ESTRO 2020 Abstract Book

S1086 ESTRO 2020

Results There were no episodes of grade 4 or 5 toxicity. 35 (33.33%) grade 2-3 acute and 17 (16.67%) grade 2-3 late toxicities were observed in the group treated before the introduction of the bladder neck structure. There were 17 (16.35%) and 8 (14.04%) respectively afterwards. This corresponded to a statistically significant absolute difference of 16.98% in acute toxicity (p=0.005) The 2.63% absolute difference in late toxicity was not statistically significant (p=0.66). 3 (2.86%) patients developed urinary retention prior to use of the bladder neck and 1 (0.96%) developed this complication afterwards. A small number of patients had a ‘bladder neck’ volume of less than 2cc so no result for the DVC was available. Acute grade 2 or above toxicity developed in 11/62 (17.74%) of those with a D2cc >50% and 4/32 (12.5%) of those with D2cc <50% (absolute difference 5.24%;p=0.51). Late grade 2 or 3 toxicity was seen in 6/37 (16.2%) vs 0/14 (0%) – an absolute difference of 16.2% ( p=0.11). There was a slight but non-significant reduction in bladder neck D2cc dose over time after contouring of the OAR began. Conclusion We saw more grade 2 and above toxicities in those who had prostate seed implants before we began contouring the bladder neck structure. The results were statistically significant for acute urinary toxicity. There was a trend towards better outcomes for those with a recorded bladder neck D2cc <50%, particularly for late toxicity. We believe this validates the use of bladder neck D2cc in prostate seed brachytherapy. 1. 1. Harthout L, et al. Int J Rad Onc Biol Phys 2014; 90(2):312-319 OC-1030 Salvage LDR Prostate Brachytherapy: Results of NRG/RTOG-0526 Trial for Local Recurrence after EBRT J. Crook 1 , J. Rodgers 2 , T. Pisansky 3 , E. Trabulsi 4 , M. Amin 5 , W. Bice 6 , G. Morton 7 , N. Pervez 8 , E. Vigneault 9 , C. Catton 10 , J. Michalski 11 , M. Roach 12 , D. Beyer 13 , P. Rossi 14 , E. Horwitz 15 , V. Donavanik 16 , H. Sandler 17 1 BC Cancer Agency - Southern Interior, Radiation Oncology, Kelowna, Canada ; 2 NRG Oncology, Statistics and Data Management Centre, Philadelphoa, USA ; 3 Mayo Clinic, Radiation Oncology, Rochester, USA ; 4 Thomas Jefferson University Hospital, Urology, Philadelphia, USA ; 5 University of Tennessee Health Science Centre, Pathology, Memphis, USA ; 6 John Muir Health Systems, Radiation Oncology, Walnut Creek, USA ; 7 Sunnybrook Health Sciences Centre- Odette Cancer Centre, Radiation Oncology, Toronto, Canada ; 8 Cross Cancer Institute, Radiation Oncology, Edmonton, Canada ; 9 Centre Hospitalier Universitaire de Quebec, Radiation Oncology, Quebec, Canada ; 10 Princess Margaret Cancer Centre- University Health Network, Radiation Oncology, Toronto, Canada ; 11 Washington University School of Medicine, Radiation Oncology, St Louis, USA ; 12 Helen Diller Family Comprehensive Cancer Center- University of California, Radiation Oncology, San Francisco, USA ; 13 Cancer Centers of Northern Arizona, Radiation Oncology, Sedona, USA ; 14 Valley View Hospital Cancer Centre- Emory University, Radiation Oncology, Atlanta, USA ; 15 Fox Chase Cancer Center, Radiation Oncology, Philadelphia, USA ; 16 Helen F Graham Cancer Center- Christiana Care, Radiation Oncology, Newark, USA ; 17 Cedar Sinai, Radiation Oncology, Los Angeles, USA Purpose or Objective Prior studies of low dose rate (LDR) prostate brachytherapy (BT) for salvage of local recurrence (LR) after external beam radiotherapy (EBRT) are limited by retrospective reporting. We report efficacy outcomes of a prospective Phase II trial (NCT00450411) of salvage LDR BT.

