Efficacy and toxicity from phase II study of dose escalation to intraprostatic tumor nodule in localized prostate cancer

102 Background: Intra-prostatic boost to dominant nodule is an attractive method for biological dose augmentation. Aim of study was to assess clinical feasibility of radiation boost to mp-MRI visible tumour using external beam radiotherapy. We report a planned analysis of toxicity and efficacy in the first two dose cohorts in this study. Methods: DELINEATE (ISRCTN04483921) was a single centre prospective phase 2 multi-cohort study including standard (Cohort A (A): 74Gy/37F) and moderately hypofractionated (Cohort B (B): 60Gy/20F) prostate image-guided IMRT regimens. Patients treated in A and B received integrated boost of 82Gy and 67Gy to mp-MRI-visible lesions. 55 patients were recruited to A and 158 patients recruited to B; the first 50 sequentially treated patients in B were included in analysis. Duration of androgen deprivation therapy was at clinician discretion. Primary endpoint was RTOG late toxicity at 1 year. Secondary endpoints included acute and late toxicity timepoints and biochemical relapse (BCR) free survival, using Phoenix definition. Treatment related toxicity was measured by RTOG, CTCAE v4 scales, IPSS and EPIC-26. Results: Between July 2011 and January 2015, 105 patients were treated within A&B. Median follow up for A was 74.5 months and 52 months for B. Median age was 71 years (range 57-80). In A and B, there were 27% and 40% of patients respectively classified with NCCN high risk disease. Cumulative RTOG toxicity in Table. 6 patients had BCR (5 patients: A and 1 patient: B). Within A, 1 patient had pelvic nodal progression and 1 local progression; patient in B had local progression. Conclusions: Delivery of intra-prostatic boost to dominant nodule is feasible with acceptable toxicity and good efficacy. Intra-prostatic boost is now part of the randomised phase 3 PIVOTALboost trial (ISRCTN80146950). Clinical trial information: 04483921. [Table: see text]