BPPP: A novel pelvis-prostate model predicting immediate urinary continence after Retzius-sparing robotic-assisted laparoscopic radical prostatectomy

doi:10.21203/rs.3.rs-4266213/v1

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BPPP: A novel pelvis-prostate model predicting immediate urinary continence after Retzius-sparing robotic-assisted laparoscopic radical prostatectomy

https://doi.org/10.21203/rs.3.rs-4266213/v1

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published 20 Aug, 2024

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This study aimed to construct a novel pelvis-prostate model BPPP which consists of body mass index (BMI), prostate volume (PV), pelvic cavity index (PCI) and prostate-muscle index (PMI) to predict the immediate urinary continence after Retzius-sparing robot assisted laparoscopic radical prostatectomy (RS-RARP). The perioperative data of patients with prostate cancer who underwent RS-RARP in the department of urology of Nanjing Drum Tower Hospital from June 2018 to June 2022 were retrospectively analyzed. 280 patients were eligible for this study in total. Multivariate analysis showed that BMI, PV, PCI, PMI and NVB preservation were significantly associated with immediate urinary continence after RS-RARP. Subgroup analysis showed that patients with low BMI, low PV, high PCI and high PMI had a higher recovery rate of immediate urinary continence. The area under the curve of BPPP(BMI+PV+PCI+PMI) for predicting the immediate recovery of urinary continence after RS-RARP was 0.726. Delong test showed that the area under the curve of the combined test for predicting the immediate urinary continence after RS-RARP was better compared with single parameter (p<0.05). In conclusion the novel pelvis-prostate model BPPP may predict the immediate urinary continence after RS-RARP, providing information for preoperative decision‑making.

Biological sciences/Cancer/Cancer imaging

Biological sciences/Cancer/Cancer models

Biological sciences/Cancer/Urological cancer

Biological sciences/Cancer

Health sciences/Urology

Health sciences/Urology/Prostate

Prostate cancer (PCa) is the most common malignant tumor in the male urinary system. In the world, prostate cancer is the second most common male malignant tumor. The incidence and mortality of prostate cancer in the United States are the first and sixth among all male malignant tumors, respectively. ¹

Radical prostatectomy is the gold standard for the treatment of localized prostate cancer.² With the introduction of robot assisted laparoscopic system, the surgical procedure for prostate cancer is gradually transitioning to robot assisted radical prostatectomy (RARP).³ This operation has many advantages, such as three-dimensional magnification of the anatomical structure of the pelvis and prostate, the use of mechanical arm to improve the flexibility of operation, and the accuracy of suture and knot.⁴ However, the randomized controlled study conducted by Coughlin et al. compared the traditional open retropubic prostatectomy with robot assisted radical prostatectomy, showing that there was no significant difference in the recovery of postoperative urinary continence and erectile function 2 years after operation.⁵ In 2010, galfano team first carried out the Retzius-sparing robot assisted radical prostatectomy (RS-RARP) to complete the prostatectomy from the posterior approach through the rectovesical space.⁶ Compared with the traditional approach, this operation does not need to open the Retzius space, and protects the pelvic fascia, puboprostatic ligament, accessory pudendal artery, Santorini nerve and other structures, which are related to the recovery of urinary control and the preservation of sexual function. Through the posterior approach, complete intrafascial resection of the prostate can be achieved to protect the neurovascular bundle (NVB). The meta-analysis conducted by Rosenberg et al. showed that RS-RARP had advantages over RARP in immediate urinary continence after catheter removal. ⁷The randomized controlled single blind experiment conducted by the Department of Urology of Nanjing Drum Tower Hospital et al. also confirmed the above view⁸ (the immediate recovery ratio of urinary continence between RS-RARP group and RARP group was 69.1% vs 30.9%, RR 2.24,P = 0.000)

RS-RARP has some disadvantages, such as narrow operation space and increased operation difficulty and completing from below when anastomosing bladder and urethra. Different from the traditional operation, RS-RARP has a longer learning curve. RS-RARP is also more challenging for large volume prostate and middle lobe protruding prostate. Although RS-RARP has advantages in immediate urinary continence, there is no significant difference in long-term urinary continence and sexual function recovery compared with RARP. At the same time, due to the consideration of tumor control and positive surgical margin, there is no high-level clinical evidence to support the application of RS-RARP in the treatment of high-risk prostate cancer.⁹; ¹⁰

Previous studies have shown that high BMI, subcutaneous and abdominal pelvic fat accumulation, large prostate volume and narrow pelvic anatomy in obese patients will affect the operation space of radical prostatectomy.¹¹ From the perspective of surgical experience, fat rich visceral organs in obese patients often lead to narrow surgical field, limited operation space, difficulty in tissue structure identification and anatomy, and are more likely to damage surrounding structures and tissues related to urinary continence, such as urethral sphincter; The large volume prostate reduces the operation space of the pelvic cavity, and affects the process of anatomical separation of the tissue structure around the prostate, bladder and urethra anastomosis and reconstruction¹²; In the process of robot assisted laparoscopic surgery, the deep and narrow pelvic structure of patients will affect the accuracy of robot operation. The "difficult pelvis" has a relatively narrow operation space, and the pubic bone blocks the visual field. It is difficult to dissect the prostate apex and anastomose the urethra during the operation in the background of a difficult pelvis. Kaouk et al. ¹³first introduced the concept of pelvic cavity index (PCI) in single-port robot assisted laparoscopic radical prostatectomy. The larger pelvic cavity index represents the larger, wider and shallower pelvic space. It was found that PCI was positively correlated with the recovery of urinary continence 3 months after operation. Kimura et al. ¹⁴first introduced the concept of prostate-muscle index (PMI), the anatomical structure around the prostate, which can reflect the size of the pelvic cavity around the prostate, and found that it is related to the bleeding and the operation time during RARP. The above-mentioned pelvis- prostate model (BPPP) may further increase the operation difficulty of RS-RARP with narrow operation space, and further affect the goal of "three wins in a row" of radical prostatectomy (tumor control, urinary control and sexual control). Its impact on the greatest advantage of RS-RARP, that is, immediate urinary continence is not clear.

