ESTRO 36 Abstract Book

S708 ESTRO 36 2017 _______________________________________________________________________________________________

control using mean decrease of PSA level during the different phases of follow up. In this study we have analyzed the results in the 77 patients with almost 3 months of follow up. Results All patients have completed CK SRT without severe complication. Median follow up was 17 months. Three patients died for non related cancer causes. Gastrointestinal acute toxicity G2 for perineal pain and rectal tenesmus was reported in only 13% and was decreased in all patients. Genitourinary acute toxicity G2 for urgency and nicturia was reported in only 4% and G1 for dysuria in 61% of cases which persist in 27,3% of patients. (Table 1) All patients obtained biochemical response with decrease of PSA. The PSA drop between the start of the therapy and at 21 months of follow up, was significant with p<0,01 (p=0,00001)

Conclusion Compared to MRI delineated GTVs, 18F-Choline PET GTVs are significantly different. This study found however that increasing the PET scan acquisition time from 60 to 90 minutes did not improve the performance of GTV TVD in comparison to MRI delineated GTV . EP-1334 Stereotactic radiotherapy with cyberknife® system in localized prostate cancer S. Falivene 1 , V. Borzillo 1 , R. Di Franco 1 , G. Totaro 1 , V. Ravo 1 , G. Quarto 2 , D. Sorrentino 2 , S. Perdonà 2 , P. Muto 1 1 Istituto Nazionale Tumori Fondazione Pascale, Radioterapia, Napoli, Italy 2 Istituto Nazionale Tumori Fondazione Pascale, Uorologia, Napoli, Italy Purpose or Objective Hypofractionated stereotactic radiotherapy (SRT) is an emerging technique in the treatment of localized prostate carcinoma (LPC). Considering that α/β ratio prostate cancer is very low (1.5), SRT is advantageous because consent to deliver higher dose/fraction on target respect conventional radiotherapy. In this study we reported our initial experience with SRT using CyberKnife® System (CK) in the treatment of LPC. Material and Methods From February 2013 to April 2016 ninety-six patients with LPC, mean age 70,6 years, were treated with CK-SRT. All patients were submitted to the eco-guided implants of 4 intraprostatic fiducial markers 7-10 days before the SRT in order to follow, to detect and to correct the intrafraction target movements. The fusion between CT scan and basal RM was made in order to optimize the contouring for treatment planning. All patients were treated with SRT in 5 fractions of 7-7,25 Gy/fraction for a total dose of 35-36,25 Gy. It was evaluated acute and late gastrointestinal and genitourinary toxicity using RTOG scale, biochemical

Conclusion In our experience CK-SRT seem to be safe and reliable in the LPC. No severe toxicities were reported and the patients were very compliant. Careful patient selection is critical to achieve maximum effectiveness by CK SRT. More patients and longer follow up are necessary in order to evaluate the real advantage of SRT respect to standard fractionation in terms of overall survival, biochemical free survival and late toxicity. EP-1335 Hypofractionated versus conventional radiotherapy in intermediate- to high-risk prostate cancer W. Guo 1 , X.S. Gao 1 , X.B. Gu 1 , M.W. Ma 1 1 Peking University First Hospital, Department of Radiation Oncology, Beijing, China Purpose or Objective Prostate cancer is one of the most common cancers in the world, and the population of patients with intermediate- to high-risk localized prostate cancer (PCa) occupies a large proportion. The results of treatment after hypofractionated radiotherapy only have been reported from several small randomized trials. Therefore, we pooled the relevant data and conducted a meta-analysis to compare clinical outcomes of hypofractionated