Patients and Methods:
Between June 2017 and February 2019, patients with localized prostate cancer who underwent RS-RARP by the same surgeon (Dr. HG) at Nanjing Drum Tower Hospital were reviewed retrospectively. All Patients underwent multiparameter prostate MRI to evaluate extraprostatic extension and seminal vesicle invasion. Preoperative bone scan was applied to exclude the metastatic bone disease. Patients staged as locally advanced or advanced prostate cancer at preoperative diagnosis were excluded. Patients who had received neoadjuvant hormonal therapy or transurethral resection of the prostate were also excluded. Furthermore, patients with preoperative urinary incontinence were also excluded.
First, we calculated median values of each MRI parameter. According to median values of each MRI parameter, patients were divided into 2 groups. Differences in patient characteristics such as age, prostate volume, prostate-specific antigen (PSA), body mass index (BMI), preoperative international prostate symptom score (IPSS), nerve preservation, D’Amico risk group10, biopsy gleason score, positive surgical margin, extracapsular extension, seminal vesicle invasion and immediate urinary continence after RS-RARP between groups dichotomized by median values for each MRI parameter were analyzed. Next, univariable and multivariate analysis were performed to identify predictors associated with immediate urinary continence, including several factors likely to be related to postoperative immediate urinary continence, such as prostate volume, nerve preservation, preoperative IPSS, age, and BMI, and MRI parameters.
Surgery and follow-up
The technique of RS-RARP we used was similar to the transperitoneal approach described by Galfano et al4, 11and Lim et al12. In patients with low risk prostate cancer, bilateral nerve were preserved, while those who did not meet the item did not retain the nerve. For patients at high risk of prostate cancer, extended lymph node dissection was performed. The catheter was removed between 7 and 10 days after operation, and discharged from hospital 3 to 5 days after operation. All patients were interviewed in the outpatient department every 3 month during the first year following RS-RARP to complete the questionnaire regarding urinary function or by telephone in case of missing questionnaires.
MRI Measurements and Imaging
The examinations were performed with a 3.0-T MR scanner (Ingenia, Philips Medical Systems, Best, the Netherlands). Patients were examined in the supine position. A 16- channel phased array surface body coil was used. Coronal T2-weighted images were obtained with the following parameters: repetition time (TR), 4050 ms; echo time (TE), 90 ms; slice thickness, 4 mm; intersection gap, 0.4 mm; field of view, 240 × 240 mm; matrix, 368 × 285. Sagittal T2-weighted imaging was performed with the following parameters: TR, 4050 ms; TE, 90 ms; slice thickness, 4 mm; intersection gap, 0.4 mm; field of view, 180 × 180 mm; matrix, 276 × 179. Transected T2-weighted images were obtained with the following parameters: TR, 4750 ms; TE, 80 ms; slice thickness, 3.5 mm; intersection gap, 1mm; field of view, 220 × 300 mm; matrix, 276 × 226.
The sagittal T2-weighted FSE sequences allowed for minimal residual membranous urethral length (mRUL) to be measured parallel to the membranous urethra from the inferior edge of the levator ani muscle to the superior margin of the bulbospongiosus muscle13 (Figure 1 A). Coronal T2-weighted sequences were used to measure peri-urethral sphincter complex (PSC) thickness, the thicknesses of the levator ani muscle (LAM), and obturator internus muscle (OIM) (Figure 1 B). We measured PSC from the urethral midline to lateral margin of the converging levator ani muscle. We measured LAM from the extreme length converging on the urethra immediately caudal to the apex of prostate. And we measured OIM in its wider part. We measured membranous urethra in its wider part in the transected T2-weighted sequences before entering in the prostate and defined it as urethral wall thickness (UWT)14 (Figure. 1 C). Measurements of the above MRI parameters were taken in a blind manner. All data were collected in centimeters with two decimal places.
We were used the Expanded Prostate Cancer Index Composite (EPIC) instrument to evaluated urinary continence15. All patients were considered as continence when they used no small safety liner or no pad at all. Immediate continence was defined as patients reported freedom from using any pad within 7 days after the urinary catheter was removed 6. All patients were subsequently reviewed within 7 days after the urinary catheter was removed to evaluate their urinary continence by accomplishing the self-administered questionnaire.
The Mann-Whitney U test was used for continuous data, and the chi-squared test or fisher exact test was used for categorical date. Continuous nonnormally distributed variables were presented as the median and interquartile range (IQR). Logistic regression analysis was applied for univariable and multivariable analysis to identify predictors of immediate urinary continence. All data analyses were performed using SPSS 21.0 statistical software (IBM SPSS, Chicago, IL, USA). A confidence interval (CI) of 95 % was assumed, and a P value <0.05 was considered significant.