For men treated for prostate cancer, post-radiation gastrointestinal toxicity, commonly in the form of urinary frequency/urgency, may be significantly more common for those identified as having a longer prostatic urethral length (PUL) on pre-treatment magnetic resonance imaging (MRI).
For the retrospective study, recently published in Academic Radiology, researchers reviewed data from pre-treatment prostate MRI exams conducted for 361 men (median age of 68) who had radiation treatment for prostate adenocarcinoma and documented findings of genitourinary (GU) toxicity. The radiation treatments performed in the study cohort included moderately high dose-rate (HDR) brachytherapy (33 percent), hypofractionated external beam radiation therapy (EBRT) (28.3 percent), stereotactic body radiotherapy (SBRT) (24.4 percent) and conventionally fractionated EBRT (14.1 percent). The median follow-up period for late toxicity was 15 months, according to the study.
The multivariable analysis indicated that longer PUL on pre-treatment MRI was the only factor associated with an increased risk of late toxicity after radiotherapy treatment. Specifically, the researchers found that the presence of a longer PUL on MRI had a 1.7 hazard ratio (HR) for late grade >2 GU toxicity, with urinary frequency/urgency being the most common result.
“ … Longer PUL was associated with an increased risk of developing late grade >2 urinary toxicity. This remained significant when accounting for multiple clinical and radiotherapy factors, including baseline urinary function and radiation treatment modality,” wrote study co-author Kiran R. Nandalur, M.D., who is affiliated with the Department of Radiology and Molecular Imaging at Corewell Health William Beaumont University Hospital in Royal Oak, Michigan, and colleagues.
Here one can see a 4.4 cm prostatic urethra (A) and 2.3 cm membranous urethra (B) on quantitative MRI images for a 63-year-old patient who had grade 2 retention after stereotactic body radiation therapy (SBRT). A sagittal MRI (C) in a 67-year-old patient without late toxicity symptoms revealed a 3.3 cm prostatic urethral length. (Images courtesy of Academic Radiology.)
The researchers emphasized that no significant links for post-radiation late GU toxicity were found for other clinical factors, or the different forms of radiation treatment utilized in the study cohort.
“These findings underscore that current models may be underdeveloped and additional anatomic factors, such as PUL, can potentially improve risk stratification models,” pointed out Nandalur and colleagues. “Furthermore, optimizing urethral sparing during radiation treatment planning may be increasingly important for patients with a longer PUL.”
Three Key Takeaways
- Longer prostatic urethral length (PUL) on pre-treatment MRI increases risk of genitourinary toxicity. The study suggests that in men treated for prostate cancer, a longer prostatic urethral length (PUL) identified on pre-treatment MRI is associated with a significantly higher risk of post-radiation genitourinary toxicity, particularly in the form of urinary frequency/urgency.
- PUL assessment for risk stratification. The findings indicate that PUL assessment can be a valuable factor in risk stratification for patients undergoing radiation treatment for prostate cancer. It is highlighted as a factor that can improve the accuracy of risk stratification models, and optimizing urethral sparing during radiation treatment planning may be important for patients with a longer PUL.
- Minimal impact on MRI evaluation time. The study authors note that assessing PUL should not significantly extend the evaluation time for prostate MRI interpretation. It can be easily measured manually or with the assistance of AI automated segmentation methods, as the metric is evaluable on routinely performed sagittal T2W images. This suggests that PUL assessment can be incorporated into standard MRI protocols without substantial time implications.
(Editor’s note: For related content, see “Multinational Study Suggests High Variability with Quality of Prostate MRI,” “Seven Takeaways from Recent Review on Prostate MRI Imaging Quality” and “Can a Deep Learning Algorithm Enhance Detection of Prostate Cancer Recurrence with Biparametric MRI?”)
The study authors added that PUL assessment should not add significant evaluation time for prostate MRI interpretation.
“Given the metric is evaluable on sagittal T2W images, which are routinely performed in many centers as part of PI-RADS v2.1, provision of the length would likely be of minimal extra time measured manually or with arising AI automated segmentation methods,” noted Nandalur and colleagues.
(Editor’s note: For related content on prostate cancer imaging, click here.)
Beyond the inherent limitations of a retrospective study, the authors acknowledged a short follow-up period and potential selection bias with the exclusion of patients who did not have MRI in a six-month period prior to completing radiotherapy for prostate adenocarcinoma. The researchers also noted the study did not assess the treatment of urinary symptoms prior to or after radiotherapy.