MRI findings of radiation-induced changes in the urethra and periurethral tissues after treatment for prostate cancer

Abstract

PurposeTo assess radiotherapy (RT)-induced changes in the urethra and periurethral tissues after treatment for prostate cancer (PCa). Methods and materialsThis retrospective study included 108 men (median age, 64 years; range, 43–87 years) who received external-beam radiotherapy (EBRT) and/or brachytherapy for PCa and underwent endorectal-coil MRI of the prostate within 180 days before RT and a median of 20 months (range, 2–62 months) after RT. On all MRIs, two readers independently measured the urethral length (UL) and graded the margin definition (MD) of the urethral wall and the signal intensities (SIs) of the urethral wall and pelvic muscles on 4-point scales. ResultsThe mean urethral length decreased significantly from pre- to post-RT MRI (from 15.2 to 12.6mm and from 14.4 to 12.9mm for readers 1 and 2, respectively; both p-values <0.0001). Brachytherapy resulted in greater urethral shortening than EBRT. After RT, SI in the urethral wall increased in 57% (62/108) and 35% (38/108) of patients (readers 1 and 2, respectively). The frequency and magnitude of SI increase in pelvic muscles depended on muscle location. In the obturator internus muscle, SI increased more often after EBRT than after brachytherapy, while in the periurethral levator ani muscle SI increased more often after brachytherapy than after EBRT. ConclusionAfter RT for PCa, MRI shows urethral shortening and increased SI of the urethral wall and pelvic muscles in substantial percentages of patients.