Diffusing fibre tip for the minimally invasive treatment of liver tumours by interstitial laser coagulation (ILC): An experimental ex vivo study

A newly developed diffusing laser applicator was examined for interstitial laser coagulation (ILC) of liver tumours. The applicator consisted of a matted quartz core and a quartz glass dome, also matted on its inner surface and sealed to the fibre. The applicator provided a homogeneous light intensity distribution over an active length of about 20 mm. Lesions were created in an ex-vivo porcine liver model using a Nd-YAG laser comparing the new diffusing tip with a Ringmode(R)-ITT applicator in order to find optimal laser parameters and damage thresholds. The lesions were investigated using macroscopic size measurement, volume calculation and histological examination (H&E, NADPH-dehydrogenase). The damage threshold of the diffusing tip was 6 W at 14 min exposure time whereas the Ringmode(R)-ITT applicator had its limit at 5 W and 12 min exposure. Comparing various exposure times showed that treatment over a time of more than 840 s did not significantly increase the lesion volume. At 5 W and 720 s the mean lesion volume was 6.9 +/- 1.1 cm(3) with the diffusing tip and 6.3 +/- 0.6 cm(3) with the Ringmode(R)-ITT applicator, both having a slight ellipsoidal shape. Hence,the created lesions were not significantly different for both applicators when the same laser parameters were applied. On the other hand, the new diffusing tip had a higher damage threshold and was therefore capable of producing maximal coagulation volumes of up to 7.9 +/- 0.5 cm(3) at 5 W and 20 min. The experiments showed that lesions with a dimension of 31 x 22 mm can be achieved with. the diffusing applicator which seem suitably sized for treating small human liver metastases in a single laser session.