Abstract Book

S849

ESTRO 37

guided Ir-192 High dose rate brachytherapy from January 2007 to December 2016. All patients were first underwent to 3DCRT to whole pelvis with four field techniques. After 20Gy of EBRT, patients were received first dose of HDR brachytherapy and second HDR brachytherapy sitting were done after 40Gy of EBRT. A total of 46 Gy in 23 fractions of EBRT and 28Gy with HDR in two fractions were given to all patients. Results All patients were received total of 74 Gy dose, 46Gy with EBRT and 28Gy with HDR brachytherapy without any severe acute complications. The initial PSA rapidly decrease from median 56.065ng/ml to 14.7098ng/ml after one month of completion of treatment. The P-Value was ( p < 0.01; 2 tailed) which is statistically significant. Ten patients (2.08%) were complained of urethral structure which was removed by dilation. Sixteen patients (3.33%) had increase urinary frequency which was settled down between two to three months of the treatment. Five patients (1.04%) were complaining of urethral structure after second sitting of HDR brachytherapy. Conclusion The combination of EBRT with HDR brachytherapy is a good choice for the treatment of localized prostate cancer. It reduces overall treatment time, increase local biochemical control with low GU and GI toxicities. The results of the treatment are really dependent on Stage, risk group and age of the patients. EP-1577 Prostate cancer SBRT dose escalation to the dominant nodule/s: Phase I and immunological effects F. Herrera 1 , V. Valerio 2 , A. Harari 3 , B. Berthold 4 , J.Y. Meuwly 5 , V. Valle 6 , G. Coukos 7 , P. Jichlinski 2 , J. Bourhis 1 1 Centre Hospitalier Universitaire Vaudois, Department of Radiation Oncology, Lausanne Vaud, Switzerland 2 Centre Hospitalier Universitaire Vaudois, Department of Urology, Lausanne Vaud, Switzerland 3 Centre Hospitalier Universitaire Vaudois, Department of Oncology, Lausanne Vaud, Switzerland 4 Centre Hospitalier Universitaire Vaudois, Department of Oncology - Medical Oncology, Lausanne Vaud, Switzerland 5 Centre Hospitalier Universitaire Vaudois, Department of Radiology, Lausanne Vaud, Switzerland 6 Centre Hospitalier Universitaire Vaudois, Department of Radiation Oncology - Physicist, Lausanne Vaud, Switzerland 7 Centre Hospitalier Universitaire Vaudois, Department of Oncology - Ludwig Institute for Cancer Research, Lausanne Vaud, Switzerland Purpose or Objective To evaluate the tolerability and feasibility of irradiating the whole prostate gland with stereotactic body radiation therapy (SBRT) at doses of 36.25 Gy in 5 fractions while simultaneously escalating doses in the MRI visible- prostate dominant nodule/s up to 50 Gy. Material and Methods Patients (pts) eligibility: stage T2-3, N0, M0, Gleason Score≥6, prostate specific antigen (PSA)≤ 50, prostate volume ≤ 70 cm 3 , international prostate symptom score (IPSS)≤ 15, visible tumor/s at multiparametric (mp) MRI. Pts underwent the placement of a rectal spacer and a 3T MRI post- spacer insertion for planning purposes. Primary endpoint: Dose-limiting toxicity (DLT) defined as grade 3 or worse gastrointestinal (GI) and/or genitourinary (GU) toxicity by CTCAEv.4 within 90 days from the start of treatment. Main secondary endpoints: PSA, quality of life

(QLQC30, PR-25 bowel and sexual activity modules and IPSS questionnaires evaluation), and immunological responses before and after treatment. Peripheral blood mononuclear cells of human leucocyte antigen serotype A2 positive (HLA-A2+) pts were stimulated with PSMA, PSA, PSCA or PAP-derived peptides and tested for the release of interferon gamma (IFNγ) by ELISpot. Results Between 2014 and 2016, a total of 12 pts (5 high-risk and 7 intermediate-risk according to the D’Amico classification) were included in groups of 3. Pts received 45 Gy, 47.5 Gy, and 50 Gy in five fractions to the mpMRI visible dominant nodule/s. 11 pts were treated in CyberKnife and 1 patient in Tomotherapy. DLTs were not observed and thus MTD was not reached. Three additional patients were treated in the 50 Gy cohort without DLT. GI and GU toxicities by grade, cohort, and time point are summarized in Table 1. The median follow-up is 18.5 months (m) (range10 to 31 m). PSA control is 91.66% by the nadir + 2 ng/mL failure definition. The average (±SD) of the QoL assessments at baseline and at 3 m post- treatment for all patients were 83 (± 8) and 73 (±21) for QLC30 (mean difference, 10; 95% CI, 1.82-19.2), 1.4 (±4.8), and 5.9 (±8.4) for PR25 bowel module (mean difference, 4.51; 95% CI, 0.10-8.91), 42.4 (± 25) and 36.2 (±25.6) for PR25 sexual activity module (mean difference, 6.01; 95% CI, 0.2-12.39), and 6.5 (± 4.4) and 7 (±5) for IPSS (mean difference, 0.5; 95% CI, 0.3-1.3); respectively. ELISpot assay of 8 pts detected 5 pts with increase in the IFNγ secretion to HLA-A2-restricted prostate cancer peptides PSA, PSCA, PSMA or PAP.

Conclusion Irradiation of the whole prostate with 36.25 Gy in 5 fractions and dose escalation to 50 Gy to the dominant nodule has been completed without DLT. QoL analysis showed moderate impact in GU, GI and sexual domains. Longer follow-up will be necessary to confirm these preliminary results. A phase II trial is underway treating patients to 50 Gy in five fractions to the dominant nodule. SBRT can potentially enhance the IFNγ responses to prostate-specific antigens as demonstrated by the ELISpot assay. Comprehensive cell-mediated immune monitoring will be shown.