Thermal effects of thulium: YAG laser treatment of the prostate—an in vitro study

Abstract

Purpose To objectively determine whether there is potential thermal tissue damage during Tm:YAG laser-based LUTS treatment. Methods Our experimental model was comprised of a prostatic resection trainer placed in a 37 °C water bath. In a hollowed-out central area simulating the urethral lumen, we placed a RigiFib 800 fibre, irrigation inflow regulated with a digital pump, and a type K thermocouple. A second thermocouple was inserted 0.5/1 cm adjacently and protected with an aluminum barrier to prevent it from urethral fluid. We investigated continuous and intermittent 120 W and 80 W laser application with various irrigation rates in eight measurement sessions lasting up to 14 min. Thermal measurements were recorded continuously and in real-time using MatLab. All experiments were repeated five times to balance out variations. Results Continuous laser application at 120 W and 125 ml/min caused a urethral ∆T of ~ 15 K and a parenchymal temperature increase of up to 7 K. With 50 ml/min irrigation, a urethral and parenchymal ∆T of 30 K and 15 K were reached, respectively. Subsequently and in absence of laser application, prostatic parenchyma needed over 16 min to reach baseline body temperature. At 80 W lower temperature increases were reached compared to similar irrigation but higher power. Conclusions We showed that potentially harming temperatures can be reached, especially during high laser power and low irrigation. The heat generation can also be conveyed to the prostate parenchyma and deeper structures, potentially affecting the neurovascular bundles. Further clinical studies with intracorporal temperature measurement are necessary to further investigate this potentially harming surgical adverse effect.

A prospective analysis of thulium laser enucleation in benign prostatic hyperplasia comparing low- and high-power approaches for prostates exceeding 80 g

“…The authors also looked into the penetration depth—increasing laser power correlation—and found that more laser power could bring about more penetration depth and related laser damage zone, though it is highly controllable, especially with pulsed TmL which creates less carbonization than the continuous-wave TmL. In another in vitro experimental study, Hein and his colleagues attempted to assess the thermal effect of TmL and concluded that adverse thermal injury could be reached especially with high-power laser and low irrigation fluid volume and the generated heat could invade the prostate tissue with a potential harm to the nearby neurovascular bundles [ 21 ]. However, in consistence with the present study, Dmitry Enikeev and his colleagues found, through a clinical trial comparing thulium laser prostate vaporization (using 120 W) and conventional monopolar TURP, that TmL vaporization could preserve or even improve the erectile function after successful bladder outlet reduction [ 22 ].…”

Temperature assessment study of ex vivo holmium laser enucleation of the prostate model

“…Although there have been studies investigating the thermal effects of thulium and holmium:YAG lasers, the number of published studies on heat generation during HoLEP and its associated risks is insufficient [ 13 , 14 ]. In the present study, we investigated the temperature development during HoLEP ex vivo employing two different experimental models.…”

“…The existing studies have mainly investigated ex vivo temperature generation during laser application, but with different experimental setups and aims. In an in vitro model, Hein et al investigated the thermal effects of Tm:YAG laser treatment of the prostate [ 13 ]. They found a 15 K temperature increase in the urethra and up to 7 K parenchymal temperature increase using continuous laser application at 120 W and a 125 ml/min irrigation flow rate.…”