Background
BPH is a histological diagnosis defined as an increased number of epithelial and stromal cells in the prostate. It is common in men over the age of 40, and the incidence increases with age. In the United States, 8 million men older than 50 years old suffer from BPH. Many cases are asymptomatic, however, symptoms may occur with prostate enlargement and compression of the urethra leading to bothersome lower urinary tract symptoms (LUTS), including voiding symptoms such as (hesitancy, weak stream, straining, prolonged voiding), and storage symptoms (frequency, urgency, and nocturia). Serious consequences can develop, including acute urinary retention, recurrent urinary tract infections, bladder stones and diverticula, hematuria, and renal insufficiency (1). The condition impacts quality of life (QOL) and is a substantial economic burden with a US estimated annual expenditure over 4 billion dollars (2).
Treatment for BPH varies based on symptom severity and ranges from conservative management (monitoring, lifestyle modifications), to medical management (alpha-blockers, 5-alpha-reductase inhibitors, antimuscarinic and beta-3 agonists), and finally surgical treatment in approximately 25% of men over 50 years old (3). Transurethral resection of the prostate (TURP) is considered the gold standard surgical intervention for BPH secondary to small to medium size prostates (30-80 cc). Interest in alternative surgical options arises from the complications associated with TURP, including dilutional hyponatremia (TUP syndrome), sexual dysfunction (erectile dysfunction (6.5%), anejaculation (>5%), retrograde ejaculation (53-75%)), infection, urethral strictures, bladder neck stenosis or contracture, and hematuria (1,4,5). The most common surgical procedure for large prostates (> 80 cc) is simple prostatectomy, which is effective with a low re-operation rate, but requires an abdominal approach and has a higher risk of bleeding, longer hospital stay (5 days), and catheterization times. Laser enucleation with holium (HoLEP) or thulium (ThuLEP) laser is an option for large prostates and offers shorter hospital stay and less bleeding, but is technically challenging with limited use in the United States (8,14).
In recent years, an alphabet soup of minimally invasive treatment options have emerged with the main goal to be equally effective to TURP, but with a more favorable safety and convenience profile. Ideally, this includes the rapid and durable relief of LUTS without compromise of sexual function, under local anesthesia in an ambulatory setting, with a short convalescence (9). Increasingly, a balance between symptomatic improvement in LUTS and preservation of sexual function is expected (10).
The only FDA cleared (De Novo classification for the resection and removal of prostate tissue for the treatment of LUTS resulting from BPH) Fluid Jet System, is the AquaBeam System (PROCEPT BioRobotics) (25). This transurethral approach uses a high-velocity saline jet and real-time ultrasound imaging with robotic assistance for targeted removal of prostate parenchyma while ideally sparing collagenous structures (blood vessels, surgical capsule, bladder neck). Pre-treatment, transrectal ultrasound (TRUS) maps out the specific region of the prostate to be resected while limiting resection in key anatomical areas (bladder neck, vermontanum, ejaculatory ducts, external urinary sphincter). Although resection limits are automatically computer generated, the surgeon ultimately defines the area of treatment, and the resection is then executed automatically via a robotic arm. After completion, flushed tissue particles can be sent for histological analysis; hemostasis is achieved using electro-cautery or traction from a 3-way catheter balloon. By minimizing conductive heat damage to erective nerves, Aquablation has a theoretical advantage in preserving sexual function. Operative time is reportedly short (mean 33 minutes) (2,11), and trials of novice users report a short learning curve (12,13). Surgeons rate the procedure to be of similar to less work than TURP or other open/robotic-assisted procedures (14).
Primary Evidence
Initial clinical experience was reported in 2016, and the technology obtained FDA clearance in 2017 after the publication of the WATER trial, a PHASE III multicenter international, double-blind, randomized, non-inferiority study with 181 subjects comparing Aquablation (116/181) to TURP (65/181) (11,15). Men 45-80 years old with prostate size 30-80 cc (by TRUS), moderate-severe LUTS (International Prostate Symptom Score (IPSS) ≥ 12), and maximum urinary flow rate (Qmax) <15ml/s were included and stringent exclusion criteria applied. After randomization, although treatment was by an unblinded research team, a separate blinded team performed all follow-up. The primary endpoint was the change in the IPSS at six months; scores decreased by 16.9 points and 15.1 points for Aquablation and TURP, respectively (noninferiority p<.0001 and superiority p=0.1347). The primary safety endpoint was the proportion of subjects with adverse events, defined as Clavien-Dindo grade 2 or higher or any grade 1 with persistent disability. The 3-month primary safety endpoint rate was lower in the Aquablation group than in the TURP group (26% vs 42%, p = 0.0149). The rate of persistent grade 1 events was lower after Aquablation (7% vs 25%, p = 0.0004), while the rate of grade 2 and greater events was similar (20% for Aquablation, 23% for TURP (p = 0.3038)). Safety results remained consistent at 6 months.
