Abstract Book

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ESTRO 37

imaging, bangalore, India 4 Healthcareglobal enterprises limited, radiation oncology, bangalore, India Purpose or Objective PSMA PET-CT imaging is becoming more important as a quantitative monitor of individual response to radiation therapy. Response of tumors to therapy has been traditionally assessed by changes in size and dimensions of tumor(s) in CT images (RECIST Criteria). However, change in size because of therapy may take many months to develop and any opportunity to make early decisions about success or failure of therapy is often unduly delayed or lost altogether.Independent measures of changes in metabolic activity (SUV-Standard uptake values) via PSMA PET-CTs can provide an alternative to 18 F-fluorodeoxyglucose (FDG), 11 C-acetate (ACET), 11 C- or 18 F-choline (CHOL), anti-1-amino-3- 18 F- fluorocyclobutane-1-carboxylic acid (FACBC) to assess response to radiotherapy. In this study we evaluate the utility of PSMA PET in assessing response to radiotherapy in High Risk organ confined prostate cancer. Material and Methods total of 43 patients with organ confined biopsy proven high risk prostate cancer patients with Ga-68 PSMA PET- CT done at two time points with first at diagnosis and second at one year post external beam radiotherapy were considered and retrospectively evaluated from 2014 to 2016 .All patients received IG-IMRT technique to Prostate, seminal vesicles with prophylactic irradiation of pelvic lymph nodes. Quantification of metabolic response to radiotherapy was based on comparison of baseline SUVs with SUVs of PSMA PET-CT scan done at one year and subsequently relating the same with PSA levels at baseline and one year with PSA levels >2ng/ml considered as biochemical relapse based on Phoenix definition post radical radiotherapy treatment .Data was analyzed using SPSS version 18 for windows. Sensitivity, Specificity, Positive Predictive value and negative predictive values were determined. Spearman’s correlation coefficient was used to determine bivariate relationship between change in PSA values and SUV following radiotherapy treatment Results The results suggest that PSMA PET had a high sensitivity 100% (95% CI 87%-100%) but low specificity 33% (95% CI 9%-69%) in detecting biochemical response or failures following IG-IMRT treatment of organ confined prostate cancer. The positive predictive value was 85% and negative predictive value was 100%. There was a significant positive correlation between change in PSA levels following treatment versus change in SUV (r = 0.52, The results suggest utility of PSMA PET as a molecular imaging marker in assessing prognostication following radiotherapy treatment of organ confined prostate cancer. The low specificity with biochemical response needs to be validated with repeat biopsy following treatment in those patients where PSA levels increased despite fall in SUV uptake. EP-1567 Systematic review and meta-analysis of conventional vs hypofractionated radiotherapy in prostate p < 0.001). Conclusion

oligorecurrences (BM) from metastatic Castration Sensitive Prostate Cancer (mCSPC) after primary treatment. Material and Methods We retrospectively collected data of pts treated to BM from mCSPC with SBRT between 03/2012 and 11/2016. Inclusion criteria were: < 5 lesions at time of SBRT detected with positron emission tomography/computer tomography (PET/CT), Magnetic Resonance Imaging (MRI) and CT; hormone-naïve disease at first extra-regional localization; no evidence of local recurrence. Prostate Specific Antigen (PSA) was measured every 3 months after SBRT. Biochemical outcome was assessed according to PSA level variation (ΔPSA) between pre-SBRT and post- SBRT: biochemical response (BCR) was defined as ΔPSA < -20%, progression (BCP) as ΔPSA>+20% and stability (BCS as 20%<ΔPSA<+20%). Imaging was performed in case of BCP. Treatment toxicity was evaluated according to Common Terminology Criteria for Adverse Events version 4 (CTCAE v.4.0). The impact of potential predictive factors on biochemical and clinical progression free survival (b- and c-PFS), local control (LC), prostate cancer specific survival (PCSS) were estimated by Cox- proportional regression. Survival analysis was performed with Kaplan-Meier (Log-Rank test) approach. Results Seventy-seven BM were treated in 55 pts. Median age, initial PSA (iPSA) and pre-SBRT PSA were 72 years, 9.12 ng/mL and 3.5 ng/mL, respectively. Median dose was 24Gy/3 fractions. Twenty-five pts (45%) received SBRT alone while the remaining 30 pts (55%) received concomitant SBRT and ADT. Median follow-up was 17.9 months (range: 3.0-55.0 months). No acute or late toxicity of grade≥2 was reported. BCR, BCS and BCP were observed in 33 (60%), 11 (20%) and 11 (20%), respectively. Clinical progression was observed in 28 (51%) pts after a median follow-up of 7.0 months (range: 2.9-34.0 months). In-field progression occurred in 9 (12%) BM. One-year b-PFS, c-PFS and LC rates were 54%, 55% and 92%, respectively. One- and two-year PCSS rates were 100% and 96%, respectively. Comparing subgroups of patients treated with SBRT alone and with concomitant ADT, b-PFS and LC were significantly lower in the former (p=0.035 and p=0.002). On the contrary, c-PFS was similar (p=0.2908). In pts treated with SBRT alone, ADT was administrated after a median time of 8.4 months from the SBRT. At the last follow-up, 14 pts were alive with no evident disease (25.5%), 36 pts were alive with disease (65.5%), 3 pts died for cancer related death (5.5%), and 2 pts died for other causes (3.5%). Conclusion SBRT is safe and allows high one-year LC rate (92%). One out of 2 pts was free of progression one year after SBRT. Addition of ADT to SBRT improved b-PFS and LC, but not c-PFS. Further investigation is warranted to identify pts that could benefit most from this treatment modality and the optimal combination with androgen deprivation or other systemic treatments. EP-1566 Metabolic response assessment using Ga68 PSMA PETCT in HR organ confined Prostate cancer post IGIMRT G. Lohith 1 , S. Shivakumarswamy 2 , K. Kallur 3 , G. Prashanth 3 , K. Kumarswamy 4 , S. Bhattacharjee 4 , R. Billimaga 4 , K. Gurunath 4 , A.K. Basavalinga 4 1 HCG hospitals, Radiation Oncology, Bangalore, India 2 healthcareglobal enterprises limited, radiology, bangalore, India 3 healthcareglobal enterprises limited, functional

N.R. Datta 1 , E. Stutz 1 , S. Rogers 1 , S. Bodis 1 1 Kantonsspital Aarau, Radio-Onkologie, Aarau, Switzerland