Introduction: When stone popcorning, the use of higher energy with little to no irrigation is preferred. However, this combination of high power with low flow can lead to increased risk of thermal damage with longer laser firing times. Using predetermined lasering and irrigation ‘cool down’ durations within a novel, anatomically accurate 3D kidney model, our aim was to identify the laser settings that produce the most efficient popcorning without reaching thermal dose (t43) that causes tissue damage.
Methods: Hard Begostone phantoms, mimicking calcium oxalate monohydrate stones, were crushed and sieved to 2-4mm fragments. Fragments were then separated by size measuring 2-2.8mm, 2.8-3.35mm, and 3.35-4mm and mixed by mass at a ratio of 2:2:1, respectively. Approximately 0.5g of fragments were placed in the upper pole of our anatomical 3D-printed kidney model. Each triplicate trial consisted of iterative laser/irrigation cooling cycles for two minutes using a MosesTM 120H 2.0 laser (Table). Laser firing and cooling times were determined by measuring t43 with each laser setting, allowing for maximal laser to cooling ratio that would not exceed tissue injury threshold (t43 70 min). After treatment, stones were dried and sieved into <1mm, 1-2mm, 2-2.8mm, 2.8-3.35, and 3.35-4mm fragments, which were then weighed. Ablation efficiency was calculated as post-treatment mass <1mm, with comparisons by ANOVA and Tukey post-hoc tests.
Results: Overall, the most efficient setting was 0.5J/90Hz with no irrigation; while the most efficient setting using low irrigation were 0.4J/110Hz and 0.5/J/80Hz SP (Figure). Even with shorter laser times, popcorning was more efficient with no irrigation, especially at high powers (all p<0.05).
Conclusions: When accounting for thermal dose, 0.5J/90Hz without irrigation provides the most efficient popcorning, despite shorter laser times. When thermal injury is of special concern and the surgeon prefers low flow, 0.4J/110Hz appears most efficient. Last, if extended frequency is unavailable, 0.6J/80Hz without irrigation should be used.
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