INTERSTITIAL LASER THERMOTHERAPY - COMPARISON BETWEEN BARE FIBER AND SAPPHIRE PROBE

A sapphire probe and a bare fibre were compared with respect to temper ature control and distribution and light fluence in interstitial laser thermotherapy. Experiments were performed in processed liver using an Nd-YAC; laser and output power levels of 1-4 W. The temperature was c ontrolled at a distance of 10 mm using a feedback circuit with an auto matic thermometry system and thermistor probes. With the sapphire prob e, carbonization was rare at power levels of 1-2 W but was observed in half of the experiments at 3 W and in all experiments at 4 W, Using t he bare fibre, carbonization was seen in almost all experiments. Absen ce of carbonization was associated with a moderate decrease in the pen etration of light and excellent control of the temperature, whereas ca rbonization led to rapid impairment of light penetration and temperatu re control. In addition, the temperature gradient was smaller with the sapphire probe than with the bare fibre or when carbonization was abs ent. It is concluded that a diffuser tip, such as the sapphire probe, may be preferable to the bare fibre for interstitial laser thermothera py because it gives a smaller temperature gradient and helps to avoid carbonization which results in preserved light penetration and improve d temperature control.