Longer prostatic urethra increases risk of AEs after prostate cancer radiation

Data published in Academic Radiology show that increased prostatic urethral length detected on MRI increases the risk of adverse events (AEs) following radiation therapy for prostate cancer.¹

“We believe this particular area is more exposed to the radiation doses patients receive, resulting in direct inflammation," says Kiran R. Nandalur, MD.

The investigators found that every 1-cm increase in prostatic urethral length was associated with a 60% increased likelihood of experiencing genitourinary (GU) toxicity post-treatment. Further, larger prostatic urethra was associated with an increased risk of late (greater than 180 days) GU toxicity (HR, 1.59; 95% CI, 1.17–2.04; P < .01) as well as an increased risk of grade 2 or greater AEs related to frequency and urgency (HR, 1.72; 95% CI, 1.29–2.29; P < .01). These findings remained even after accounting for factors such as urinary function at baseline and radiation treatment modality.

Further, patients were nearly twice as likely to develop urinary symptoms and urinary frequency when their prostatic urethra was greater than 4.6 cm in length.²

“We believe this particular area is more exposed to the radiation doses patients receive, resulting in direct inflammation. [Although] chronic moderate urinary [adverse] effects were more problematic in approximately 28% of participants after 3 years, the good news is less than 3% of men experienced severe urinary [adverse] effects,” said co-author Kiran R. Nandalur, MD, in a news release on the findings.² Nandalur is a radiologist at Corewell Health in Royal Oak, Michigan.

A total of 361 men with prostate adenocarcinoma were included in the study. Each patient had undergone MRI within the prior 6 months before undergoing radiation therapy. The median age of participants was 68 years. Patients were excluded from the study if they had a history of previous prostate radiation, radical prostatectomy, transurethral resection of the prostate, and ablation or had a lack of clinical, radiotherapy, or follow-up data. Both prostatic urethral length and membranous urethral length (MUL) were measured.

The types of radiation treatment modalities were relatively balanced among participants, with 14.1% receiving conventionally fractionated external beam radiation (EBRT) alone, 28.3% receiving moderately hypofractionated EBRT alone, 33% receiving high dose rate (HDR) brachytherapy, and 24.4% receiving stereotactic body radiotherapy.

The investigators observed that HDR brachytherapy was associated with increased odds of acute (180 days or less) grade 2 or greater GU toxicity (odds ratio [OR], 2.9; 95% CI, 1.5–5.8; P < .01). Conversely, longer MUL was associated with decreased odds of acute GU toxicity (OR, 0.41; 95% CI, 0.18–0.92; P = .03).

Overall, acute grade 2 or greater AEs were experienced by 14.4% (50/347) of patients included in the study, with the most prevalent being increased urinary frequency or urgency, experienced in 10.7% of participants. Among all patients, 12 experienced more than 1 grade 2 or greater AE. Grade 3 acute toxicity was experienced by 4 patients (1.2%), and there were no instances of grade 4 or 5 urinary toxicities.

About 88.7% and 72% of patients were free of late grade 2 or greater toxicity at 1 and 3 years, respectively, with median follow-up of 15 months.

Nandalur concluded in the news release,2 “Our novel MRI metric may help patients know beforehand what their risk is in developing these symptoms and help them make better and more informed decisions on a course of treatment that optimizes quality of life. Doctors also can look at ways to better spare the prostatic urethra area from radiation and potentially decrease the [adverse] effects.”

References

1. Lee J, Nandalur S, Hazy A, et al. Prostatic urethral length on MRI potentially predicts late genitourinary toxicity after prostate cancer radiation. Acad Radiol. Published online October 17, 2023. Accessed October 26, 2023. doi:10.1016/j.acra.2023.09.004

2. Simple MRI scan could predict radiation side effects for prostate cancer. News release. Corewell Health. October 18, 2023. Accessed October 26, 2023. https://www.newswise.com/articles/simple-mri-scan-could-predict-radiation-side-effects-for-prostate-cancer