PO-0632 TOXICITY AND COSMETIC OUTCOME OF THREE-DIMENSIONAL CONFORMAL RADIOTHERAPY FOR PARTIAL BREAST IRRADIATION

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From different risk factors for toxicity (age, tumour size, hormonal therapy, chemotherapy, DHI) in univariate analysis only tamoxifen, was a significant factor for late toxicity (p = 0.009). Three local relapses (3%) were observed 19, 48 and 63 months after PBI. One regional relapse was observed in the supraclavicular and axillary nodes 7 months after PBI in a patient with negative sentinel node. Four patients developed distant metastases, 7 patients a contralateral breast cancer and 10 patients a second primary cancer. At the last check-up 90 patients were alive: 87 with no evidence of cancer, 2 with metastatic breast cancer, 1 with NSCLC. Ten patients died: 2 of metastatic breast cancer, 5 of another cancer, 3 of different causes. The 5-year probability of breast relapse-free survival, nodal relapse-free survival and cause specific-free survival were 97.7% (95% CI: 91.1-99.4), 99.0% (95% CI: 92.9-99.8) and 97.8% (95% CI: 91.7-99.5) respectively. Cosmetic results were excellent/good in 98 cases, fair in 2. Overall inter-rater agreement by physicians and patients on cosmesis was very good (K value = 1). Table 1: Late toxicity. Toxicity Skin, atrophy Skin and subcutaneous tissue induration/fibrosis Telangiectasia Pain Fat necrosis Seroma

Patients (total 25) 1 G3 10 (8 G1, 2 G2) 15 (11 G1, 4 G2) 3 G1 9 (8 G1, 1 G2) 3

Conclusions: Our data demonstrate that PBI with 192Ir interstitial multicatheter HDR brachytherapy is associated with a low late toxicity and relapses comparable to the best published results. PO-0631 INTER-FRACTION MOTION DURING 3D-CONFORMAL EXTERNAL BEAM ACCELERATED PARTIAL BREAST IRRADIATION A. Levy1, J. Autixier1, I. Dumas1, A. Boros1, C. El-Khoury1, V. Fallet1, C. Rossier1, A. Britten1, S. Heymann1, C. Bourgier1 1 Institut Gustave Roussy, Radiation Oncology, Villejuif, France Purpose/Objective: To assess the variation of inter-fraction motion throughout a course of 3D-conformal accelerated partial breast irradiation (3D-APBI) for breast cancer patients. Materials and Methods: 48 early breast cancer patients have been prospectively enrolled in a phase II 3D-APBI trial (total dose of 4042Gy in 10 BID fractions in one week) from October 2007 to March 2010. Inter-fractions motions were assessed by retrieving MV On-Board Imaging (OBI) was used to obtain internal tangent X-rays) at different and successive timepoints: before the first (F1), the fifth (F5) and the last fraction (F10) of 3D-APBI. All OBI were obtained through internal tangent photon beam and through anterior isocenter photon beam (0°) only for F1. Then all OBI were compared to baseline digitally reconstructed radiographs (DRR). Mean differences in breast position and standard deviation (SD) were analysed in lateral and vertical directions for each patient. Results: A total of 272 images were reviewed. Compared to baseline DRR, the mean inter-fractional movements in the lateral and vertical directions at F1 were 1.6mm (SD±1) and 1.5mm (SD±0.9), respectively; at F5, 1.8mm (SD±1) and 1.7mm (SD±0.8), respectively; and at F10, 1.4mm (SD±1) and 1.8mm (SD±0.7), respectively. When F1 was compared to F5, the differences of the mean inter-fractional movements in the lateral and vertical directions were 1mm (SD±0.7) and 1.2mm (SD±0.7), respectively. Between F1 and F10, the differences of the mean inter-fractional movements in the lateral and vertical directions were 1mm (SD±0.8) and 0.7mm (SD±0.5), respectively. Conclusions: Patients positioning during 3D-conformal APBI treatment through MV OBI performed at each fraction allow getting proper interfraction changes (1.1mm in any given direction). However, maximal movement can be as far as 3.6mm from baseline and inthis situation, should be taken into account in treatment planning. PO-0632 TOXICITY AND COSMETIC OUTCOME OF THREE-DIMENSIONAL CONFORMAL RADIOTHERAPY FOR PARTIAL BREAST IRRADIATION M. Gatti1, S. Bresciani2, R. Ponzone3, R. Panaia1, A. Salatino1, M. Stasi2, P. Gabriele1 1 Institute of Cancer Research, Radiotherapy, Candiolo, Italy

