Abstract Book

S206

ESTRO 37

Material and Methods From March 1999 to June 2017, 33 patients with histologically confirmed IBTR (29 T1, 2 Tis and 3 T2) were treated with interstitial HDR brachytherapy ( 192 Ir) after tumour re-excision as an alternative to salvage mastectomy. All patients had prior lumpectomy followed by standard EBRT for early stage breast carcinoma (dose range 50-66 Gy). The median time from first treatment was 10 years (range 2-25). All were retreated with conservative surgery with (10) or without (23) SLN biopsy. Two had DCIS, 3 had ILC, 21 had IDC, 3 had tubular carcinoma, two had IDC c-erb 3+ and 2 had IDC plus DCIS >25%. The median diameter of infiltrating tumour was 12 mm (range 3-28 mm). The recurrent tumours were excised with final margins of resection free of residual disease per National Surgical Adjuvant Breast and Bowel Project (NSABP) definition. In 30 of 33 patients tumour bed implantation was performed, during the surgical procedure, using an interstitial catheters technique: plane, number and spacing catheters were individually chosen to cover the width and thickness of the lumpectomy cavity; all patients but one (1 plane) had two planes and the median number of catheters was 8 (range 5-11). In 3 patients the procedure was done after surgery. The tumour bed plus 1.0 cm clinical margin represented the target volume. The dose delivered to the target volume was 40-50 Gy (2.5 Gy BID) for the first 15 patients (2D planning) and 34 Gy (3.4 Gy BID) for the last 18 patients (3D planning). Results The procedure was well tolerated by all patients. Only two patients developed a wound infection two/three months after the procedure, with final bad cosmetic outcome; no other complications related to the implant, such as bleeding or infection, were observed. Median follow up was 56 months (range 4-223). The local control was 87%, in the 2D group, and 95% in the 3D group, with three local relapses (respectively, 2 and 1). Global DFS was 94%. Five patients had adjuvant CT and 28 had adjuvant OT (6 Tamoxifen and 22 aromatase inhibitors) and 2 patients had targeted therapy (trastuzumab). Cosmetic results defined by the NSABP cosmesis scale were satisfactory for the first 13 patients and excellent for the last 18 patients. One patient developed a localized seroma with spontaneous resolution after 18 months, 5 patients had fibrosis and telangiectasia (Grade 2 using CTCAE v3.0), and the other patients had good or excellent cosmetic results. Conclusion Our retrospective mono-institutional experience shows that a second conservative strategy, using lumpectomy followed by interstitial BT HDR is a feasible treatment for IBTR and may represent a valid alternative to salvage mastectomy, offering very low complication rate and good cosmetic results, provided strict selection criteria are used for patients selection. OC-0403 Second ipsilateral breast tumor event: impact of the GEC-ESTRO APBI classification L. Montagné 1 , J. Gal 2 , M.E. Chand 1 , M. Gauthier 1 , J.M. Hannoun-Levi 1 1 Antoine Lacassagne Center, Department of Radiation Therapy, Nice, France 2 Antoine Lacassagne Center, Biostatistic Unit, Nice, France Purpose or Objective Second ipsilateral breast tumor event (2 nd ILBTE) occurring after primary radio-surgical treatment can be treated either by salvage mastectomy or 2 nd conservative treatment (2 nd CT) including an accelerated partial breast re-irradiation (APBrI). We analyzed the impact of the GEC-ESTRO APBI classification (GAC) on the oncological outcome after APBrI.

Material and Methods Between 2000 and 2016, 159 patients (pts) underwent a 2 nd CT at our center. After lumpectomy, APBrI was performed using either low (30 – 55 Gy on the reference isodose) or high dose-rate brachytherapy (16 to 34 Gy). Oncological outcome including 3 rd ILBTE, regional [RFS] or metastasis free survival [MFS], specific [SS] and overall survival [OS] was analyzed according to GAC. Univariate (UVA) and multivariate analyses (MVA) were conducted to identify significant prognostic factors for 3 rd ILBTE. Results With a median follow-up of 71 months (range: 62 - 85 months), 60 pts (42%), 61 pts (42.7 %) and 22 pts (15.4%) were classified as low (LR), intermediate (IR) and high- risk (HR) respectively. For the whole cohort, 5-year 3 rd ILBTE free survival, RFS, MFS, SS and OS rates were 98.9%, 97.6%, 91.5%, 95.5% and 93.8% respectively. 5- year 3 rd ILBTE free-survival rates for LR, IR and HR were 100%, 100% and 92.9% respectively (p = 0,003). 5-year RFS, MFS, SS and OS rates according to GAC are reported in Table 1. In UVA, vascular embolisms (p = 0.008) and GAC (p = 0.001) were considered as significant prognostic factors for 3 rd ILBTE, while, in MVA, GAC (p = 0.008) was the only prognostic factor.

Conclusion In case of 2 nd ILBTE, GAC could be used as a helping- decision tool to discuss conservative or radical treatment options.

Proffered Papers: PH 7: Dose measurement and dose calculations

OC-0404 Rationale for AAPM recommendations on medium for TPS reference dose specification S. Kry 1 , V. Feygelman 2 , P. Balter 1 , T. Knoos 3 , C. Ma 4 , M. Snyder 5 , B. Tonner 6 , O. Vassiliev 1 1 UT MD Anderson Cancer Center, Radiation Physcis, Houston- TX, USA 2 Moffitt Cancer Center, Radiation Oncology, Tampa, USA 3 Skane University Hospital, Radiation Oncology, Lund, Sweden 4 Fox Chase Cancer Center, Radiation Oncology, Philadelphia, USA 5 Wayne State University, Radiation Oncology, Detroit, USA 6 Ackerman Cancer Center, Radiation Oncology, Fernandia Beach, USA Purpose or Objective Reference dose calibration has be done as “dose-to- water” or “dose-to-muscle”. At present there is no consistency in the community about which is ideal or how the solution should be clinically implemented. Consequently, there is an additional +/- 1% spread in different reference calibrations. While this is a small uncertainty, it impacts calibration and systematically affects the dose delivered to all patients. As such, a consistent and reasonable approach should be undertaken