267. ETHNIC VARIABILITY IN RTMS DOSAGE: A CALL FOR ADAPTIVE THERAPEUTIC INNOVATION

Abstract Background Repetitive transcranial magnetic stimulation (rTMS) targeting the left dorsolateral prefrontal cortex (DLPFC) is a widely used adjunctive therapy for various neurological and psychiatric disorders. Traditionally, the standard practice for dosing rTMS has involved adjusting its intensity to a defined percentage of the motor threshold. However, potential anatomical differences among ‘White’, ‘Han Chinese’ and ‘Black or African American’ ethnic groups may result in unequal doses of stimulation at the left DLPFC, a prime target for therapeutic rTMS. Aims & Objectives We aimed to investigate ethnic differences in anatomical head morphology and transcranial magnetic stimulation (TMS) induced electric fields at the left DLPFC and the left primary motor cortex (M1). Method We examined the scalp-to-cortex distances (SCD) and the strength of TMS induced electric fields at the left DLPFC and the left M1 in anatomical brain scans among three ethnic groups (aged 22-35 years): 821 ‘White’, 165 ‘Black or African American’, and 159 ‘Han Chinese’ individuals (Anatomical neuroimaging data taken from the Human Connectome Project and Chinese Human Connectome Project). Results Our results indicate that the ‘White’ individuals had a larger mean SCD ratio (mean F3 SCD/ mean C3 SCD) than both the ‘Han Chinese’ and the ‘Black or African American’ individuals (p’s < 0.001). Analysis of electric field strength showed that ‘White’ individuals received a lower mean electrical field strength ratio (mean F3 electric field strength/mean C3 electric field strength) than ‘Han Chinese’ individuals and ‘Black or African American’ individuals (p’s < 0.001). Discussion & Conclusions Our research revealed significant ethnic differences in SCD and TMS dosage reaching the brain. These differences may contribute to the varying therapeutic effects of rTMS reported in the literature and highlight a potential bias in existing research comparing its efficacy across ethnicities. More importantly, our results emphasize the need to tailor rTMS safety guidelines for diverse ethnic populations.