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Institute of Cancer Research, Medical Physics, Candiolo, Italy Institute of Cancer Research, Surgery, Candiolo, Italy

Purpose/Objective: the aim of this paper is to analyse the incidence of acute and late skin toxicity and cosmetic outcome in patients treated with three-dimensional conformal radiotherapy (3D-CRT) to deliver accelerated partial breast irradiation (APBI). Materials and Methods: A total of 84 patients were treated with 3DCRT for APBI. This technique was assessed in patients with low risk stage I breast cancer who were enrolled from September 2005 in an approved protocol of APBI. The prescribed dose was 34/38.5Gy delivered in 10 fractions twice daily over 5 consecutive days. Four to five no-coplanar 6 MV beams arranged tangentially to the breast were used, in particular five fields for left breast and four for the right one. On all CT scans Gross Tumor Volume (GTV) was defined around surgical clips. A 1.5 cm margin was added in order to account for microscopical invasion of the tumor by defining a Clinical Target Volume (CTV). A margin of 1 cm was added to CTV to define the planning target volume (PTV). The dose–volume constraints were followed in accordance with the specifications as dictated in the NSABP/RTOG protocol. After treatment, patients underwent a clinical and cosmetic evaluation every 3 months. Late toxicity was evaluated according to the RTOG grading schema. The cosmetic assessment was performed using the controlateral untreated breast as the reference (Harvard scale). Statistical analysis was performed in order to evaluate the correlation between dose escalation, irradiated volume and toxicities. Results: Median patient age was 66 years (range 51-87). Median follow-up was 21 months (range 2-66). The most common pathologic finding was invasive ductal carcinoma and the mean tumor size was 11 mm. The mean value of the ratio between the planning target volume and the whole ipsilateral breast volume was 38% and the median percentage whole breast volume that received 95% of prescribed dose was 34% (range 16%-55). The overall incidence of acute skin toxicities was 46% grade 1 and 1% grade 2. The incidence of late toxicity was 8% grade 1 and 4% grade 2. Grade 3 or greater toxicities were not observed. The most pronounced G2 late toxicity was telangiectasias, developed in three patients. Cosmetics results were excellent for 52% of patients, good for 42% of patients, fair for 5% of patients and poor for 1% of patients. There was no statistical correlation between rates of toxicities and prescribed doses (p=0.33) or irradiated volume (p=0.45). Conclusions: APBI using 3D-CRT is technically feasible with very low acute and late toxicity. Dose escalation is safe but long-term results are needed to assess its efficacy in reducing the incidence of breast relapse after conservative surgery. PO-0633 EARLY TOXICITY OF INTRAOPERATIVE ELECTRON RADIOTHERAPY AS TUMOR BED BOOST DURING BREAST CONSERVING SURGERY A. Wittig1, C. Hornickel1, U.S. Albert2, L. Zwiorek2, K. Zink1, R. Engenhart-Cabillic1 1 Universitätsklinikum Gießen und Marburg Philipps-Universität Marburg, Klinik für Strahlentherapie und Radioonkologie, Marburg, Germany 2 Universitätsklinikum Gießen und Marburg Philipps Universität Marburg, Klinik für Gynäkologie Gynäkologische Endokrinologie und Onkologie, Marburg, Germany Purpose/Objective: The early toxicity of intraoperative radiotherapy (IORT) as boost to the tumor bed during breast conserving surgery (BCS) followed by external beam radiotherapy to the whole breast (WBI) was evaluated and compared to the toxicity of postoperative EBRT to the whole breast followed by an additional EBRT boost. Materials and Methods: Between October 2010 and September 2011, a total of 154 early-stage breast cancers in 151 women were irradiated with IORT using 6-12 MeV electrons (10 Gy) followed by whole-breast EBRT (50.4 Gy). Patients were prospectively followed according to institutional standards for side effects (CTC-criteria) with regular clinical examination, photo-documentation and sonograpy when indicated. These data were retrospectively compared to a group of 150 patients with 153 breast cancers treated between January 2010 and September 2010 with 50.4 Gy WBI followed by an additional EBRTboost of 16 Gy. When indicated, adjuvant chemotherapy was given after BCS (+IORT) but before EBRT of the whole breast Results: Median follow-up was 8 months [range: 2-14 months]. Both groups were comparable with respect to median age (IORT-group: 60 years; range: 33-87 years, EBRT-group: 60.3 years, range: 38-86 years) and median tumor size (16.4 vs. 16.9 mm). In the IORT-group slightly