Based on the clinical research database of Urology in Nanjing Drum Tower Hospital and the follow-up Center for prostate cancer, this study retrospectively analyzed 280 patients with prostate cancer who underwent RS-RARP and were followed up after surgery by Nanjing Drum Tower Hospital.

By collecting the clinical, imaging and pathological data of patients during the perioperative period, combined with the recovery data of patients' urinary control in the follow-up center, the risk factors affecting the recovery of urinary control after RARP were explored. The predictive model was established and predictive value of pelvic-prostate model on the recovery of urinary continence after RARP was discussed; At the same time, we investigate the risk factors affecting the perioperative operation and pathological indicators (blood loss, operation time and positive margin) of RS-RARP, so as to provide a theoretical basis for the clinical preoperative prediction, operation decision-making, rehabilitation guidance and scientific research work.

Patients

421 patients with prostate cancer who underwent RS-RARP in the department of urology of Nanjing Drum Tower Hospital from June 2018 to June 2022 were retrospectively collected

Inclusion criteria:

(1) Prostate biopsy and postoperative pathology were confirmed as prostate cancer, and the preoperative Gleason score and postoperative pathological Gleason score were less than or equal to 8 points (including 3+3,3+4,4+3,4+4+3+5);

(2) The pelvis or prostate were examined by multi parameter magnetic resonance imaging before operation;

(3) The clinical baseline data and imaging data of the patients were evaluated by surgeon and an experienced radiologist. The tumor was localized, and the preoperative TMN staging was within T2C, without regional lymph node metastasis or distant metastasis; AJCC prognosis group was grouped in IIIA stage;

(4) Patients were generally in good condition, without serious underlying diseases, and could tolerate surgery;

(5) Patients were followed up by the prostate cancer postoperative follow-up center. The follow-up data were complete, and the follow-up time was ≥ 6 months.

Exclusion criteria:

(1) The preoperative imaging stage of patients was>T2C or recurrent and metastatic cancer;

(2) Patients had severe lower urinary tract symptoms before operation and had a history of catheter or previous TURP operation;

(3) Patients received hormone therapy or radiotherapy before operation;

(4) Patients had history of abdominal trauma or surgery;

(5) Patients were complicated with other malignant tumors;

(6) Patients were converted to open surgery or complicated with severe postoperative complications;

(7) Patients had delayed catheter removal (>14 days);

(8) The patients' clinical, imaging and pathological data were incomplete or the follow-up was lost;

(9) The compliance of postoperative functional training was poor, and the reliability of follow-up was low.

A total of 280 cases meeting the above inclusion and exclusion criteria were finally included.

We collected perioperative data of patients: age, body mass index (BMI), BMI=weight/height² (kg/m²), preoperative serum prostate specific antigen (PSA), prostate biopsy and postoperative pathological Gleason score, TNM staging (NCCN guideline 2022.4), AJCC prognosis group staging, intraoperative blood loss and console time, hospitalization time (total time from admission to discharge), positive surgical margin, NVB preservation during operation.

MRI imaging and Pelvimetry Measurements

Preoperative multi parameter MRI 3.0T prostate scan or pelvic scan measurement parameters (Figure1~4):

Prostate volume (PV): prostate width × length × height × (π/6);

Prostate apex depth (PAD): the vertical distance from the upper edge of the pubic symphysis to the apex of the prostate measured on sagittal T2WI images.

Pelvic inlet diameter (PID): the distance from the innermost edge of the superior border of pubic symphysis to the sacral promontory measured on sagittal T2WI images.

Pelvic depth (PD): the distance from the innermost edge of the inferior border of pubic symphysis to the sacral promontory measured on sagittal T2WI images.

Symphysis angle: the angle between the long axis of the pubic symphysis and the horizontal line measured on sagittal T2WI images.

Pelvic outlet diameter (POD): the distance between the tips of the ischial spines measured on axial T2WI image.

Pelvic cavity index (PCI): pelvic inlet diameter × pelvic outlet diameter/pelvic depth. PCI=PID×POD/PD.

Prostate muscle index (PMI): the sum of the distance between the inner edge of the obturator internus muscle and the lateral edge of the prostate measured on axial T2WI image showing the maximum width of the prostate.

Surgical techniques

The operation was completed by Da Vinci Xi (Intuitive surgical) operated by one senior doctor. The surgical method was RS-RARP, referring to the surgical methods reported by galfano et al. and lim et al. ⁶; ¹⁵

Postoperative follow-up data collection

According to the follow-up and telephone follow-up data of the prostate cancer follow-up center, the postoperative recovery of urinary continence and urinary incontinence were counted. The cut-off point of follow-up: immediate urinary continence after catheter removal (14 days after operation) and urinary continence 1 month, 3 months and 6 months after operation. Evaluation criteria for recovery of urinary continence: no need to use a urinary pad, or only one prophylactic urinary pad is needed every day, and the score of international incontinence consultation questionnaire short form (ICIQ-SF) is ≤ 2.

The study was approved by the Review Board of Afﬁliated Drum Tower Hospital, Medical School of Nanjing University (2017- 044-02) and was performed in accordance with the Declaration of Helsinki. We obtained written informed consent from each patient before surgery.

