Abstract Book

S866

ESTRO 37

Results Forty patients (95.2%) in group 1 had developed urinary toxicity which was greater or equal to grade 2 in 8 cases (19.1%). In group 2, 38 patients (90.5%) had developed urinary toxicity which was greater or equal to grade 2 in 9 cases (21.4%). The difference between the 2 groups was not significant (p = 0.39). Gastrointestinal toxicity was observed in 13 patients (30.9%) in group 1 and 23 patients (54.8%) in Group 2 with a significant difference (p = 0.02). This toxicity was greater or equal to grade 2 in 3 cases (7.1%) in group 1 and in 2 cases (4.8%) in group 2. Conclusion Curative treatment of prostate cancer in the elderly is controversial. In fact radical prostatectomy is rarely proposed to patients aged over 70 years. Conformal radiation therapy seems to be effective and well tolerated alternative for this population. Current published data show that high-dose radiation therapy (≥70 Gy) is not more toxic for older compared to younger subjects. The results of our study are consistent with the literature. Age should not be a limiting factor for conformal radiation therapy in curative intent for older patients. EP-1609 Circulating hematopoietic progenitor cells and endothelial cells in prostate cancer under SBRT C. Cigarral García 1 , L.I. Sánchez-Abarca Bernal 2 , C. Rodríguez Serrano 2 , V. Macías Hernández 1 , M.P. García Rodríguez 1 , M.C. Hernández Corral 1 , B. Vidriales Vicente 2 , F. Sánchez-Guijo Martín 2 , L.A. Pérez-Romasanta 1 1 IBSAL-Hospital Clínico Universitario de Salamanca, Radiation Oncology Department, Salamanca, Spain 2 IBSAL-Hospital Clínico Universitario de Salamanca, Hematology Department, Salamanca, Spain Purpose or Objective Blood circulating hematopoietic progenitor cells (CPCs) and circulating endothelial cells (CECs) are two cell groups that appear to play a key role in tissue vasculogenesis. Quantification by flow cytometry of CECs has been shown to have prognostic value in a number of neoplastic diseases. The quantification of CPCs and CECs after stereotactic-body-radiation-therapy (SBRT) for prostate cancer has not been established. This was the main objective of the current study. Material and Methods This prospective study was conducted on 10 patients diagnosed of prostate cancer that underwent SBRT in our Institution. Mean age was 71 years (range 58-76). The main SBRT schedule was 45.20Gy in 8Fx (BED 1.5 = 92.34Gy) delivered with IMRT in Tomotherapy unit in all cases. Endorectal balloon was used in all patients to limit prostate intra-fraction motion during treatment and to decrease the volume of rectum and anus receiving high dose radiation. Peripheral blood samples were collected on the first day of treatment (baseline), in the middle, the last day (end) and after 40 or 50 days (1.5-months follow-up) after the end of SBRT. Samples were stored at room temperature until analyzed. Quantification of CPCs and CECs was performed by flow cytometry to detect and quantify different cells subsets and their kinetics at above mentioned times. The GraphPad software was used for the statistical analysis. Results CPCs were defined as CD34++/CD45dim/CD31+. Compared to baseline values, a significant reduction of total CPCs (1994.23 vs 1090.41 CPCs/µl; p=0.003) at the end of SBRT was observed. No significant differences were observed in the quantification of total CPCs at +40-

50 days after SBRT compared to baseline values (1994.23 vs 1931.02 CPCs/µl; p=0.67). CECs were defined as CD146+/31+/34+/CD45-. Tumor derived endothelial cells (TECs) were defined as CD45-/CD31++/CD276+. Compared to baseline values, no significant changes of total CECs and TECs numbers after SBRT were observed in any of the time-points evaluated. Conclusion In this study we have been able to quantify CPCs and CECs with a reproducible protocol in prostate cancer patients after SBRT. Preliminary results show a significant reduction in CPCs at the end of treatment that may be related to low doses of pelvis irradiation with IMRT technique. There were no significant changes in the total CECs and TECs during SBRT. Funding: This study has been partially supported by grant GRS1106/A/15, from Gerencia Regional de Salud de Castilla y León (Spain). L. Marinelli 1 , C. Reverberi 1 , L. Nicosia 1 , S. Magrini 2 , S. Giacinti 2 , G. Poti 2 , G. Arrivi 2 , M. Osti 1 , V. De Sanctis 1 , C. Proietti 1 , A. Aschelter 2 , P. Marchetti 2 , M. Valeriani 1 1 Azienda Ospedaliera Sant' Andrea, Department of Radiation Oncology, Rome, Italy 2 Azienda Ospedaliera Sant' Andrea, Department of Oncology, Rome, Italy Purpose or Objective The effectiveness of abiraterone acetate has been demonstrated both in pre- and post-chemotherapy settings in mCRPC patients. Oligoprogression during abiraterone treatment might not represent a systemic strategy failure. Combining a local treatment, as radiotherapy, could permit to continue the systemic therapy and delay line shifts of curative strategies aiming to improve clinical outcomes. The purpose of our study is to demonstrate the efficacy of adding radiotherapy to abiraterone treatment in oligoprogressive mCRPC patients. Material and Methods From June 2014 to August 2017, 12 consecutive mCRPC patients treated with Abiraterone undergone curative/palliative radiotherapy for oligo-progression (1-3 sites). All patients presented increasing PSA demonstrated on 3 consecutive evaluations. Oligo- progression was confirmed with F-Choline PET-TC and with contrast enhanced MRI for patients scheduled for stereotactic radiotherapy. Four patients (33.3%) were treated with stereotactic radiotherapy (27 Gy in 3 fractions) and 8 (66.7%) with 3-D conformal palliative radiotherapy (20 Gy in 5 fractions or 30 Gy in 10 fractions). Fractionation was chosen based on the extension of lesion. All patients presented skeletal secondary localizations so bone was the unique site of metastasis. A total of 14 bone lesions were treated (2 patients presented 2 lesions). After radiotherapy all patients continued Abiraterone therapy. Results Median follow-up from the start of abiraterone was 23.7 months (range 10.5-35.7 months). Median actuarial overall survival (OS) was not reached. Actually 3 patients (25%) are dead with disease, 6 (50%) are alive with disease and 3 (25%) are alive without disease. Median duration of abiraterone treatment was 12.7 months (range 6.2-30.9 months). Median duration of Abiraterone after RT was 4.9 months (range 2.2-23.6 months). Median progression-free survival (PFS) calculated from EP-1610 Oligoprogression during Abiraterone therapy treated with radiotherapy in mCRPC patients.