2008 Volume 29 Issue 1 Pages 5-11
To discuss the feasibility of performing percutaneous interstitial laser treatment as a minimally invasive therapy for thyroid micro cancer, we investigated the correlation between the power/energy and treatment effect, and measured fluctuations in the internal and superficial temperature of thyroid tissues using experimental animals.
A laser fiber was inserted through an introducer needle into a pig's thyroid, and photoablation was performed with a diode laser emitting light at a wavelength of 830nm. After formalin fixation, the mean diameter of the necrosis was measured. Using 2W at fiber tip, there is no correlation between irradiational condition and necrosis. At 3W and 5W, the necrotic area enlarged in proportion to increased energy (J) producing a spindle-shaped lesion over the fiber tip. Using the same energy, a larger necrosis was consistently produced at 3W. However, there was no significant difference in the size of necrosis when treated for the same length of time. The largest necrosis of 12.3 mm was produced at 3W, 1500J. At 5 mm (necrotic site), 10 mm (peripheral of necrotic site), and 15 mm (non-necrotic site) from treatment point, the temperature within the tissue reached maximum, 300 seconds after laser delivery. At 3W, the temperature increased moderately, measuring 160°C, 81°C and 54°C respectively. At 5W, the temperature increased rapidly to 154°C, 64°C, 46°C respectively. Carbonization was seen around the fiber tip at 5W. The surface temperature of thyroid was 38°C at 3W, and 55°C at 5W.
Interstitial laser treatment enables ablation of thyroid tissue up to 1 cm in diameter using 3W for 5 minutes without increased surface temperature or carbonation-induced attenuation in laser transmission, suggesting that this can be a minimally invasive therapy enforceable for outpatients by using the portable diode laser under ultrasound guidance.
