Interstitial diode laser hyperthermia in the treatment of subcutaneous tumor

Background and Objective: Interstitial Laser Hyperthermia (ILH) has been investigated since the early 80s in the treatment of deep seated tumors. The purpose of this study was to evaluate the efficiency of diode ILH (830 nm) in a subcutaneous tumor model. Study Design/Materials and Method: The antitumoral effect of diode ILH was assessed in a randomized study performed on 80 Swiss nu/nu mice. The tumor model was a subcutaneously implanted HT29 colonic carcinoma. The animals were assigned to four groups of 20 mice: Groups I and 3 were treated by ILH, groups 2 and 4 were not treated (control groups). Tumors were removed on day 3 in groups 1 and 2, and on day 30 in groups 3 and 4. The treatment was performed on tumors of 8 mm in diameter and a volume of 140 mm(3). A laser irradiation of 360 J (power: 0.2 W; irradiation time: 1 800 s) was delivered through a 300 mu m optical fiber implanted in the tumor. The laser parameters insured temperatures of 46 degrees C in the central part of the tumor and 42 degrees C at the periphery. Tumor features were evaluated on day 3 and day 30. Results: Untreated tumors grew rapidly up to a mean volume of 241 mm(3) on day 3 (group 2) and 2,000 mm(3) on day 30 (group 4). Treated tumors regressed to a mean volume of 32 mm(3) on day 3 (group 1). On day 30, 40% of the tumors had totally disappeared and 60% showed partial response with small and peripheral residual tumor of 172 mm on an average, as to say 11.2 times smaller than in group 4. Conclusion: ILH with a low power 830 nm diode laser is an efficient treatment of subcutaneous tumor model. Partial responses are attributed to an insufficient heating at the tumor periphery. More precise control of the peripheral tumor temperature will improve the ILH results. (C) 1996 Wiley-Liss, Inc.