Po55

Purpose Dose escalation with brachytherapy in combination with external beam radiotherapy (EBRT) improves long-term biochemical control in intermediate- and high-risk localised prostate cancer, and high dose rate brachytherapy (HDR) as monotherapy has been shown to be safe and effective in treating localised prostate cancer. We compare long-term efficacy and toxicity data for patients with unfavourable-intermediate and high-risk disease treated with HDR brachytherapy as boost (HDR-B) and HDR brachytherapy as monotherapy (HDR-M) between 2007 and 2018 at a single institution. Materials and Methods Retrospective record review was performed for sequential patients treated with HDR for localised prostate cancer from 20th March 2007 to 31st July 2018 after Human Research Ethics Committee approval. Recurrence and toxicity data was derived from medical records or direct patient contact where appropriate. Primary outcome measures included biochemical progression-free survival (bPFS), as defined by Phoenix criteria and toxicity, graded according to CTCAE v4.0. Multivariate regression using Cox proportional hazards model was performed to determine hazard ratio for bPFS between HDR-M and HDR-B groups. Results 268 patients with unfavourable-intermediate or high risk disease were identified, with 233 and 35 patients receiving HDR-B and HDR-M respectively. The median follow-up was 7.6 years for HDR-B and 5.1 years for HDR-M. Of 7 patients who received HDR-M with high risk disease, 5 had prior pelvic irradiation. In the HDR-B group, the brachytherapy dose delivered was 20Gy in 2 fractions in 94% of patients, and EBRT dose received was 46Gy in 23 fractions in 89%. The HDR-M dose delivered was 27Gy in 2 fractions (54.3%), 33Gy in 3 fractions (28.6%) and 34.5Gy in 3 fractions (14.3%). ADT was used in 71% of HDR-B patients, 37% of HDR-M patients, and 66% overall, with 43% receiving 12 months or more. The bPFS was 85.6% ((95% confidence interval [CI] 79.6%-90.0%) at 5 years and 71.8% (95% CI 62.1%-79.4%) at 10 years for HDR-B, and 77.5% (95% CI 58.1%-88.7%) at 5 years and 53.3% (95% CI 26.2%-74.4%) at 10 years for HDR-M, with a multivariate hazard ratio of 2.10 (p=0.08). Significant predictors of biochemical failure were primary tumour stage, Gleason grade group, and ADT use, with hazard ratios of 1.3 (p=0.01), 1.4 (p=0.03) and 0.6 (p=0.02). At 5 and 10 years, overall survival was 94% and 87% for HDR-B and 96% and 69% for HDR-M. The crude urethral stricture rate was 15.9% (n=37, 95% CI 11.7%-21.2%) for HDR-B, 11.4% (n=4, 95% CI 4.2%-27.5%) for HDR-M and 15.3% (95% CI 11.4%-20.1%) overall, with 39 requiring intervention at a median time of 2.2 years. Of the four patients in HDR-M group experiencing stricture, two had prior pelvic irradiation as risk factors. The overall rate of stricture was 25% (95% CI 17.7%-33.5%) with a median follow-up of 11.5 years for patients treated before 2010, and 8% (95% CI 4.5%-13.5%) with a median follow-up of 5.9 years for those treated 2010 onwards, after ultrasound planning software and hardware updates were implemented, and change from single implantation procedure regimen to multiple implantations. The rate of any urinary leakage was 12.4% (95% CI 8.8%-17.4%) and 0%(95% CI 0%-8.6%) for HDR-B and HDR-M respectively, with 6% (95% CI 3.6%-9.9%) of HDR-B requiring pad use or intervention. The rate of symptomatic late proctitis was 9% (95% CI 5.9%-13.5%) in HDR-B and 0% (95%CI 0-8.6%) in HDR-M. No late grade 4 or above toxicities occurred. Conclusions HDR brachytherapy as boost with external beam radiotherapy has high long-term biochemical control rates for unfavourable-intermediate- to high-risk localised prostate cancer. Early data suggests encouraging biochemical control and no significant detriment with HDR brachytherapy as monotherapy in selected patients, with low rate of late urinary incontinence