Statistical analyses

Imaging data statistics were checked by an imaging doctor and a urologist. Other clinical data and follow-up prognosis of patients were unknown at the time of statistics. All data were analyzed by SPSS 26.0 statistical software. For those continuous variables that conform to normal distribution or approximate normal distribution, they are expressed as mean ± standard deviation, and Student t test is used; The data of non normal distribution were expressed by median and quartile m (P25, p75), and the comparison between groups was performed by nonparametric test; The counting data are expressed in examples and percentages. The binary variables were expressed as percentages and analyzed by chi square test and Fisher exact test. Univariate logistic regression analysis was used to screen the risk factors significantly related to the recovery of urinary continence and operation related indicators, and the predictive efficacy of baseline data was obtained. The factors with P value less than 0.05 will enter the multivariate Logsitic regression analysis. Multivariate logistic regression was used to analyze the independent risk factors for the recovery of urinary continence after RS-RARP. Subsequently, we focused on the variables of interest and constructed a logistic regression prediction model, drew the ROC curve to determine the discrimination ability and the best critical value (determined by the maximum Youden index) of the relevant baseline data, and performed subgroup analysis. Binary logistic regression was used to calculate the predictive p value in the combined trial, and the best cutoff value and area under curve (AUC) of different parameters and the combined trial were obtained. Then, Delong test was used to compare the differences of several ROC curves. P<0.05 was statistically significant.

According to the inclusion criteria, a total of 421 patients with prostate cancer who underwent RS-RARP were collected. According to the exclusion criteria, a total of 280 patients finally entered the study. 141 patients were excluded, and some patients were excluded for a variety of reasons. 31 patients had severe lower urinary tract symptoms or had a history of catheter or previous TURP surgery. Three patients received neoadjuvant therapy before operation. 20 patients had a history of previous abdominal surgery or trauma. 12 patients were delayed in catheter removal. 87 patients had incomplete data or lost follow-up or poor compliance.

The age was 51-84 years old, with an average age of (69.0 ± 7.36) years; The preoperative PSA was 4.1-136.5 ng/ml, and the median preoperative PSA was 13.8 (7.6, 22.8) ng/ml; BMI ranged from 18.3 to 31.6 kg/m2, with an average BMI of (24.4 ± 2.97) kg/m2; The PV was 7.8-117.2ml, and the median PV was 37.2 (25.8, 52.6) ml; The Gleason score of prostate puncture was 6 in 60 cases (21.4%), 7 in 159 cases (56.8%), and 8 in 61 cases (21.8%); There were 7 cases (2.5%) in clinical T stage T1, 72 cases (25.7%) in T2a, 148 cases (52.8%) in T2b, and 53 cases (19.0%) in T2C; In AJCC prognosis group, there were 40 cases (14.3%) in stage I, 74 cases (26.4%) in stage IIA, 74 cases (26.4%) in stage IIB, 82 cases (29.3%) in stage IIC, and 10 cases (3.6%) in stage IIIA; The average pad was (3.3 ± 0.48) cm; The average PID was (11.5 ± 0.91) cm; The average pod was (8.7 ± 1.1) cm; The average PD was (12.7 ± 0.90) cm; PCI was 7.1-10.5cm, with an average of (8.52 ± 0.82) cm; The average PMI was (7.5 ± 0.6) mm; The average pubic symphysis angle was (34.1 ± 5.40) °; The average amount of bleeding was (273.4 ± 167.0) ml; The console time was 125-300 min, and the average console time was (166.8 ± 31.6) min; The average length of stay was (12.8 ± 5.6) days; There were 10 cases (3.6%) without NVB preservation, 167 cases (59.6%) with unilateral NVB preservation, and 103 cases (36.8%) with bilateral NVB preservation; 14 cases (5.0%) had positive resection margin after operation; The postoperative Gleason score was 6 in 42 cases (15.0%), 7 in 173 cases (61.3%), and 8 in 65 cases (23.2%); There were 182 cases (65.0%) with immediate recovery of urinary continence, 200 cases (71.4%) with recovery of urinary continence one month after operation, 221 cases (78.9%) with recovery of urinary continence three months after operation, and 257 cases (91.8%) with recovery of urinary continence six months after operation. (Table 1)

Risk factors and predictive value of immediate recovery of urinary continence after RS-RARP

In order to evaluate the predictive ability of variables for immediate recovery of urinary control, the data of perioperative patients were analyzed by univariate logistic regression. The results showed that the risk factors with statistical significance included age, BMI, prostate volume, PCI, PMI and NVB preservation (Table 2)

Since the results of univariate analysis would be affected by confounding factors, in order to correct this effect, the statistically significant indicators in Table 2 were taken as independent variables, and multivariate logistic regression analysis was conducted to further evaluate the predictive ability of these indicators for immediate recovery of urinary continece The results showed that BMI, PV, PCI, PMI and NVB preservation were independent risk factors for immediate recovery of urinary continence.(Table 3)

We used BMI, PV, PCI and PMI four parameters, and used logistic regression model to establish the combine test prediction probability logitp, so as to build the prediction model BPPP. ROC analysis showed that the AUC values of BMI, PV, PCI and PMI used alone to predict the immediate recovery of urinary continence in patients after RS-RARP were 0.601, 0.651, 0.595 and 0.556 respectively. In the single variable model, the AUC values of the four indicators were all lower than 0.7, with only moderate predictive value, and PV had the highest AUC value, which was the best predictive model for the immediate recovery of urinary continence after RS-RARP.

Considering the clinical practicability, the multivariate prediction model was obtained by the combine test of permutation and combination of four parameters. The AUC values of two parameter combined test (PCI+PMI), (PCI+PMI), (PCI+PV), (PMI+BMI), (PMI+PV) and (BMI+PV) were 0.641, 0.651, 0.685, 0.635, 0.664 and 0.681, respectively; The AUC values of three parameter combined test (PCI+PMI+BMI), (PCI+PMI+PV), (PCI+BMI+PV) and (PMI+BMI+PV) were 0.684, 0.702, 0.705 and 0.696, respectively; The AUC value of four parameter combined test (BPPP) was 0.726. The results show that the multi parameter prediction model can obtain better prediction value than the single parameter prediction model, and both of them have higher sensitivity and specificity. (Table 4, Figure 5)

