Reliability of ultrasound imaging of pelvic floor morphology and function among females who have undergone pelvic radiotherapy

Aims To investigate the intra- and inter-rater reliability of two-dimensional (2D) transperineal ultrasound imaging (USI) measures of bladder wall thickness (BWT), urethral length (UL), and parameters related to levator plate length (LP) and transient changes in LP during pelvic floor muscle (PFM) contraction, and on Valsalva in women who received radiation therapy (RT) for treatment of pelvic cancer. Methods Twenty women with a history of RT for the treatment of pelvic cancer were assessed independently by two raters on the same day. Five outcomes were assessed for reliability: BWT, UL, and LP at rest (LP-R), during a maximal voluntary contraction of the PFMs (LP-MVC), and during a maximal-effort Valsalva maneuver (LP-MVM). Reliability was determined using intra-class correlation coefficients (ICC) and Bland-Altman analyses. Measurement error was determined using standard error of the measurement (SEM) and minimal detectable difference. Results Intra-rater reliability was very good for LP-R, LP-MVC, LP-MVM, and UL (ICC: 0.97 [0.93-0.99], 0.95 [0.88-0.98], 0.84 [0.59-0.94], and 0.96 [0.89-0.98], respectively). Inter-rater reliability was very good for LP-R (ICC: 0.82 [0.55-0.93]), and good for LP-MVC, LP-MVM, and UL (ICC: 0.79 [0.46-0.92], 0.79 [0.49-0.92], and 0.75 [0.36-0.90], respectively). BWT had poor intra- and inter-rater reliability. The variability between measurements was the smallest for LP-R, LP-MVC, and UL for intra-rater assessments, and for LP-R and UL for inter-rater assessments. SEM values for intra-rater assessments were LP-R: 1.5 mm, LP-MVC: 1.84 mm, LP-MVM: 4.33 mm, and UL: 1.16 mm. Conclusions Although these results support the reliability of 2D-transperineal USI for the evaluation of UL and PFM parameters, they do not support its use for the assessment of BWT.