Photoselective vaporization of the prostate (PVP) has been developed for effective treatment of obstructive benign
prostatic hyperplasia. To maximize tissue ablation for large prostate gland, identifying the optimal power level for PVP
is still necessary. We investigated the effect of various power levels on in vitro bovine prostate ablation with a 532-nm
laser system. A custom-made 532-nm laser was employed to provide various power levels, delivered through a newly
designed 750-μm side-firing fiber. Tissue ablation efficiency was evaluated in terms of power (P; 120~200W), treatment
speed of fiber (TS; 2~8 mm/s), and working distance between fiber and tissue surface (WD; 1~5 mm). Coagulation
depth was also estimated macroscopically and histologically (H&E) at various Ps. Both 180 and 200W yielded
comparable ablated volume (104.3±24.7 vs. 104.1±23.9 mm3 at TS=4 mm/s and WD=2 mm; p=0.99); thus, 180W was
identified as the optimal power to maximize tissue ablation, by removing tissue up to 80% faster than 120W (41.7±9.9
vs. 23.2±3.4 mm3/s at TS=4 mm/s and WD=2 mm; p<0.005). Tissue ablation was maximized at TS=4 mm/s and ablated
equally efficiently at up to 3 mm WD (104.5±16.7 mm3 for WD=1 mm vs. 93.4±7.4 mm3 for WD=3 mm at 180W;
p=0.33). The mean thickness of coagulation zone for 180W was 20% thicker than that for 120W (1.31±0.17 vs.
1.09±0.16 mm; p<0.005). The current in vitro study demonstrated that 180W was the optimal power to maximize tissue
ablation efficiency with enhanced coagulation characteristics.
Photoselective vaporization of the prostate (PVP) has been widely used to treat benign prostatic hyperplasia (BPH). It is
well regarded as a safe and minimally invasive procedure and an alternative to the gold standard transurethral resection
of the prostate (TURP). Despite of its greatness, as well aware of, the operative procedure time during the PVP is still
prolonged. Such attempts have been tried out in order to shorten the operative time and increase its efficacy. However,
scientific study to investigate techniques used during the PVP is still lacking. The objective of this study is to investigate
how sweeping angle might affect the PVP performance. Porcine kidneys acquired from a local grocery store were used
(N=140). A Q-switched 532-nm GreenLight XPSTM (American Medical Systems, Inc., MN, USA), together with 750-
μm core MoXyTM fiber, was set to have power levels of 120 W and 180 W. Treatment speed and sweeping speed were
fixed at 2 mm/s and 0.5 sweep/s, respectively. Sweeping angles were varied from 0 (no sweeping motion) to 120 degree.
Ablation rate, depth, and coagulation zone were measured and quantified. Tissue ablation rate was peaked at 15 and 30
degree for both 120- and 180-W power levels and dramatically decreased beyond 60 degree. At 180 W, ablation rate
increased 20% at 30 degree compared to 0 degree. This study demonstrated that ablation rate could be maximized and
was contingent upon sweeping angle.
Photoselective vaporization of the prostate (PVP) is considered a minimally invasive procedure to treat benign prostatic
hyperplasia (BPH). During the PVP, the prostate gland is irradiated by the 532-nm laser and the fiber is swept and
dragged along the urethra. In this study the speed of sweeping fiber during the PVP is being investigated. In vitro
porcine kidney model was used (N=100) throughout the experiment. A Q-switched 532-nm laser, equipped with sidefiring
750-Um fiber, was employed and set to power levels of 120 and 180 W. The speed of fiber sweeping was the only
variable in this study and varied at 0 (i.e. no sweeping), 0.5, 1.0, 1.5, and 2.0 sweep/s. Ablation rate, depth, and
coagulation thickness were quantified. Based on the current settings, ablation rate decreased as sweeping speed increased
and was maximized between 0 to 1.0 sweep/s for 120-W power level and between 0 to 0.5 sweep/s for 180-W power
level. Ablation rate at 180 W was higher than that at 120 W, regardless of sweeping speed. Ablation depth at both 120
and 180 W was maximized at 0 sweep/s and decreased 35% at 0.5 sweep/s. The overall coagulation thickness was less
than 1.5 mm and comparable from 0 to 1.5 sweep/s (0.8~0.9 mm) and increased at 2.0 sweep/s (~1.1 mm). This study
demonstrated that tissue ablation performance was contingent upon sweeping speed and maximized at slow sweeping
speed due to longer laser-tissue interaction time and larger area coverage by the 532-nm light.
A novel MoXyTM fiber delivery device with Active Cooling Cap (ACCTM) is designed to
transmit up to 180W of 532 nm laser light to treat benign prostatic hyperplasia (BPH). Under
such high power tissue ablation, effective cooling is key to maintaining fiber power transmission
and ensuring the reliability of the fiber delivery device To handle high power and reduce fiber
degradation, the MoXy fiber features a larger core size (750 micrometer) and an internal fluid
channel to ensure better cooling of the fiber tip to prevent the cap from burning, detaching, or
shattering during the BPH treatment. The internal cooling channel was created with a metal cap
and tubing that surrounds the optical fiber. In this study MoXy fibers were used to investigate
the effect of power levels of 120 and 200 W on in-vitro bovine prostate ablation using a 532 nm
XPSTM laser system. For procedures requiring more than 100 kJ, the MoXy fiber at 200W
removed tissue at twice the rate of the current HPS fiber at 120W. The fiber maintained a
constant tissue vaporization rate during the entire tissue ablation process. The coagulation at
200W was about 20% thicker than at 120W. In conclusion, the new fibers at 200W doubled the
tissue removal rate, maintained vaporization efficiency throughout delivery of 400kJ energy, and
induced similar coagulation to the existing HPS fiber at 120W.
A previous in vitro study demonstrated that 180W was the optimal power to reduce photoselective vaporization of the
prostate (PVP) time for larger prostate glands. In this study, we investigated anatomic and histologic outcomes and
ablation parameters of 180W laser performed with a new 750-μm side-firing fiber in a survival study of living canines.
Eight male canines underwent anterograde PVP with the 180W 532-nm laser. Four each animals were euthanized 3
hours or 8 weeks postoperatively. Prostates were measured and histologically analyzed after hematoxylin and eosin
(H&E), triphenyltetrazolium chloride (TTC), or Gomori trichrome (GT) staining. Compared to the previous 120W laser,
PVP with the 180W laser bloodlessly created a 76% larger cavity (mean 11.8 vs. 6.7 cm3; p=0.014) and ablated tissue at
a 77% higher rate (mean 2.3 vs. 1.3 cm3/min; p=0.03) while H&E- and TTC-staining demonstrated its 33% thicker mean
coagulation zone (2.0±0.4 vs. 1.5±0.3 mm). H&E-stained cross-sectional prostatic tissue specimens from the 3-hour
(acute) group showed histologic evolution of concentric non-viable coagulation zone, partially viable hyperemic
transition zone of repair, and viable non-treated zone. H&E- and GT-stained specimens from the 8-week (chronic) group
revealed healed circumferentially epithelialized, non-edematous, prostatic urethral channels with no increase in collagen
in the subjacent prostatic tissue vis-á-vis the normal control. Our canine study demonstrates that 180W 532-nm laser
PVP with its new fiber has a significantly higher ablation rate with a more hemostatic coagulation zone, but equally
favorable tissue interaction and healing, compared with our previous 120W canine study.
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