and symptomatic proctitis. Dose escalation with brachytherapy in combination with external beam radiotherapy (EBRT) improves long-term biochemical control in intermediate- and high-risk localised prostate cancer, and high dose rate brachytherapy (HDR) as monotherapy has been shown to be safe and effective in treating localised prostate cancer. We compare long-term efficacy and toxicity data for patients with unfavourable-intermediate and high-risk disease treated with HDR brachytherapy as boost (HDR-B) and HDR brachytherapy as monotherapy (HDR-M) between 2007 and 2018 at a single institution. Retrospective record review was performed for sequential patients treated with HDR for localised prostate cancer from 20th March 2007 to 31st July 2018 after Human Research Ethics Committee approval. Recurrence and toxicity data was derived from medical records or direct patient contact where appropriate. Primary outcome measures included biochemical progression-free survival (bPFS), as defined by Phoenix criteria and toxicity, graded according to CTCAE v4.0. Multivariate regression using Cox proportional hazards model was performed to determine hazard ratio for bPFS between HDR-M and HDR-B groups. 268 patients with unfavourable-intermediate or high risk disease were identified, with 233 and 35 patients receiving HDR-B and HDR-M respectively. The median follow-up was 7.6 years for HDR-B and 5.1 years for HDR-M. Of 7 patients who received HDR-M with high risk disease, 5 had prior pelvic irradiation. In the HDR-B group, the brachytherapy dose delivered was 20Gy in 2 fractions in 94% of patients, and EBRT dose received was 46Gy in 23 fractions in 89%. The HDR-M dose delivered was 27Gy in 2 fractions (54.3%), 33Gy in 3 fractions (28.6%) and 34.5Gy in 3 fractions (14.3%). ADT was used in 71% of HDR-B patients, 37% of HDR-M patients, and 66% overall, with 43% receiving 12 months or more. The bPFS was 85.6% ((95% confidence interval [CI] 79.6%-90.0%) at 5 years and 71.8% (95% CI 62.1%-79.4%) at 10 years for HDR-B, and 77.5% (95% CI 58.1%-88.7%) at 5 years and 53.3% (95% CI 26.2%-74.4%) at 10 years for HDR-M, with a multivariate hazard ratio of 2.10 (p=0.08). Significant predictors of biochemical failure were primary tumour stage, Gleason grade group, and ADT use, with hazard ratios of 1.3 (p=0.01), 1.4 (p=0.03) and 0.6 (p=0.02). At 5 and 10 years, overall survival was 94% and 87% for HDR-B and 96% and 69% for HDR-M. The crude urethral stricture rate was 15.9% (n=37, 95% CI 11.7%-21.2%) for HDR-B, 11.4% (n=4, 95% CI 4.2%-27.5%) for HDR-M and 15.3% (95% CI 11.4%-20.1%) overall, with 39 requiring intervention at a median time of 2.2 years. Of the four patients in HDR-M group experiencing stricture, two had prior pelvic irradiation as risk factors. The overall rate of stricture was 25% (95% CI 17.7%-33.5%) with a median follow-up of 11.5 years for patients treated before 2010, and 8% (95% CI 4.5%-13.5%) with a median follow-up of 5.9 years for those treated 2010 onwards, after ultrasound planning software and hardware updates were implemented, and change from single implantation procedure regimen to multiple implantations. The rate of any urinary leakage was 12.4% (95% CI 8.8%-17.4%) and 0%(95% CI 0%-8.6%) for HDR-B and HDR-M respectively, with 6% (95% CI 3.6%-9.9%) of HDR-B requiring pad use or intervention. The rate of symptomatic late proctitis was 9% (95% CI 5.9%-13.5%) in HDR-B and 0% (95%CI 0-8.6%) in HDR-M. No late grade 4 or above toxicities occurred. HDR brachytherapy as boost with external beam radiotherapy has high long-term biochemical control rates for unfavourable-intermediate- to high-risk localised prostate cancer. Early data suggests encouraging biochemical control and no significant detriment with HDR brachytherapy as monotherapy in selected patients, with low rate of late urinary incontinence and symptomatic proctitis.