<title>Partial response to laser-induced thermotherapy: incidence of biliary structures</title>

Twenty VX2 tumors were grafted on 10 rabbit livers. The animals were randomized in two groups when tumor size reached 8 mm. Thermotherapy was performed by delivering the 830 nm output of a diode laser in the center of the tumor using a 300 micrometers fiber. Irradiation conditions were 1.5 W over 900 s. On day 7 or day 14 tumors were removed, stained using hematoxylin eosin and picrosirius red F3BA. Electronic microscopy examination was also preformed. Among the treated tumors, recurrences were found both at the periphery and within the tumors. All recurrences were located near biliary structures. The thermal damage was evaluated by the picrosirius red F3BA stain. Electronic microscopy indicated the thermal resistance of the biliary ducts in the vicinity of coagulative necrosis. The biliary ducts themselves or the vasculature surroundings the ducts lead to a heat sink, thus limiting the tissue temperature elevation. Thermal dosimetry as MRI using thermo sequences should be developed to insure efficient thermotherapy.