Coupled effects of multi-pulse laser irradiation and hyaluronic acid spacer thickness on rectal wall thermal damage during prostate cancer therapy using a GDPL bioheat model

Laser-induced thermal therapy is a promising minimally invasive option for localized prostate cancer, yet excessive heat diffusion to the rectal wall remains a critical safety concern. While hyaluronic acid (HA) spacers are commonly used to mitigate rectal heating, the combined influence of spacer thickness and temporal laser modulation has not been systematically clarified. This study developed a numerical framework to investigate the coupled effects of continuous and multi-pulse laser irradiation with varying HA spacer thicknesses on rectal wall temperature and thermal damage. The generalized dual-phase-lag (GDPL) bioheat model was employed to capture non-Fourier heat transfer in biological tissue, and thermal injury was quantified using an Arrhenius damage model. Compared with continuous irradiation, multi-pulse modes markedly reduced both the peak rectal wall temperature and thermal damage. Without an HA spacer, the maximum rectal wall temperature decreased by 10.2%, 15.7%, and 20.4% for the 2-pulse, 3-pulse, and 4-pulse modes, respectively, while the corresponding thermal damage decreased by 16.9%, 25.4%, and 26.6%. The results further showed that increasing pulse number could partially compensate for reduced HA thickness. An HA spacer thickness of 3–4 mm was identified as sufficient for effective rectal wall protection. These findings provide practical guidance for improving safety and optimizing spacer usage in prostate laser therapy.