In search of optimal settings for Ho:YAG laser- lithotripsy to maximize the ablation rate, while minimizing the retropulsion

摘要

Although laser lithotripsy is now the preferred treatment option for urolithiasis due to shorter operation time and a betterstone-free rate , the optimal laser settings for URS (Ureteroscopic lithotripsy) to enable shorter operating times remainunclear. This study aims to identify optimal laser settings for Ho:YAG laser-lithotripsy to maximize the ablation ratewhile minimizing the retropulsion, as well as to improve the discharge of fragments via the urinary tract. The net resultwill be an increase in treatment success and patient satisfaction by ameliorating the stone-free rate.In vitro investigations of Ho:YAG laser-induced stone ablation and retropulsion were performed with a bench top modelfirst introduced by Sroka’s group . A commercial Ho:YAG laser system (Lumenis VersaPulse® PowerSuite™ 100W,Lumenis Ltd., Yokneam, Israel) was used as the laser pulse source, with pulse energy from 0.2 J up to 1.5 J andrepetition rate from 5 to 40 Hz. A DOE with two replicate points and two lack-of-fit points was performed on artificialBEGO stones of sample size 14 under reproducible experimental conditions (fiber size: 365 μm, S-LLF365 SureFlexFiber, Boston Scientific Corporation, San Jose, CA, USA). The best fit to the experimental data was analyzed utilizingthe design of experiment software, which can produce the numerical formulas for the response surfaces of ablation rateand retropulsion in terms of laser pulse parameters .The coded numerical formulas for the response surfaces of ablation speed and retropulsion velocity are generated. Thecoded equation is useful for identifying the relative impact of the factors by comparing their coefficients. Uponexamination of the laser ablation of stone phantoms (BEGO) , the laser pulse energy is 1.4 times the impact of thefrequency, and laser pulse peak power’s impact is the same as the frequency; while for retropulsion, the laser pulseenergy is 5.8 times as the impact of the frequency, and laser pulse peak power’s impact is 13 times as the frequency; Aseries of laser settings for relatively efficient laser lithotripsy were identified in terms of laser pulse energy and peakpower.The laser pulse energy or peak power in reference to frequency has a higher impact coefficient to stone retropulsion ascompared to stone ablation in Ho:YAG laser-lithotripsy. The most effective way to reduce stone retropulsion duringlaser lithotripsy is to reduce the laser pulse peak power (which has the highest impact coefficient in the coded responseequation).