ESTRO 36 Abstract Book

S512 ESTRO 36 _______________________________________________________________________________________________

Purpose or Objective Locally advanced tumors with conservative surgery have a higher relapse rate than early tumors. We analyze the clinical outcome of HDR brachytherapy boost in patients at high risk for tumor size, in terms of local control, adverse effects and cosmetic results. Material and Methods Between February 1999 and October 2011, forty two patients with 43 tumours, consecutively diagnosed with cT3 infiltrative breast carcinoma were treated with neoadjuvant systemic treatment, conservative surgery and Whole Breast Irradiation (WBI) (50 Gy) followed by High Dose Rate (HDR) interstitial brachytherapy boost (3 x 4.4 Gy at 85% isodose) in two days, with rigid needles. Survival rates were calculated using the Kaplan-Meier method, and the Cox proportional hazards model to demonstrate the infuence of tumor response to neoadjuvant chemotherapy. Results Median age was 48 years (30-77). Median follow-up was 95 months (8-201). The average lesion size was 56.7 mm (50- 100) before receiving any treatment. Local Control (LC) at 5 and 10 years was 87.1%. Overall Survival (OS) at 5 and 10 years was 85.7% and 72.4% respectively. Cancer- Specific Survival (CSS) to 5 and 10 years was 85.7% and 75.8%. Disease-Free Survival (DFS) was 74,4% and 62,7% at 5 and10 respectively. Twenty-five tumor lesions (58 %) had a complete response after neoadjuvance. There were no significant differences in terms of local control depending on the tumor response to neoadjuvant chemotherapy (p = 0.66). Nor concerning overall survival (p = 0.52) or cancer- specific survival (p = 0.74). Grade 1 early toxicity was 38.5% and Grade 2 was 12.8%. There were no early Grade 3-4 toxicity. For late toxicity, 7/43 (16.3%) of patients had fibrosis. Some of the patients reported induration from surgery. There were no trophic skin changes. Good or excellent cosmesis was recorded in 95.3% of patients. Conclusion Adding HDR brachytherapy boost to conserving therapy allows preservation of breast in 87% of locally advanced breast tumors (cT3) at 10 years, with good cosmetic outcome. This technique is effective and well tolerated. PO-0925 Timing of post-implant analysis in permanent breast seed implant: results from a serial CT study E. Watt 1 , M. Peacock 2 , L. Conroy 1 , S. Husain 3 , A. Frederick 1 , M. Roumeliotis 3 , T. Meyer 3 1 University of Calgary, Department of Physics & Astronomy, Calgary- Alberta, Canada 2 University of British Columbia, Division of Radiation Oncology, Vancouver- British Columbia, Canada 3 University of Calgary, Department of Oncology, Calgary- Alberta, Canada Purpose or Objective Permanent breast seed implant (PBSI) is a novel, one-day procedure for the treatment of early-stage breast cancer. In this technique, stranded 103 Pd seeds are permanently implanted in a volume surrounding the post-lumpectomy seroma. Post-implant dosimetry is used to assess implant quality, but the timing for this analysis is performed inconsistently across cancer centres. The use of different time points for analysis limits the ability to combine results for long-term outcome studies. The purpose of this study is to determine the most appropriate timing for Ten patients underwent CT scans at 0 (immediately after), 15, 30, and 60 days post-implant. Each post-implant CT scan was deformably registered to the planning scan to obtain the seroma contour (clinical target volume, CTV) using MIM Maestro TM (MIM Software, Inc., Cleveland OH). This contour was reviewed and adjusted as necessary by a radiation oncologist. Using the TG-43 dose calculation formalism, a postplan was generated for each scan. For post-implant dosimetry. Material and Methods

Results The median plane Dmax dose was 1.33 Gy (40% of 3.4Gy, range 0.24-3.74 Gy) and showed moderate correlation with grade of skin marks (0.505, p value 0.000). Similarly, the closest distance of the CTV, prescription isodose (Figure 2) and first-last dwell position was 1.74 (range 0.32-6.58), 1.09 (range 0.02-5.71) and 1.55 (range 0.25- 4.58) cm respectively all of which also showed moderate correlation (-0.444, -0.471 and -0.495 respectively, p value 0.000 for each). 70.1% (61/85) planes with Dmax <40% of prescribed dose showed invisible or faint marks and 72.1% (62/88) planes with Dmax >40% of prescribed dose showed clear or prominent marks (p = 0.001). 86.4% (19/22) planes with closest distance from CTV <0.7 cm and 91.4% (32/35) planes with closest distance from 85% Isodose < 0.5 cm showed clear or prominent marks (p = 0.001). There was very high correlation between closest distance from CTV 0.7 cm and closest distance from isodose 0.5 cm (0.715). Taking 1.33 Gy (40% of prescription dose per fraction) as a cut –off value for plane Dmax resulting in clear-prominent implant marks on ROC curve resulted in sensitivity 65% and specificity 60%.

Conclusion This study highlights the need for minimization of dose to the skin E-E site for reducing the risk of clear or prominent skin marks which affect cosmesis. Wherever possible it is advisable to edit the CTV to maintain a safe distance between the prescription isodose from the skin E-E points. However, larger sample size needs to be studied to increase sensitivity and specificity of the E-E dose constraint. PO-0924 HDR boost in CT3 breast carcinoma with neoadjuvant chemotherapy and conserving therapy F. Romero 1 , J. Guinot 1 , M. Santos 1 , M. Tortajada 1 , P. Santamaría 1 , L. Oliver 1 , V. Campo 1 , L. Arribas 1 1 Fundación Instituto Valenciano de Oncología, Radiation Oncology, Valencia, Spain