Abstract
Photothermal therapy (PTT) using a photo-absorbent in the near-infrared (NIR) region is an effective methodology for local cancer treatment. Before PTT using a NIR absorbent is executed, the operator generally determines the two parameters of fluence rate and irradiation time. However, even if the irradiation parameters are unchanged, the therapeutic effect of PTT is often different for individual tumors. Hence, we examined the therapeutic effect of PTT using a NIR absorbent (ICG lactosome) while changing two parameters (fluence rate and irradiation time) in various combinations. As a result, there was no robust correlation between those parameters and the therapeutic effect. Compared to those parameters, we found that a more reliable determinant was maintenance of the tumor temperature above 43 °C during NIR irradiation. To reconfirm the significance of the determinant, we developed a new system that can regulate the temperature at the NIR irradiation site at a constant level. By using the new system, we verified the treatment outcomes for tumors in which the NIR absorbent had accumulated. All of the tumors that had been kept at 43 °C during NIR irradiation were cured, while none of the tumors that had been kept at a temperature below 41 °C were cured. In conclusion, PTT using a NIR absorbent with thermal dosimetry is a highly reliable treatment for cancer.
Highlights
Photothermal therapy (PTT) using a photo-absorbent in the near-infrared (NIR) region is an effective methodology for local cancer treatment
As the first step for the pursuit of an optimal method, we studied the outcomes of PTT using a drug delivery system (DDS)-type NIR absorbent for cancer tumors when irradiation parameters were changed
Negative correlations between fluence rate and tumor size were seen at irradiation times of 333 s (r = −0.715, P < 0.0004) and 1000 s (r = −0.653, P < 0.0018), while there was no significant correlation between fluence rate and tumor size at irradiation times of 111, 222 and 666 s (Fig. 1A)
Summary
Photothermal therapy (PTT) using a photo-absorbent in the near-infrared (NIR) region is an effective methodology for local cancer treatment. Before PTT using a NIR absorbent is executed, the operator generally determines the two parameters of fluence rate and irradiation time. There was no robust correlation between those parameters and the therapeutic effect Compared to those parameters, we found that a more reliable determinant was maintenance of the tumor temperature above 43 °C during NIR irradiation. When executing PTT using a DDS-type NIR absorbent, the tumor is irradiated with a NIR light at a certain time after administration of the absorbent Irradiation parameters such as fluence rate and irradiation time in PTT are generally determined prior to NIR irradiation. As the first step for the pursuit of an optimal method, we studied the outcomes of PTT using a DDS-type NIR absorbent for cancer tumors (cure/growth) when irradiation parameters (fluence rate and irradiation time) were changed. We developed a new PTT treatment system of which the working principle fulfills the determinant, and we obtained complete regression of tumors by using the system
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