Background: In recent years, endoscopic laser surgery has been introduced to the treatment of NMIBC. Various types of laser (holmium laser, thulium laser and green-light laser) have been examined in the treatment of NMIBC, and the cutting power has been raised gradually. In our previous study, a 120 W green-light laser was used to perform en bloc resection, which yielded encouraging results. Endoscopic submucosal dissection by the HybridKnife was reported to be safe and effective in the treatment of NMIBC. However, previous resection was performed by electrical instrument. To further enhance the safety and accuracy of the operation, surgeons improved the treatment by combining laser resection and endoscopic submucosal dissection (ESD). This novel surgical treatment can also integrate advantages of each method. A retrospective study was designed in this study. The aim of the study was to evaluate the safety and efficacy of this novel surgical treatment, high-power green-light laser endoscopic submucosal dissection (HPL-ESD), in the treatment of primary non-muscle-invasive bladder cancer (NMIBC).

Introduction: Greenlight lasers are developed from Nd:YAG laser. Visual laser vaporization with Nd:YAG laser was introduced for the treatment of bladder cancer in the early 1990s. However, the low-absorption in most tissues with a penetration depth of 4-18mm leading to a deep coagulative necrosis of tissue, which increased the risk of delayed bladder perforation and bowel injury. Passing the Nd:YAG-produced beam (1046nm) through a KTP or LBO crystal, leads to a green visible light beam of 532nm, which has a completely different laser beam-tissue interaction. The wavelength is not absorbed by water but strongly absorbed by hemoglobin, which limits the optical penetration depth of green light laser to 0.8 mm, and the heat remaining in the tissue induces a coagulation zone of only 1-2mm thickness. Recent studies show that greenlight laser vaporization is a reliable and feasible treatment for the patients with primary NMIBC compared with standard TURBT.

On the basis of our previous surgical procedure, we developed this new surgical method by introducing ESD technology. Thus LBO laser en bloc resection was combined with the ESD technique to treat NMIBC, which was inspired by waterjet-assisted ESD in the department of gastroenterology. ESD was developed from endoscopic mucosal resection (EMR) and widely applied for the treatment of early gastroesophageal cancer and colorectal neoplasms. The bladder wall shares a similar histological structure with the gastrointestinal tract, although the muscularis propria is thicker. Therefore, forming a submucosal fluid cushion in the bladder wall should be feasible and even safer. The effects of submucosal fluid cushion on bladder wall were showed intuitively. The interspace between the mucosal layer and the detrusor muscle layer was increased, and the tissue between the two layers was rendered looser. In the present study, the submucosal fluid cushion increases safety during the operation. More importantly, when the normal mucosa was incised, the detrusor muscle layer beneath was exposed, which facilitated distinction of which layer was reached and incision of the entire tumor with the superficial detrusor muscle beneath the basal part. To some extent, introduction of the ESD technique enabled safe, controllable and accurate incision.

Equipment: The equipment included a 23F continuous flow resectoscope through which a 6F green-light lithium triborate (LBO) laser fiber (Realton, Beijing, China) could be delivered via the working channel. In addition, a disposable injector was used to form the submucosal fluid cushion for ESD. The stainless steel needle of the injector is 5 mm in length and 0.6 mm in diameter (terminal part). The working length and diameter are 1650 mm and 2.5 mm respectively (middle part), enabling delivery through the working channel of the resectoscope. The beginning part of the injector was connected to a 20-ml syringe containing methylene blue solution as the injection fluid.

HPL-ESD procedure: All surgeries were conducted in the lithotomy position under continuous epidural anesthesia. Sodium chloride physiological solution was used for irrigation. The 23F continuous flow resectoscope was delivered into the bladder through the urethra initially. Each visible tumor was examined to confirm the location, number, and size and the condition of the adjacent mucosa. Then, the 6F green-light LBO laser fiber was delivered through the working channel of the resectoscope. Each tumor was first marked with a circular coagulation blockage border, which was 1-2 cm from the edge of the tumor. Next, the laser fiber was temporarily withdrawn and the disposable injector was delivered through the same working channel of the resectoscope. Multipoint injection was performed in the normal mucosa along the blockage border. Because the tissue between the mucosal layer and the detrusor muscle layer in the bladder wall is relatively loose, a blue submucosal fluid cushion was formed between the two layers after injection. Subsequently, the green-light laser was delivered through the working channel again. The laser power was set at 160 W for cutting and 30-50 W for coagulation simultaneously. The mucosa was incised annularly, and the detrusor muscle layer beneath it was gradually exposed. The submucosal fluid cushion separated the mucosa layer and the detrusor muscle layer to some extent in advance. Therefore, the course and distribution of the detrusor muscle could be clearly observed. Dissection of tissue connected between the tumor and the bladder wall was also facilitated. The entire tumor was excised with superficial detrusor muscle beneath the basal part. After resection, the whole tumor bed and surrounding mucosa were carefully coagulated at a power of 30-50 W. The intact bladder tumor was removed with an alligator forceps or flushed out with an Ellik evacuator. When the tumor size was \> 3 cm, the specimen was longitudinally cut into two or more parts.

Clinical data will be collected, such as patient data, tumor characteristics, and perioperative data.