Material and Methods Eligible patients had low or intermediate risk prostate cancer prior to EBRT and biopsy-proven LR > 30 mos after EBRT, with PSA < 10 ng/mL and no regional or distant disease. Prescribed minimum target dose was 140 Gy with I-125, or 120 Gy with Pd-103. The primary endpoint, late GI/GU Adverse Events (AEs) occurring 9-24 mos after BT, CTCAE V3.0 Grade 3 or higher and attributed to BT has been reported at 14%. All eligible patients who received protocol treatment were followed for a minimum of 5 years and included in this analysis for secondary clinical outcomes. Disease-free (DFS), disease-specific survival (DSS), and overall survival (OS) were estimated using the Kaplan-Meier method with hazard ratios and 95% confidence intervals computed using Cox proportional hazards models. Local tumor progression (LF), distant failure (DF), and biochemical failure (BF) were estimated using nonparametric estimation of cumulative incidence accounting for competing risk events. Time to LF, DF and BF were modeled by cause-specific Cox proportional hazards regression and adjusted for T-stage, PSA, Gleason score, age and other factors as appropriate. Results From 05/11/2007 - 01/21/2014, 100 patients were registered from 20 centers, of which 92 were analyzable. Median follow up is 6.9 years (range: 0.3-11.2); median age 70 (IQR: 66-74). Initial Gleason score was 7 in 48% and PSA >10 ng/ml in 16%. Median dose of prior EBRT was 74 Gy (IQR: 70-76). Androgen deprivation was combined with salvage BT in 16%. Median interval from prior EBRT was 85 mos (IQR: 60-119). 10-year OS is 70% (95% CI: 58 -83). 19 patients died (5 PCa, 10 other, 4 unknown). 4 had LF (one biopsied). 10-year LF rate is 5% (95% CI:1-11). 14 patients had DF (10-year rate 19% (95% CI:10-29)). The 10-year BF rate is 46% (95% CI:34-57). DFS (includes death from any cause) is 61% at 5 years but falls to 33% at 10 years. None of the baseline characteristics, including % of ETV covered by 100% of the prescription dose and interval from EBRT to brachytherapy were significantly associated with OS, DFS, local, distant, or biochemical failure. Conclusion This is the first prospective multicenter trial to report outcomes of salvage LDR BT for post EBRT LF. We previously reported late grade 3 GU/GI adverse events as occurring in14%. We now report 5-year freedom from biochemical failure comparable to other salvage modalities (68%). Although further local LF is rare (5%), there is a continued toll of prostate cancer recurrence such that freedom from Biochemical Failure at 10 years is 54%. Support: This project was supported by grants U10CA180868 and U10CA180822 from the NCI. OC-1031 The radiosensitivity index predicts benefit from HDR brachytherapy in high-risk prostate cancer N. Thiruthaneeswaran 1,2 , B.A.S. Bibby 1 , R. Pereira 3 , E. More 1 , H. Denley 4 , A. Henry 5 , J. Wylie 6 , P. Hoskin 7 , R. Bristow 3,8 , A. Choudhury 1 , C. West 1 1 University of Manchester, Translational Biology, Manchester, United Kingdom ; 2 The University of Sydney, Sydney Medical School, Sydney, Australia ; 3 University of Manchester, Translational Oncogenomics, Manchester, United Kingdom ; 4 Manchester Royal Infirmary, Department of Cellular Pathology, Manchester, United Kingdom ; 5 Leeds Cancer Centre, Clinical Oncology, Leeds, United Kingdom ; 6 The Christie NHS Foundation Trust, Clinical Oncology, Manchester, United Kingdom ; 7 Mount Vernon Cancer Centre, Clinical Oncology, Northwood, United Kingdom ; 8 Manchester Cancer Research Centre, The Oglesby Cancer Research Building, Manchester, United Kingdom Purpose or Objective There is a decline in the use of brachytherapy boost for high-risk prostate cancer patients despite an accumulation