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and 3 years. Acute toxicity was dermatitis G1 in 30% and G2 in 23%. Late effects were hypopigmentation or atrophy in 44.8%, telangiectasia in 20.6% and hyperpigmentation in 13.8%. Cosmetic outcome was registered in 25 cases, and it was considered good or excellent in 88%. Conclusion HDR contact brachytherapy is a good alternative to treat skin carcinomas on flat surfaces with good local control and acceptable cosmetic outcome. The hypofractionated scheme three times a week and right applicators tolerance, allows for a better compliance in elderly people. PO-1032 CT-guided interstitial BT of pulmonary malignomas. Retrospective analysis of 174 patients. P. Hass 1 , F. Sieber 1 , C. Willich 2 , M. Seidensticker 3 , T. Brunner 1 , J. Ricke 4 , K. Mohnike 5 1 University Hospital Magdeburg, Radiation Oncology, Magdeburg, Germany 2 University Hospital Jena, Radiation Oncology and Radiooncology, Jena, Germany 3 Ludwig-Maximilians-University, Clinical Radiology, Munich, Germany 4 Ludwig-Maximilians-University, Clinival Radiology, Munich, Germany 5 DTZ am Frankfurter Tor, Center for Radiology, Berlin, Germany Purpose or Objective Studies of recent years have shown that hypo- fractionated stereotactic radiation treatments of localized NSCLC and lung metastases can lead to high local control rates and thus also the chance to improve the overall prognosis. This study analyzed side effects and effectiveness as well as results of an alternative radiotherapeutic method. Material and Methods A retrospective analysis of 174 patients with metastases (156 patients, 89.6%) or primary NSCLC (18 patients, 10.4%) were treated with CT-guided interstitial HDR- brachytherapy (HDR-BT) in the period 03/2006-01/2015. A total of 359 lung malignomas were treated in 276 predominantly single-time brachytherapies. The number of malignomas ablated per single-time therapy was median 1 (1-7). Depending on the size of the lesion median 2 BT catheters (1-11) were administered. 56% of the metastatic patients suffered from a Colorectal Carcinoma (CRC), further 18% from renal cell carcinomas, mammary carcinomas and malignant melanomas. The tumor diameters varied between 5-134mm (median 18mm).The malignomas were irradiated with PTV enclosing single doses between 1.7-29.7 Gy (median 20.5 Gy). Patients received regular follow-up at intervals of 3, 6, 9 and 12 months after intervention, including contrast enhanced CT of the thorax. Side effects were recorded according to CTCAE criteria, survival data calculated using the Kaplan-Meier method. Results The local control rate (LCR) after 12 months was 77%, the 1-year overall survival (OS) 78%, the median OS 22.8 months.In the subgroup analysis, there are partially significant differences between the examined histological types (metastases of squamous cell carcinomas, adenocarcinomas, malignant melanomas, kidney cell carcinomas and other entities in the local control rate after 12 months (44%, 77%, 88%, 100%, 96%). As a result of the catheter application local bleeding occurred in 6 cases (2.2%, 1x °3 [CTCAE], promptly controlled by

angiographic coiling). In addition, uncomplicated pneumothorax °1/2 (CTCAE) were observed in 60 treatments (21.8%), 11.6% of these patients received a temporary suction drainage. In 5 cases (2.08%) pneumonitis was associated with typical radiological changes; antiinflammatory therapy was necessary in only The interstitial HDR-BT is a low-risk and effective radiation therapy option for the treatment of pulmonary malignancies. The pneumonitis rate is lower than for the SBRT. However, pulmonary malignomas with squamous cell origin showed a inferior local control rate, which consequentially led to an increase in the prescribed target dose (BED10> 120Gy) after completion of this study. PO-1033 Activation of specific anti-tumor immunity by alpha radiation based brachytherapy and immunotherapy Y. Keisari 1 , A. Cohen 1 , M. Efrati 1 , M. Schmidt 2 , R. Galalae 1 , I. Kelson 2 1 Tel-Aviv University / Faculty of Medicine, Clinical Microbiology and Immunology, Tel-Aviv, Israel 2 Tel Aviv University, School of Physics and Astronomy, Tel Aviv, Israel Purpose or Objective An innovative alpha radiation based brachytherapy termed Diffusing Alpha emitters Radiation Therapy (DaRT) was developed in our laboratories. Interstitial Radium-224 loaded seeds, release by recoil short-lived alpha-emitting atoms, which diffuse inside the tumor and spray a sizable fraction of it with highly destructive alpha radiation. DaRT provides, for the first time, an efficient method for treatment of the entire volume of solid tumors by alpha radiation. Insertion of such radioactive seeds into SCC tumors in human patients resulted in significant tumor regression. In experimental solid tumors in mice DaRT resulted in tumor necrosis and significant retardation of tumor growth, extended survival, reduced lung metastases, and activation of anti-tumor immunity. We explored approaches to boost systemic and specific anti-tumor immunity by combining DaRT tumor ablation with immunostimulation with CpG and neutralization of immunosuppressive cells such as regulatory T cells (Tregs) and myeloid derived suppressor cells (MDSC). Material and Methods Subcutaneous tumors from colon carcinoma origin (CT26) implanted in Balb/c mice, were treated with Ra-224 loaded stainless steel wires (seeds) with or without immunomodulating agents. Non-radioactive seeds (Inert) served as a control. Radiotherapy was delivered by intratumoral insertion of DaRT seeds (51-57 KBq/wire, Rn-220 desorption of 40-41%) in combination with the MDSC inhibitor, sildenafil, cyclophosphamide as a Treg inhibitor, and the immunostimulant, CpG. Tumor progression and the induction of anti-tumor immunity were determined. Results Treatment of animals by DaRT combined with CpG, sildenafil and cyclophosphamide significantly retarded tumor development. Tumor regression was observed in 80% of the mice (24/30) and 67% (20/30) of the tumors completely disappeared within 13-86 days. In the control group (Inert seeds + immunomodulators), 25% (3/12) of the tumors regressed and 8% (1/12) disappeared. The mice which their tumors regressed were reinjected with either CT26 or DA3 (breast carcinoma) cells. All DA3 two cases. Conclusion