Effects of Irradiation Parameters and Position on Photobiomodulation Therapy for Spinal Cord Injury Rat Phantom...

To optimize photobiomodulation therapy (PBMT) for spinal cord injury (SCI) by studying the effect(s) of irradiation parameters and position of PBMT on injury site using Monte Carlo simulation and a three-dimensional voxelated SCI rat phantom model. Several studies used a range of irradiation parameters and surface irradiances to calculate the fluence delivered to the SCI site. However, most have ignored factors such as the optical properties of tissues, irradiation parameters, and position. Therefore, although such studies present a broad range of treatment outcomes, a comparison of the treatment efficacy concerning the applied fluence using these studies presents certain challenges In this study, an 810 nm top-hat beam was simulated for 5 numerical apertures (NAs; 0.0, 0.2, 0.4, 0.6, and 0.8), 10 beam radii (0.001, 0.01, 0.1, 0.25, 0.5, 1, 2.5, 5, 10, and 25 mm), and 17 different irradiation positions relative to the SCI site. The beam radius and position strongly affect the accumulated fluence within the injury site, whereas the NA appears to have a smaller effect on the accumulated fluence within the injury site. A large probe beam produces a uniform fluence distribution reaching the injury site, minimizing the effect of misplacing the probe at the center of the injury. Our findings will be beneficial to understanding the effects of irradiation parameters on tissues and organs, which will help reduce variability in the fluence applied to injury sites and will help optimize PBMT outcomes.