Investigation of photodynamic therapy dependence on fluence rate using photoacoustic imaging

This study investigates the fluence rate effect of photodynamic therapy (PDT) by using photoacoustic imaging method, which enables subtle biological responses, including vascular damage, inflammation reaction and self-healing response to be studied. Our results reveal the correlations between fluence rate and PDT efficacy/self-healing magnitude, indicating that vascular injuries induced by high fluence rate PDT are more likely to recover and by low fluence rates are more likely to be permanent. There exists a turning point (278mW), above which PDT practically produces no permanent therapeutic effect and damaged vessels can fully recover. These findings have practical significance in clinical setting. For cancer-related diseases, the ‘effective fluence rate’ is useful to provoke permanent destruction of tumor vasculature. Likewise, the ‘non effective range’ can be applied when PDT is used in applications such as opening the blood brain barrier to avoid permanent brain damage.