TREATMENT OF MALIGNANT-MELANOMA BY HIGH-PEAK-POWER 1064 NM IRRADIATION FOLLOWED BY PHOTODYNAMIC THERAPY

Irradiation of B16 pigmented melanoma subcutaneously transplanted in C 57 mice with a single 650 mJ pulse (10 ns) of 1064 nm light from a Q-s witched Nd:YAG laser caused instantaneous bleaching of the pigmented t issue. Visual and histological examination of the resulting gray-color ed tumor revealed the breakdown of melanosomes with no detectable alte ration of the normal and tumor-overlying skin, Histological examinatio n of the irradiated tumor showed some degree of vascular damage; the d epth of the photodamage was not affected by the successive delivery of three consecutive light pubes. The bleached tumor grew at a modestly slower rate but the high-peak-power (HPP) laser treatment did not affe ct the tumor concentration of a photodynamic sensitizer SI(IV)naphthal ocyanine (isoBO-SiNc) intravenously injected 24 h before Nd:YAG irradi ation. Treatment of the B16 pigmented melanoma by photodynamic therapy (PDT: 1 mg/kg isoBO-SiNc, 300 mW/cm(2), 520 J/cm(2)) from a 774 nm di ode laser immediately after the 1064 nm irradiation resulted in a 16 d ay delay of tumor regrowth, which was markedly longer than the delay ( ca 6 days) obtained after PDT under identical conditions without the p reirradiation, Thus, pretreatment of pigmented tumors with HPP 1064 nm light appears to enhance their susceptibility to conventional PDT, Th e tumor response was further enhanced by repeating the combined HPP/PD T treatment at an interval of 10 days (regrowth delay: 27 days), as we b as by applying hyperthermia immediately after HPP/PDT (regrow-th del ay: ca 34 days).