Can MRI Findings Help Predict Toxicity After Radiotherapy for Prostate Cancer?

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.

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.”

(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.