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Laser immunotherapy (LIT) was developed to treat metastatic cancers using a combination of laser
irradiation and immunological stimulation. The original design of LIT employs a non-invasive, selective
laser photothermal interaction, using an in situ light-absorbing dye. However, this non-invasive treatment
mode faces challenges in treating deep, large tumors. Furthermore, it has difficulties in the cases of highly
pigmented skin overlying target tumors. To overcome these limitations, interstitial laser immunotherapy
(ILIT) was proposed. In ILIT, a cylindrical, side-fire fiber diffuser is placed inside the target tumor to
induce thermal damage. To enhance the interstitial irradiation induced photothermal interaction, an
immunological modifier, glycated chitosan (GC), is injected into the tumor after the laser treatment. In this
study, a cylindrical diffuser with an active length of 1 cm was used to treat tumors of 1 to 1.5 cm in size.
Different laser powers (1 to 3 watts) and different irradiation durations (10 to 30 minutes) were used to test
the thermal effects of ILIT. Different doses of the GC (1.0%, 0.1 to 0.6 ml per rat) were used to determine
the immunological effects of ILIT. Our results show that the animal survival depends on both laser dose
and GC dose. A dose of 0.2 ml per tumor appeared to result in the highest survival rate under interstitial laser irradiation with 2.5 watts and 20 minutes. While the results in this study are not conclusive, they
indicate that interstitial laser irradiation can be combined with immunotherapy to treat metastatic cancers.
Furthermore, our results suggest that an optimal combination of laser dose and GC dose could be obtained
for future clinical protocols using interstitial laser immunotherapy.
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