According to the Delong test, there were significant differences between the four parameter combined test (BPPP) and each parameter separately. (Z values were -2.920, -2.593, -3.407, -4.061, respectively, P values were 0.003, 0.001, 0.001 and 0.001), which further proved that the multivariate prediction model was superior to the single variable prediction model. (Table 5)

BMI, PV, PCI and PMI were divided into two groups according to the best cut-off values of the four indicators obtained from the ROC curve. The immediate recovery rate of urinary continence after RS-RARP was analyzed in subgroups. The results showed that for BMI and PV, the rate of immediate recovery of continence after RS-RARP was higher in the group with values less than or equal to the optimal cut-off value than in the group with values greater than the optimal cut-off value; For PCI and PMI, the immediate recovery rate of urinary continence after RS-RARP with values greater than the optimal cutoff value was higher than that of RS-RARP with values less than or equal to the optimal cutoff value. The subgroup analysis showed that the lower the BMI and PV, the higher the PCI and PMI, the higher the immediate recovery rate of urinary continence after RS-RARP, which further verified the above statistical conclusion. (Table 6)

Risk factors of recovery of urinary continence at 1 month, 3 months and 6 months after RS-RARP

According to the univariate and multivariate analysis, PCI (or=1.194, p<0.001), PMI (or=1.123, p<0.001) and NVB preservation (or=4.520, p<0.001) were independent risk factors for the recovery of urinary contionence1 month after RS-RARP. (Table 7)

According to the univariate and multivariate analysis, PCI (or=1.159, p=0.02) and NVB preservation (or=3.471, p<0.001) were independent risk factors for the recovery of urinary continence 3 month after RS-RARP. (Table 8)

According to the univariate and multivariate analysis, NVB preservation (or=3.981, p<0.001) was an independent risk factor for the recovery of urinary continence 6 month after RS-RARP. (Table 9)

Risk factors of intraoperative blood loss and console time of RS-RARP

According to the univariate and multivariate analysis, PV (or=1.843, P=0.04) and PMI (or=0.953, P=0.001) were independent risk factors for intraoperative blood loss in RS-RARP (blood loss ≥ 250ml). (Table 10)

According to the univariate and multivariate analysis, BMI (or=1.633, P=0.02) and PCI (or=0.803, P=0.001) were independent risk factors for console time during RS-RARP (console time ≥ 160min). (Table 11)

Risk factors of positive pathological margin after RS-RARP

According to the univariate and multivariate analysis, the incidence of positive pathological margins in AJCC prognosis group with stage IIIA was higher than that in AJCC prognosis group with stage I-IIB (or=3.850, p<0.001), which was an independent risk factor for positive pathological margins after RS-RARP. (Table 12)

This study explored the risk factors of urinary continence, intraoperative blood loss, console time and postoperative pathological margin positive after RS-ARAP, and explored the predictive value of pelvis-prostate model BPPP for immediate urinary continence recovery in patients after RS-RARP.

In the past few decades, with the rise of economic level, the intensification of population aging and the popularity of PSA screening in physical examination, the incidence of prostate cancer in China has increased year by year. With the development of robot assisted laparoscopic technology, robot assisted radical prostatectomy (RARP) has gradually replaced the traditional open and laparoscopic surgery and become the preferred surgical method for the treatment of localized prostate cancer. The traditional RARP approach opens the retropubic space (Retzius space) and destroys the pelvic fascia, puboprostatic ligament, accessory pudendal artery and vascular nerve bundle, which are related to urinary control and erectile function.¹⁶ Galfnon returned to the anatomic structure, and through the posterior approach of the rectal-vesical space, took the lead in carrying out RS-RARP in order to improve the recovery of postoperative urinary continence and sexual function, and improve the postoperative quality of life.

After more than ten years of surgical accumulation, a large number of comparative studies have shown that the advantage of RS-RARP over the traditional retropubic approach is the early recovery of urinary continence. ¹⁷The characteristics of RS-RARP determine its narrow operation space, difficult anastomosis and prolonged learning curve. The anatomical structure of the pelvis can affect many aspects of the operation, such as the anatomical separation of apex of the prostate, bladder and urethra anastomosis, and further affect the early postoperative recovery of urinary continence.^18-20 Chen et al. found that the narrow and deep pelvic structure and low pelvic cavity index (PCI) of patients would have a negative impact on the fine operation of the manipulator during operation, regardless of the experience of the operator. ¹⁹

For patients with high BMI, pelvic fat accumulation often affects the surgical field and operation. A single center cohort study showed that BMI>30 can be used as an independent risk factor for urinary incontinence after laparoscopic radical prostatectomy.²¹ Large PV will affect the free anatomy of prostate and urethral reconstruction process during radical prostatectomy.²² For patients with large prostate volume undergoing laparoscopic radical prostatectomy, the recovery time of urinary continence is longer than that of patients with small prostate volume. ²³Some scholars have proposed the concept of prostate muscle index (PMI), which is defined as the sum of the distance between the inner edge of the obturator muscle on both sides and the outermost part of the prostate measured by the T2WI image with the largest width and diameter of the prostate. The obturator muscle will increase with the increase of BMI²⁴, reducing the pelvic space of the surgical field. Therefore, PMI can be used as an index to evaluate the size of the pelvic space around the prostate. ¹⁴For the above factors that may affect the operation space, such as BMI, PV, PCI and PMI, this study was set as pelvis-prostate model BPPP. We used the AUC value of ROC curve to judge the predictive value of these four parameters. It was found that PV had the highest predictive value in the single prediction model of pelvis-prostate model. The multivariate prediction model BPPP obtained higher AUC value than the single factor model through logistic regression. And through the Delong test, it is proved that the difference between the value of combine prediction and that of each individual parameter is statistically significant. Therefore, the combination of multiple pelvis- prostate parameters can improve the predictive ability of immediate urinary continence recovery after RS-RARP.