At two years, IPSS score improvement was sustained (14.7 in Aquablation and 14.9 in TURP (p=0.834, 95% CI for difference -2.1 to 2.6)), and Qmax improvement was large in both groups (11.2 and 8.6 cc/s for Aquablation and TURP, respectively (p = 0.1880, 95% CI for difference -1.3 to 6.4) (16). Two-year reduction in post-void residual (PVR) was 57 and 70 cc for Aquablation and TURP, respectively (p = 0.3895). Prostate specific antigen (PSA) decreased significantly in both groups by 1 point (p < 0.01). Retreatment rates were 4.3% and 1.5% (p = 0.42) in the Aquablation and TURP groups, respectively. Among the subset of sexually active men without the condition at baseline, anejaculation was less common after Aquablation (10% vs. 36%, p=0.0003). When post-Aquablation cautery was avoided rates of anejaculation were lower (7% vs. 16%, p=0.1774), and this resulted in the reduced grade 1 persistent events found in the Aquablation group. The authors hypothesize that Aquablation avoids damage to tissues involved in ejaculation though precise, image-based targeting, and robotic execution. Limitations of the study include the risk of performance bias as surgeons were not blinded, and unknown generalizability to a broader population.
WATER II was a prospective, uncontrolled, multi-centered international clinical trial to determine if the Aquablation technique was safe in men with large prostates (80-150 cc) (7,17). The mean prostate size was 107mL (range 80-150cc) with a middle lobe in 83%. Mean operative time was 37 minutes, mean resection time 8 minutes, and average length of hospital stay 1.6 days. Functional outcomes such as IPSS and Qmax, were similar to those seen in the WATER study. The primary safety endpoint, defined as CD Grade 2 or higher or any Grade 1 event resulting in persistent disability (e.g., ejaculatory disorder, erectile dysfunction, or permanent incontinence), at 3 months occurred in 45.5%, which met the study design goal of less than 65% (P <0.0001). Ejaculatory dysfunction occurred in 19% of sexually active men. While no electrocautery was used at time of surgery, 10 patients required transfusion and five cryptoscopic fulgurations for delayed bleeding. Severe hemorrhage rate for open simple prostatectomy is reported from 7-29%, but lower for alternative laser procedures (5). Complication rates are higher for larger prostates as they are typically more vascular and difficult to treat and the presence of middle lobe also makes this technically more difficult. The authors conclude: “while the outcomes are promising, longer follow-up will be necessary to confirm these results.”
A 2019 prospective, single-center, cohort study conducted in Germany evaluated the applicability of Aquablation to a non-selected patient collective (27). 118 consecutive patients with symptomatic BPH were enrolled and followed for 3 months post-procedure. Mean prostate volume at time of enrollment was 64.3 ± 32ml (range 20-154 ml); the number >80ml was not reported. Aquablation was successfully performed in all, with 10% experiencing significant bleeding requiring transfusion (2.5%) or second surgical intervention for bleeding (3.4%). IPSS, Qmax, and PVR improved significantly post procedure and out to 3 months.
A 2019 Cochrane Review based on 1-year WATER trial results, found evidence of parity with TURP to be of moderate-certainty related to the urologic symptom score (IPSS) primary outcome measure. All other metrics were graded low-certainty (QOL), to very low-certainly (adverse events, retreatments, erectile function, ejaculatory dysfunction) (1). Evidence was downgraded mainly due to study limitations (performance, reporting, and attrition bias), and imprecision (confidence intervals that crossed the assumed thresholds of clinically important differences or few events, or both). For example, both sexual outcome (erectile and ejaculatory function) results were downgraded two levels for a combination of imprecision and study limitations (high risk of performance and attrition bias). The authors recommend larger, more rigorously conducted, and transparently reported, studies comparing Aquablation to other techniques (laser enucleation, prostatic urethral lift, robotic-assisted simple prostatectomy) for which there is also increasing interest.
A 2019 systematic review reports on functional (IPSS, Qmax, QOL, PVR), sexual (erectile dysfunction, anejaculation), and safety outcomes (18). Nine studies were examined for a total of 445 patients screened. In addition to WATER I (1-year) and WATER II, a WATER I cohort analysis (19), pooled analysis on WATER I and II cohorts (20), and WATER II subpopulation analysis were included (21). The review reports improved outcomes in all functional outcome criteria for Aquablation, and statistical non-inferiority to TURP. In terms of safety, in the trials that compared Aquablation to TURP, outcomes (bleeding, urethral strictures, urinary retention, UTI, dysuria, bladder spasm, voiding dysfunction) were similar. Sexual outcomes, available in five papers, appear promising with International Index of Erectile function (IEEF-5) reduced as compared to TURP (33% vs. 56% in sub-analysis of WATER I, p=0.025). In two papers, there were no post-treatment erectile dysfunction (12,20), and one paper reported no difference from baseline (22). Ejaculation rates also show better maintenance after Aquablation, with lower rates of anejaculation, compared to TURP. In a population of 92 patients, no significant decrease in Male Sexual Health Questionnaire-Ejaculatory Dysfunction (MSHQ-EjD) at three months was reported (22). The review was limited by relatively small sample size and follow-up compared to other standard techniques, extreme heterogeneity in the description, and even reporting, of many outcomes (especially sexual), and lack of standardized validated questionnaires. The authors conclude that other multicenter randomized comparison trials (vs. TURP and laser therapy) with larger cohorts and longer follow-up are needed.
