Editorial Comment on: “ In Vitro Dusting Performance of a New Solid State Thulium Laser Compared to Holmium Laser Lithotripsy” by Petzold,et al.

Dear Editor:

We have read with interest the article recently published in the Journal of Endourology by Petzold et al. ¹ regarding an in vitro laser lithotripsy comparison between a pulsed thulium:yttrium aluminum garnet laser (Tm:YAG) and a pulsed holmium:yttrium aluminum garnet laser (Ho:YAG). The study revealed similar dusting performance for both laser devices at comparable laser settings. In addition, the authors found a superior ablation efficiency using the longer pulse duration, higher frequency, and lower single pulse energy range of the Tm:YAG laser, thus presenting the Tm:YAG laser as a promising device for “highly efficient fine dusting in conjunction with low retropulsion.”

Nowadays, talking about holmium and thulium lasers in endourology could be confusing. To clarify, we should specify that we have:

solid state lasers such as the Tm:YAG and Ho:YAG that use the doping element (holmium or thulium) in a laser crystal ² ;

fiber lasers such as thulium fiber laser (TFL) that consist of a rare-earth-doped optical fiber coated with a low-index polymer (in this case, Tm₂O₃ and additional dopants such as Al₂O₃ in a silica matrix) ³ ;

technologies, machine sizes, performances, settings, and costs are different between these lasers. It is not the aim of this editorial comment to go through laser specifics, but this concept has to be clear to the reader.

In Petzold et al. article, some considerations about the “Thulium” and “Holmium” laser nomenclature have to be done here.

In their introduction section, the authors state that “In the shadow of Ho:YAG laser lithotripsy, TFLs have been investigated for more than 15 years and shown comparable results for stone ablation and low retropulsion.” At this point, it should be noted that ablation efficiency and retropulsion profile were not only “comparable,” but were consistently found superior in favor of the TFL in several studies, when compared with Ho:YAG. ^3,4

We do not understand why the authors are referring to the TFL in this study, considering that none of the experiments were based on the TFL. Hazardous and hypothetical comparisons between TFL and Tm:YAG were made in the discussion section, whereas the authors did not provide any experimental data to draw such conclusions. The claims on the “low retropulsion” properties of the Tm:YAG are completely hypothetical and are not based on any experimental data from this study. Finally, the authors only made vague references to the laser systems used for their study in the introduction section. A detailed description with product and brand names of laser systems and laser fibers are completely missing the methodology section. This lack of information is in sharp contrast to the exhaustive and detailed experimental setup.

Considering the aforementioned, it seems that the authors are making confusing claims, which may complicate the understanding of TFL, constant wave Tm:YAG, and pulsed Tm:YAG laser technologies. Urologists are not meant to become engineers, and most of us are not necessarily familiar with all different lasers on the market. Therefore, it should be of primary importance to be clear while discussing and reporting on lasers, especially adequately referring to machines that may be based on the same ion (e.g., thulium), but not on the same technology (e.g., solid state lasers such as the Tm:YAG and Ho:YAG vs fiber lasers such as the TFL).

We congratulate the authors for their original study, which generally seems to be based on a sound methodology and, therefore, may provide important results to the scientific target audience. It is not the aim of this comment to judge the experiment rolled out, but to raise awareness about the need for clear, correct, and understandable laser nomenclature in the field of endourology.