Post-prostatectomy incontinence is a complication of radical prostatectomy including RS-RARP. The mechanism is that the urethral reconstruction after radical prostatectomy shortens the functional urethral length, damaging the urethral sphincter, reducing the contractility, and the pressure in the urethra is lower than that in the bladder, resulting in involuntary urinary leakage and oozing.²⁵

The definition of urinary incontinence in this study is based on the use of urinary pads and the score of the international urinary incontinence counseling questionnaire. The follow-up is convenient and the patients' compliance is good. This study found that the recovery of urinary control after RS-RARP tended to improve with the increase of postoperative time (the recovery rates of urinary continence immediately after operation, 1 month, 3 months and 6 months after operation were 65.0%, 71.4%, 78.9% and 91.8%, respectively). NVB preservation was an independent risk factor throughout the cut-off point of postoperative urinary continence follow-up. The peripheral blood vessels and nerve bundles of the prostate generally ran on the posterolateral side of the prostatic capsule. The traditional radical prostatectomy was performed through extrafascial resection, along the levator ani fascia and the posterior approach of the prostatic fascia, which destroyed the NVB structure. However, RS-RARP method could be completely intrafascial resection to preserve NVB during operation. At present, there are improved VIP operation, super VIP operation and nonthermal intrafascial resection to protect NVB and improve the recovery rate of postoperative urinary continence. ²⁶; ²⁷

The prediction of blood loss and console time in RS-RARP plays an important role in the operation safety, perioperative nursing and reducing hospitalization costs.^28-30 Previous studies have shown that the extension of console time can reflect the difficulty of operation, and BMI, prostate weight, lymph node dissection and Gleason score can predict the extended operation time.³¹; ³² Uchida et al. found that preoperative BMI and prostate width can predict the operation time of RARP, so as to assess the operation risk and determine the appropriate RARP cases for novice surgeons.³³ Large volume prostate can cause more bleeding in the process of intraoperative prostate dissection, especially in patients with middle lobe hyperplasia of prostate, which protrudes into the bladder surface to increase the stripping area in the process of prostate separation and increase intraoperative bleeding. Multivariate regression analysis showed that PV and PMI were independent risk factors for surgical bleeding ≥ 250ml, while BMI and PCI were independent risk factors for console time ≥ 160min. The preoperative examination can predict the amount of bleeding and conseole time, and provide reference for perioperative nursing and preoperative decision-making. ADDIN

RS-RARP has no high-level evidence to support its application in patients with high-risk prostate cancer due to its concern about positive pathological margin and tumor biological recurrence.³⁴ Umari et al. ³⁵conducted a multicenter study to compare the postoperative oncological data of RARP and RS-RARP, and found that there was no significant difference in the postoperative positive rate of resection margin. (13.9% in RARP group vs. 15.6% in RS-RARP group, P=0.6). Galfano et al.³⁶ believed that the positive surgical margin after RS-RARP was only related to the surgeon's surgical decision and experience. Considering the improvement of patients' postoperative function, closer to the prostate in the process of surgical separation of the prostate will bring greater risk of positive surgical margin. Preoperative three-dimensional reconstruction of multi parameter MRI and artificial intelligence system can help surgeons make preoperative decisions to choose the anatomical range and how close to the prostate, so as to achieve a balance between postoperative functional recovery and the risk of positive margin. The positive rate of postoperative margin in the patients included in this study was 5.0%, which was less than the previous literature data. The positive rate of postoperative margin in the AJCC prognosis group with stage IIIA was higher than that in the AJCC prognosis group with stage I~IIC. It was considered that the included patients' lesions were limited to the prostate, early stage (≤ T2C), good prognosis (AJCC group with stage ≤ IIIA), continuous accumulation of surgical experience of a single operator, and reasonable preoperative decision (whether to preserve NVB according to the location of the tumor). ADDIN

This study has some limitations. First of all, this study is a single center retrospective study with a small sample size and bias in the follow-up process. The results have certain limitations. More prospective studies and external validation are needed to further verify the conclusions of this study.

Secondly, this study mainly considered the impact of pelvis-prostate model on the immediate recovery of urinary continence after RS-RARP, and did not include the impact of other anatomical markers or surgical intervention, such as the length of membranous urethra and clinical medication. During the follow-up process, the definition standard of urinary continence recovery was relatively simple, and the experimental methods such as urine pad weighing and urinary incontinence grading were not used, which had higher follow-up compliance but more accurate results. These may improve the model of this study. This case review study did not involve the study of patients' sexual control - erectile function, and lacked the exploration of postoperative quality of life for patients with sexual life requirements. Finally, this case-control study did not take into account the cumulative impact of doctors' surgical experience.

In the follow-up of this study, multi center prospective studies can be carried out, and more cases and different types of variables can be included to optimize the prediction model.

Pelvis-prostate model BPPP can predict the immediate recovery of urinary continence after RS-RARP. The predictive value of combined detection of four parameters is better than that of independent detection of each parameter. The patients with low BMI, low PV, high PCI, high PMI and NVB preserved during operation had a higher rate of immediate recovery of urinary continence after operation. The recovery rate of urinary continence showed an improvement trend with the extension of postoperative time. The patients with high PCI, high PMI and NVB preseravtion had a higher recovery rate of urinary continence at 1 month after operation; The patients with high PCI and NVB preservation had a higher recovery rate of urinary continence 3 months after operation; Patients with NVB preservation during the operation had a higher recovery rate of urinary continence 6 months after operation. The patients with high PV and low PMI had more intraoperative blood loss; Patients with high BMI and low PCI had more console time. The positive pathological margin was related to AJCC stage, and the higher the stage, the higher the positive rate. The conclusions of this study need to be verified by further multicenter prospective studies.

The authors declare they have no conflicts of interest.

Data availability and Author contributions

The datasets generated and analysed during the current study are not publicly available since ongoing clinical studies based on the same database are on progress but are available from the corresponding author on reasonable request.

