Fluence as a Function of Weight: A Photobiomodulation Therapy (PBMT) Spinal Cord Injury (SCI) Rat Model—A Computational Study

A spinal cord injury (SCI) is caused by damage to neurons in the spinal cord, which interrupts neural signal conduction via axonal tracts, causing either total or partial paralysis. Researchers have proven that photobiomodulation therapy (PBMT) can affect nerve repair, causing enhanced functionality. Many PBMT studies have examined contusion SCIs in rats by employing a fixed fluence applied to the skin over the course of the treatment without considering the animal weight, which could affect the fluence delivered to the SCI site. This study performed Monte Carlo simulations using four computer-simulated rat models, all 11 weeks of age but each one having a different weight, and used various irradiation parameters to assess the impact of these factors on the fluence delivery at the SCI site. When the weight of the rat decreased, the fluence delivered to the SCI site increased. The findings also demonstrated that the greatest percentage rise in the fluence delivered to the SCI site occurred when employing a 660 nm Gaussian beam. The rat weight and irradiation parameters had a significant effect on the fluence delivered to the SCI site in rats. Thus, when assessing the effectiveness of PBMT, researchers must consider how much fluence reaches the injury site rather than how much fluence is applied to the skin.