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The incidence of acute and late GU morbidity was higher after LDR-PB boost, and there was a nonsignificant trend for worse GI morbidity. No differences in the frequency of erectile dysfunction were observed.

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Introduction: Isolated local recurrence of prostate cancer following primary radiotherapy or brachytherapy may be treated with focal salvage high dose rate brachytherapy, although there remains an absence of high quality evidence to support this approach. Methods: Men with prostate cancer treated consecutively between 2015 and 2018 using 19 Gy in a single fraction high dose rate brachytherapy (HDR) for locally recurrent prostate cancer were identified from an institutional database. Univariable analysis was performed to evaluate the relationship between patient, disease and treatment factors with biochemical progression free survival (bPFS). Results: 43 patients were eligible for evaluation. Median follow up duration was 26 months (range 1-60). Median bPFS was 35 months (95% confidence interval 25.6-44.4). Kaplan-Meier estimates for bPFS at 1, 2 and 3 years post salvage were 95.2%, 70.6% and 41.8% respectively. On univariable Cox regression analysis, only nadir PSA was significantly associated with bPFS although the majority of patients were also treated with androgen deprivation therapy. Only one late grade 3 genitourinary toxicity was observed. Conclusion: Focal salvage HDR brachytherapy may provide good biochemical control with a low risk of severe toxicity. Further evaluation within clinical trials are needed to establish its role in the management of locally recurrent prostate cancer.

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Low dose rate brachytherapy High dose rate brachytherapy External beam radiotherapy a b s t r a c t Introduction: There is evidence to support use of external beam radiotherapy (EBRT) in combination with both low dose rate brachytherapy (LDR-EBRT) and high dose rate brachytherapy (HDR-EBRT) to treat intermediate and high risk prostate cancer. Methods: Men with intermediate and high risk prostate cancer treated using LDR-EBRT (treated between 1996 and 2007) and HDR-EBRT (treated between 2007 and 2012) were identified from an institutional database. Multivariable analysis was performed to evaluate the relationship between patient, disease and treatment factors with biochemical progression free survival (bPFS).Results: 116 men were treated with LDR-EBRT and 171 were treated with HDR-EBRT. At 5 years, bPFS was estimated to be 90.5% for the LDR-EBRT cohort and 77.6% for the HDR-EBRT cohort. On multivariable analysis, patients treated with HDR-EBRT were more than twice as likely to experience biochemical progression compared with LDR-EBRT (HR 2.33, 95% CI 1.12-4.07). Patients with Gleason 8 disease were more than five times more likely to experience biochemical progression compared with Gleason 6 disease (HR 5.47, 95% CI 1.26-23.64). Cumulative incidence of grade 3 genitourinary and gastrointestinal toxicities for the LDR-EBRT and HDR-EBRT cohorts were 8% versus 4% and 5% versus 1% respectively, although these differences did not reach statistical significance. Conclusion: LDR-EBRT may provide more effective PSA control at 5 years compared with HDR-EBRT. Direct comparison of these treatments through randomised trials are recommended to investigate this hypothesis further.

Aims To examine the relationship between post-implant CT dosimetry and long term PSA relapse free survival in patients treated with Iodine 125 LDR prostate brachytherapy as monotherapy and secondly, to audit recent practice against RCR guidelines following the re-introduction of post-implant dosimetry for all patients in our centre. Similarly an increase in the mean (SD) V100 from 92 (4.4) % to 95 (3.2) % is noted over time. No difference between clinicians was noted. Henry et al. 3 Conclusion D90 values of less than 140Gy continue to be predictive of increased risk of recurrence of prostate cancer across risk groups with longer follow-up. Quality assurance can be used to ensure improved and consistent implant quality in a team with multiple clinicians. Methods and Materials

tumour cell densities. The iterative local search approach increases the TCP to a target value whilst constraining the dose to the urethra below user defined dose/volume constraints. Results: Co-registration of the in-vivo mp-MRI with ex-vivo MRI is challenging with considerable effort needed in image acquisition and post processing to obtain the accuracy required for focal planning (Fig 1). An ensemble-based supervised classification algorithm, trained on textural image features, demonstrates a highly sensitive method for automated tumour delineation in high resolution histology images (2). Colour deconvolution and the use of a radial symmetry transform provides measures of cell density, shown to highly correlate with expert pathologist markup of tumour location(3). Statistical methods including machine learning techniques available in R software and MATLAB have demonstrated the potential for parameter maps from mp-MRI, including ADC maps, Ktrans, and T2* to be correlated with tumour characteristics including tumour cell density, Gleason score and hypoxia. The biological inverse optimization algorithm demonstrated significant reduction in urethral doses compared with conventional treatment approaches whilst maintaining tumor control probility (TCP) with the degree of dose reduction depending on the specified planning objectives. These plans have demonstrated robustness in the presence of clinically realistic seed displacements. Conclusions: We present a novel approach to focal brachytherapy planning with a goal to maintain high tumour control rates with minimal toxicity.