Gutian Z, Xiaohu Z, Qing Z: conception and design. Hao W, Tianyi C: acquisition of data. Xiaohu Z, Qing: data analysis. Xiaohu Z: drafting of the manuscript. Hongqian G: critical revision of the manuscript. Xiaohu Z, Qing Z: statistical analysis. Hongqian G, Gutian Z: obtaining funding. Gutian Z: supervision.

Funding: The Sino-German Mobility Programme(M-0670), the Natural Science Foundation of Jiangsu Province (BE2020622)

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Table 1. Perioperative data of patients

Patient data parameters	value
Age (years)	69.0±7.36
Preoperative PSA (ng/ml)	13.8（7.6, 22.8）
BMI (kg/m2	24.4±2.97
PV（ml）	37.2（25.8, 52.6）
Gleason score of prostate biopsy
6	60/280(21.4%)
7	159/280(56.8%)
8	61/280(21.8%)
Clinical T stage
T1	7/280(2.5%)
T2a	72/280(25.7%)
T2b	148/280(52.8%)
T2c	53/280(19.0%)
AJCC prognostic group staging
I	40/280(14.3%)
IIA	74/280(26.4%)
IIB	74/280(26.4%)
IIC	82/280(29.3%)
IIIA	10/280(3.6%)
PAD（cm）	3.3±0.48
PID（cm）	11.5±0.91
POD（cm）	8.7±1.1
PD（cm）	12.7±0.90
PCI（cm）	8.52±0.82
PMI（mm）	7.5±0.6
Pubic symphysis angle (°)	34.1±5.40
Intraoperative blood loss (ml)	273.4±167.
Console time (min)	166.8±31.6
Length of stay (days)	12.8±5.6
NVB preservation
No	10/280(3.6%)
Unilateral	167/280(59.6%)
Bilateral	103/280(36.8%)
Positive margin after operation	14/280(5.0%)
Postoperative gleasn score
6	42/280(15.0%)
7	173/280(61.3%)
8	65/280(23.2%)
Recovery of urinary continece
Immediate recovery of urinary continence	182/280(65.0%)
Recovery of urinary continece 1 month after operation	200/280(71.4%)
Recovery of urinary continence 3 months after operation	221/280(78.9%)
Recovery of urinary continence 6 months after operation	257/280(91.8%)

Table 2. Univariate logistic regression analysis of immediate recovery of urinary continence after RS-RARP

variable	β	OR（95% CI）	P value
Age	-0.013	0.987（0.950-0.996）	0.003*
Preoperative PSA	-0.112	0.894（0.570-1.390）	0.713
BMI	-0.065	0.937（0.838-0.989）	0.02*
PV	-0.017	0.983（0.960-0.996）	<0.001*
Gleason score of prostate biopsy
6	reference value	-	-
7	0.373	1.452（0.725-3.041）	0.287
8	0.698	2.010（0.951-4.231）	0.541
Clinical T stage
T1	reference value	-	-
T2a	-0.025	0.976（0.347-2.747）	0.963
T2b	0.456	1.577（0.871-3.241）	0.561
T2c	0.849	2.338（0.521-7.541）	0.271
AJCC prognostic group staging
I	reference value	-	-
IA	-0.009	0.991（0.983-1.024）	0.617
IIA	0.104	1.110（0.987-1.496）	0.876
IIB	0.015	1.015（0.543-1.098）	0.547
IIC	0.212	1.236（0.887-1.512）	0.751
IIIA	0.042	1.043（0.761-3.881）	0.546
PAD	-0.017	0.983（0.960-1.006）	0.144
PID	0.290	1.336（0.830-2.153）	0.233
POD	-0.141	0.869（0.400-1.890）	0.723
PD	0.350	1.418（0.724-2.780）	0.309
PCI	0.116	1.230（1.080-1.380）	<0.001*
PMI	0.015	1.015（1.009-1.022）	<0.001*
Pubic symphysis angle	0.198	1.020（0.785-1.032）	0.731
Intraoperative blood loss	0.046	1.047（0.923-1.069）	0.258
Console time	0.022	1.023（0.981-1.031）	0.466
Length of stay	0.079	1.082（1.045-1.120）	0.091
NVB preservation	1.618	5.041（2.031-9.05）	<0.001*
Positive margin after operation	0.767	2.153（0.541-8.676）	0.657
Postoperative gleasn score
6	reference value	-	-
7	0.771	2.162（0.028-9.166）	0.237
8	0.307	1.360（0.781-1.699）	0.875

OR：Odds ratio

* p<0.05

Table 3. Multivariate analysis of risk factors for predicting immediate recovery of urinary continence after RS-RARP

variable	β	OR（95% CI）	P value
Age	-0.043	0.957（0.881-0.983）	0.583
BMI	-0.083	0.920（0.638-0.994）	<0.001*
PV	-0.022	0.978（0.713-0.989）	<0.001*
PCI	0.285	1.330（1.010-1.650）	0.003*
PMI	0.086	1.090（1.004-1.334）	<0.001*
NVB preservation	1.773	5.890（4.217-7.570）	<0.001*

OR：Odds ratio

* p<0.05

Table 4. Analysis of predictive value of pelvis-prostate model (BMI, PV, PCI, PMI) and combined test on immediate recovery of urinary continecne after RS-RARP

model	Cut-off value	AUC value	95%CI	Sensitivity	Specificity
BMI	23.4	0.601	0.529-0.672	0.754	0.416
PV	35.8	0.651	0.586-0.723	0.665	0.562
PCI	8.15	0.595	0.525-0.665	0.832	0.213
PMI	8.1	0.556	0.486-0.627	0.340	0.823
PCI+PMI	-	0.641	0.572-0.710	0.632	0.588
PCI+BMI	-	0.651	0.584-0.717	0.812	0.672
PCI+PV	-	0.685	0.618-0.751	0.809	0.712
PMI+BMI	-	0.635	0.566-0.704	0.786	0.677
PMI+BV	-	0.664	0.597-0.732	0.751	0.528
BMI+PV	-	0.681	0.613-0.748	0.769	0.590
PCI+PMI+BMI	-	0.684	0.619-0.749	0.754	0.561
PCI+PMI+PV	-	0.702	0.637-0.768	0.823	0.721
PCI+BMI+PV	-	0.705	0.640-0.770	0.785	0.669
PMI+BMI+PV	-	0.696	0.630-0.762	0.812	0.774
PCI+PMI+BMI+PV	-	0.726	0.663-0.789	0.796	0.690

