A pilot study on dosimetric and radiomics analysis of urethral strictures following HDR brachytherapy as monotherapy for localized prostate cancer

Objectives: A cohort of HDR monotherapy patients was analysed to (i) establish the frequency of non-malignant urethral stricture; (ii) explore the relation between stricture formation with the dose distribution along the length of the urethra, and MRI radiomics features of the prostate gland. Methods: A retrospective review of treatment records of patients who received 19Gy single fraction of HDR BT was carried out. A matched pair analysis used one control for each stricture case matched with pre-treatment IPSS score, number of needles used and clinical target volume (CTV) volume for each stricture case identified. For all data sets, pre-treatment T2-weighted MRI images were used to define regions-of-interests along the urethra and within the whole prostate gland. MRI textural radiomics features - energy, contrast and homogeneity were selected. Wilcoxon signed-rank test was performed to investigate significant differences in dosimetric parameters and MRI radiomics feature values between cases and controls. Results: From Nov 2010 to July 2017, there were 178 patients treated with HDR BT delivering 19Gy in a single dose. With a median follow up of 28.2 months, a total of 5/178 (3%) strictures were identified. 10 patients were included in the matched pair analysis. The urethral dosimetric parameters investigated were not statistically different between cases and controls (p>0.05). With regards to MRI radiomics feature analysis, significant differences were found in contrast and homogeneity between cases and controls (p<0.05). However, this did not apply to the energy feature (p=0.28). Conclusions: In this matched pair analysis, no association between post-treatment stricture and urethral dosimetry was identified. Our study generated a preliminary clinical hypothesis suggesting that the MRI radiomics features of homogeneity and contrast of the prostate gland can potentially identify patients who develop strictures after HDR BT. Although the sample size is small, this warrants further validation in a larger patient cohort. Advances in knowledge: Urethral stricture has been reported as a specific late effect with prostate HDR brachytherapy. Our study reported a relatively low stricture rate of 3% and no association between post-treatment stricture and urethral dosimetry was identified. MRI radiomics features can potentially identify patients who are more prone to develop strictures.