTRO 36 Abstract Book

S341 ESTRO 36 _______________________________________________________________________________________________

1 University of Tokyo Hospital, Radiology, Tokyo, Japan 2 St. Luke’s International Hospital, Radiation Oncology, Tokyo, Japan 3 Sonoda-kai Radiation Oncology Clinic, Radiation Oncology, Tokyo, Japan 4 St. Luke’s International Hospital, Breast Surgery, Tokyo, Japan 5 Breast Surgery Clinic, Plastic Surgery, Tokyo, Japan Purpose or Objective The use of post-mastectomy radiotherapy (PMRT) following immediate breast reconstruction has increased recently. However, its safety has not been well established. We aimed to evaluate the complication rates of PMRT to immediate tissue expander/permanent implant (TE/PI)-based reconstructions for breast cancer and its association with radiotherapy timing. Material and Methods From Jan 2003 to Dec 2014, breast cancer patients who underwent mastectomy, immediate TE/PI reconstruction and PMRT were retrospectively reviewed. The reconstructed breast and supraclavicular region were treated to a total dose of 50Gy in 25 fractions in most cases. Patients were divided into two radiotherapy timing groups, according to whether they received PMRT to a TE or a PI, to assess the effect of radiotherapy timing on complications. The rates of complications including reconstruction failure (RF), re-operation (unplanned removal or exchange of the TE/PI) and infection were estimated by Kaplan-Meier analysis. The risk factors including radiotherapy timing were analyzed by log-rank test and multivariate Cox proportional hazard model. Results A total of 81 patients were included. Of these, 32 patients (40%) received PMRT to the TE, and 49 patients (60%) received PMRT to the PI. Median age of patients was 44 years (range, 29-64). Median follow-up was 32 months (range, 2-120). Total RF, re-operation, and infection rates were 12.3% (10/81), 13.6% (11/81), and 11.1% (9/81), and 5-year cumulative RF, re-operation, and infection rates were 16.7%, 16.6%, and 12.2%, respectively. The median duration between PMRT and RF, re-operation and infection were 452 days (range, 14–1120), 474 days (range, 14–825) and 223 days (range, 9–654), respectively. No significant differences were observed in rates of RF, re- operation and infection with respect to radiotherapy timing ( P = 0.54, 0.73, 0.31, respectively). In univariate analysis, age ≥ 55 years was a significant factor for re- operation ( P = 0.009) and infection ( P = 0.046). In multivariate analysis, age 55 years and older was statistically significant for re-operation ( P = 0.02, HR (95% CI): 4.64 (1.27–16.9)) and infection ( P = 0.04, HR (95% CI): 4.6 (1.08–19.5)). Conclusion The overall RF rate was 12.3%. There were no significant differences in rates of RF, re-operation, or infection with regard to radiotherapy timing. PMRT to reconstructed breasts of older patients aged 55 years or over can be expected to result in more complications than in younger patients. PO-0653 A heart atlas for breast RT and the influence of delineation education on observer variability M. Kirli 1 , D. Akçay 1 , M.M. Barış 2 , I. Bilkay Görken 1 1 Dokuz Eylul Univ. Health Sciences Institute, RADIATION ONCOLOGY, IZMIR, Turkey 2 Dokuz Eylul Univ. Health Sciences Institute, RADIOLOGY, IZMIR, Turkey Purpose or Objective We developed a heart atlas for cardiac structure delineation for breast RT and intended to evaluate the influence of counturing education on contour accuracy and reduction of intra-inter observer variability and cardiac dose reporting.

Material and Methods The data from 16 early left breast cancer patients who received RT with deep breath hold technique in our clinic was analyzed. Heart and cardiac substructures (left (LCA) and right (RCA) coronery arteries, LAD, bilateral atrium and ventricles) were delineated by eight radiation oncologists. Then a cardiac atlas was developed on CT by a cardiac radiologist and experienced radiation oncologist. The whole heart and subunits were delineated for each patient and considered as a gold standard (GS) for this trial. The delineation was repeated on the same patients by observers after the atlas education. Standard tangential fields for RT were created on GS volumes for each patient and dose calculations were repeated for pre/post-atlas contours. The similarity was assessed by using Dice (DSC) and Jaccard (JSC) similarity coefficient indexes. The absolute difference rate was calculated for dose reporting analysis. The pre/post atlas data analyzed using Wilcoxon Signed-Rank test. Results The inter-observer similarity was increased statisticaly significant (SS) after education except just for RCA (p<0,05). Also the similarity comparing observers with GS increased in heart and all subunits with education. The increase for both similarity index in left atrium, bilateral ventricles, LCA+LAD has been found SS (p<0,05). There wasn’t a significant increase in heart contour similarity after training. We already obtained 94% of heart contour consistency, both pre-post atlas delineation which is higher than other studies in the literature. The intra- observer similarity showed a heterogeneous distribution but most of the observers made a delineation much more similar to GS. The absolute difference rate in dose reporting after using cardiac atlas was SS for bilateral atrium, right ventricle, LAD, LCA+LAD, RCA’s maximum (max) doses and bilateral atrium, right ventricle, and RCA’s mean doses (p<0,05). Although there was a SS increase for heart and left ventricle similarity rates by using cardiac atlas, it didn’t affect the dose reporting consistency. The max dose reporting differences from the GS decreased from 16,97% to 9.31% for LAD (p=0,011); from 14,78% to 9.31% for LCA+LAD (p=0,010). The mean dose reporting differences from the GS decreased from 34,97% to 22,25% for LAD (p=0.07); from 32,36% to 24,47% for LCA+LAD (p=0,056). The atlas usage was found to contribute to a more consisting dose reporting also for max and mean doses of atriums and right ventricle despite being on the edge and/or outside of the RT fields (p<0,05). Conclusion Cardiac atlas education and using for delineation on heart and subunits reduce the intra-inter observer variability and improves dose reporting consistency for left breast RT. PO-0654 Failure Patterns of Luminal B Breast Cancer Following Postoperative Adjuvant Radiation Therapy N. Choi 1 , S.W. Lee 1 , Y. Lim 1 , K.Y. Eom 1,2 , E.Y. Kang 2 , E.K. Kim 2 , Y.J. Kim 2 , J.H. Kim 2 , S.Y. Park 2 , I.A. Kim 1,2 1 Seoul National University Hospital Bundang Hospital, Radiation Oncology, Seoul, Korea Republic of 2 Seoul National University Hospital Bundang Hospital, Breast Care Center, Seoul, Korea Republic of Purpose or Objective The establishment of surrogate definitions for breast cancer molecular subtypes according to IHC has clinically demonstrated prognostic relevance for improved objective risk profiling and individualization of treatment regimens. Defining and stratifying luminal B subtypes, however, still remains indefinite and is in need of more distinct differentiation due to its heterogeneous clinical and molecular characteristics. This study aims to identify prognostic factors for early relapse in luminal B HER2- negative (LB HER2- ) and -positive (LB HER2+ ) subgroups, and to