Table 5. Delong test comparing different ROC curves

Comparison	Z value	P value
BMI~ PCI+PMI+BMI+PV	-2.920	0.003*
PV~ PCI+PMI+BMI+PV	-2.593	0.001*
PCI~PCI+PMI+BMI+PV	-3.407	0.001*
PMI~ PCI+PMI+BMI+PV	-4.061	0.001*

OR：Odds ratio

* p<0.05

Table 6. Subgroup analysis of immediate recovery of urinary continence after RS-RARP

Index	Number of cases	Immediate recovery rate of urinary continence	P value
BMI>23.4 kg/m2	157	57.0%	<0.001*
BMI≤23.4 kg/m2	123	75.2%
PV>35.8ml	165	62.1%	<0.001*
PV≤35.8ml	115	69.3%
PCI>8.15cm	177	70.4%	<0.001*
PCI≤8.15cm	103	55.7%
PMI>8.1mm	183	68.8	<0.001*
PMI≤8.1mm	97	57.8%

OR：Odds ratio

* p<0.05

Table 7. Univariate and multivariate analysis of urinary continence recovery 1 month after RS-RARP

Variable	Univariate analysis		Multivariate analysis
Variable	OR （95% CI）	P value	OR (95% CI)	P value
Age	1.520（0.916-1.827）	0.521
Preoperative PSA	0.998 （0.791-1.203）	0.289
BMI	0.985 （0.775-3.195）	0.090
PV	0.879 （0.734-2.024）	0.210
Gleason score of prostate biopsy (≤ 7 vs. 8)	1.521 （0.756-1.973）	0.083
Clinical T stage (T1~T2b vs. T2c)	1.089 （0.833-1.385）	0.458
AJCC prognostic group staging (I-IIC vs. IIIA)	1.089 （0.833-2.345）	0.489
PAD	1.020 （0.868-5.192）	0.589
PID	2.073 （0.289-2.621）	0.095
POD	1.547 （0.262-1.892）	0.410
PD	1.235 （0.054-3.375）	0.471
PCI	1.128 （1.089-4.415）	<0.001*	1.194 （1.074-4.909）	<0.001*
PMI	1.098 （1.006-3.201）	<0.001*	1.123 （1.008-3.359）	<0.001*
Pubic symphysis angle	1.419 （0.641-5.897）	0.923
Intraoperative blood loss	0.871 （0.671-1.571）	0.151
Console time	0.978 （0.671-3.071）	0.249
Length of stay	0.780 （0.540-5.020）	0.565
NVB preservation	4.441 （3.516-5.85）	<0.001*	4.520 （3.644-6.029）	<0.001*
Positive margin after operation	0.769 （0.548-1.545）	0.820
Postoperative gleasn score (≤ 7 vs.8)	0.853 （0.683-1.158）	0.798

OR：Odds ratio

* p<0.05

Table 8. Univariate and multivariate analysis of urinary continence recovery at 3 months after RS-RARP

Variable	Univariate analysis		Multivariate analysis
Variable	OR (95% CI)	P value	OR (95% CI)	P value
Age	0.928（0.781-2.175）	0.436
Preoperative PSA	1.028 （0.792-1.224）	0.449
BMI	0.978 （0.747-3.209）	0.104
PV	1.235 （0.957-5.513）	0.228
Gleason score of prostate biopsy (≤ 7 vs. 8)	1.489 （1.111-7.867）	0.190
Clinical T stage (T1-T2b vs. T2C)	1.291 （0.970-1.664）	0.433
AJCC prognostic group staging (I-IIC vs. IIIA)	1.015 （0.823-1.507）	0.783
PAD	1.140 （0.846-2.434）	0.747
PID	1.761 （1.279-5.243）	0.131
POD	0.997 （0.787-3.207）	0.885
PD	1.346 （0.948-10.74）	0.651
PCI	1.103 （1.005-2.283）	<0.001*	1.159 （1.010-2.796）	0.02*
PMI	1.154 （0.924-1.984）	0.095
Pubic symphysis angle	1.280 （0.570-6.990）	0.937
Intraoperative blood loss	2.485 （0.828-3.142）	0.389
Console time	1.139 （0.881-1.987）	0.567
Length of stay	0.901 （0.443-2.359）	0.786
NVB preservation	3.045 （2.023-4.86）	<0.001*	3.471 （2.928-4.503）	<0.001*
Positive margin after operation	0.583 （0.335-1.125）	0.871
Postoperative gleasn score (≤ 7 vs. 8)	1.091 （0.868-1.388）	0.552

OR：Odds ratio

* p<0.05

Table 9. Univariate and multivariate analysis of recovery of urinary continence 6 months after RS-RARP

