ESTRO 37 Abstract book

ESTRO 37

S581

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

tumors developed within 10 days while the CT26 cells did not grew at all (52 days follow up). The specific resistance to tumor growth was proven to be immune response dependent. Transfer of spleen lymphocytes from CT26 bearing mice, cured by DaRT + immuno- modulating agents, protected naïve mice from the growth of CT26 cells. Conclusion Our alpha radiation based brachytherapy provides an efficient method for treatment of solid tumors by alpha radiation and also provides systemic activation of specific anti-tumor immunity. This combined treatment modality holds significant potential for the treatment of non- resectable human cancers PO-1034 High-dose-rate brachytherapy in the treatment of non-melanoma skin cancer. M.A. González Ruiz 1 , J. Quirós Rivero 1 , M.C. Cruz Muñoz 1 , J.J. Cabrera Rodríguez 1 , J.L. Muñoz García 1 , Y. Ríos Kavadoy 1 , M.F. Ropero Carmona 1 , A. Corbacho Campos 1 , F. García Urra 1 1 Infanta Cristina Hospital, Radiation Oncology Department, Badajoz, Spain Purpose or Objective To analyze the results in terms of overall survival (OS), cancer specific survival (CSS), local control (LC), cosmesis and toxicity in patients (pts) with non-melanoma skin cancer (NMSC) treated with high-dose-rate brachytherapy (HDR-BT) treatment, plesiotherapy modality; with radical or adjuvant intention in our hospital. Material and Methods Prospective study of 194 pts with 246 NMSC lesions, T1 (78.9%) and T2 (21.1%) stage treated from May 2015 to May 2017. HDR-BT treatment (6 Gy/fraction; total dose 42 Gy) was used in 88.2% pts with an equivalent 2 Gy dose (EQD2) of 56 Gy. Median total dose of HDR-BT was 42.6 Gy (range 36-50). All the lesions were limited 3-4 mm depth. The median age of the pts was 79 years-old (range 29-97); 61.4% males and 38.6% females. Basal-cell carcinoma (85.8%) was the most frequent histological type and most of lesions were T1 stage (78.9%). The 39.1% of the lesions were treated with Valencia applicators and 42.7% with custom-made moulds. Results The median follow-up was 20 months (range 2-61). The OS, CSS and LC was 94.7%, 100% and 95.1% respectively. There were no differences in terms of LC related with the type of applicator used (p 0.910) and with the T stage (p 0.149). The majority of pts had acute skin toxicity grade 1-2. Conjunctival toxicity appeared in 8.9 % of the pts. Cosmetic results were considered as excellent/very good in all patients. Conclusion Despite of the short follow-up, plesiotherapy treatment is a good alternative treatment which provides excellent results for local control and cosmesis (similar to the main studies) furthermore facilitates treatment compliance that is very relevant in elderly patients. HDR brachytherapy is a safe and attractive treatment option for non-surgical pts or when the cosmetic results are no good after surgery.