Variable	Univariate analysis		Multivariate analysis
Variable	OR (95% CI)	P value	OR (95% CI)	P value
Age	0.893（0.825-1.765）	0.091
Preoperative PSA	3.296 （0.061-3.885）	0.573
BMI	0.885 （0.566-1.229）	0.158
PV	2.219 （0.743-2.397）	0.447
Gleason score of prostate biopsy (≤ 7 vs.8)	1.592 （0.195-1.991）	0.538
Clinical T stage (T1-T2B vs. T2C)	2.021 （0.827-2.215）	0.781
AJCC prognostic group staging (I-IIC vs. IIIA)	1.195 （0.961-2.429）	0.890
PAD	2.038 （0.683-2.393）	0.956
PID	1.124 （0.897-7.351）	0.198
POD	0.912 （0.777-3.047）	0.793
PD	1.588 （0.191-5.985）	0.087
PCI	1.512 （0.215-4.809）	0.382
PMI	0.812 （0.448-2.176）	0.142		< <
Pubic symphysis angle	1.876 （0.986-5.766）	0.679
Intraoperative blood loss	0.683 （0.555-1.811）	0.108
Console time	1.891 （0.368-2.454）	0.097
Length of stay	0.898 （0.520-1.228）	0.752
NVB preservation	2.981 （2.730-4.232）	<0.001*	2.981 （2.730-4.232）	<0.001*
Positive margin after operation	0.886 （0.390-1.582）	0.871
Postoperative gleasn score (≤ 7 vs. 8)	1.067 （0.771-1.863）	0.782

OR：Odds ratio

* p<0.05

Table 10. Univariate and multivariate analysis of intraoperative blood loss (blood loss ≥ 250ml) in RS-RARP

Variable	Univariate analysis		Multivariate analysis
Variable	OR (95% CI)	P value	OR (95% CI)	P value
Age	0.885 （0.581-1.250）	0.727
Preoperative PSA	1.091 （0.745-1.651）	0.871
BMI	12.672 (0.671-135.421）	0.981
PV	1.721 （1.345-2.298）	0.005*	1.843 （1.291-2.407）	0.04*
Gleason score of prostate biopsy (≤ 7 vs. 8)	1.792 （0.225-2.051）	0.761
Clinical T stage (T1-T2B vs. T2C)	3.445 （0.541-17.102）	0.571
AJCC prognostic group staging (I-IIC vs. IIIA)	1.257 （0.682-3.022）	0.628
PAD	1.009 （0.891-1.281）	0.670
PID	1.501 （0.778-2.593）	0.883
POD	0.871 （0.253-3.081）	0.451
PD	1.987 （0.289-2.914）	0.617
PCI	2.344 （0.354-4.933）	0.721
PMI	0.978 （0.892-0.997）	0.001*	0.953 (0.856-0.990）	0.001*
Pubic symphysis angle	1.891 （0.732-2.716）	0.541
Console time	1.267 （0.414-3.123）	0.189
Length of stay	0.898 （0.520-1.276）	0.752
NVB preservation	3.592 （0.891-14.432）	0.524
Positive margin after operation	8.145 （0.778-20.053）	0.894
Postoperative gleasn score (≤ 7 vs. 8)	1.554 （0.790-1.891）	0.745

OR：Odds ratio

* p<0.05

Table 11. Univariate and multivariate analysis of console time (console time ≥ 160min) during RS-RARP

Variable	Univariate analysis		Multivariate analysis
Variable	OR (95% CI)	P value	OR (95% CI)	P value
Age	0.997 （0.681-2.015）	0.487
Preoperative PSA	1.771 （0.749-2.651）	0.931
BMI	1.651 （1.131-2.280）	0.009*	1.633 （1.002-2.653）	0.02*
PV	2.883 （0.781-5.961）	0.195
Gleason score of prostate biopsy (≤ 7 vs. 8)	1.520 （0.338-3.716）	0.197
Clinical T stage (T1-T2B vs. T2C)	4.310 （0.810-10.335）	0.871
AJCC prognostic group staging (I-IIC vs. IIIA)	1.998 （0.235-6.617）	0.622
PAD	1.098 （0.776-1.281）	0.080
PID	2.341 （0.983-5.982）	0.762
POD	0.886 （0.198-4.092）	0.288
PD	1.550 （0.789-3.342）	0.665
PCI	0.792 （0.589-0.987）	0.003*	0.803 （0.501-0.993）	0.001*
PMI	1.291 （0.876-2.328）	0.881
Pubic symphysis angle	2.889 （0.891-8.651）	0.871
Length of stay	2.473 （0.712-5.886）	0.892
NVB preservation	1.092 （0.761-1.345）	0.523
Positive margin after operation	3.462 （0.598-10.342）	0.871
Postoperative gleasn score (≤ 7 vs. 8)	1.487 （0.231-3.891）	0.761

OR：Odds ratio

* p<0.05

Table 12. Univariate and multivariate analysis of positive pathological margins after RS-RARP

Variable	Univariate analysis		Multivariate analysis
Variable	OR (95% CI)	P value	OR (95% CI)	P value
Age	0.876（0.289-1.205）	0.133
Preoperative PSA	2.58 （0.171-10.885）	0.523
BMI	0.776 （0.871-1.509）	0.289
PV	2.051 （0.799-4.381）	0.561
Gleason score of prostate biopsy (≤ 7 vs.8)	1.091 （0.871-2.953）	0.090
Clinical T stage (T1-T2B vs. T2C)	2.871 （0.125-8.715）	0.289
AJCC prognostic group staging (I-IIC vs. IIIA)	3.850 （2.781-4.990）	<0.001*	3.850 （2.781-4.990）	<0.001*
PAD	1.965 （0.883-2.190）	0.876
PID	4.347 （0.338-20.351）	0.278
POD	0.996 （0.719-2.017）	0.871
PD	2.233 （0.298-4.185）	0.792
PCI	1.399 （0.897-3.102）	0.316
PMI	0.985 （0.334-4.196）	0.289		< <
Pubic symphysis angle	2.548 （0.781-14.061）	0.775
Intraoperative blood loss	0.989 （0.104-7.825）	0.781
Console time	1.911 （0.389-17.651）	0.870
Length of stay	4.881 （0.761-25.221）	0.747
NVB preservation	1.998 （0.927-7.804）	0.089
Postoperative gleasn score (≤ 7 vs. 8)	1.298 （0.787-3.341）	0.612

OR：Odds ratio

* p<0.05

No competing interests reported.

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BPPP: A novel pelvis-prostate model predicting immediate urinary continence after Retzius-sparing robotic-assisted laparoscopic radical prostatectomy

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