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 mat ted quartz core and a quartz glass dome, also matted on its inner surface a nd sealed to the fibre. The applicator provided a homogeneous light intensi ty 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 di ffusing tip with a Ringmode(R)-ITT applicator in order to find optimal lase r parameters and damage thresholds. The lesions were investigated using mac roscopic 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 l imit at 5 W and 12 min exposure. Comparing various exposure times showed th at 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 lesi ons were not significantly different for both applicators when the same las er parameters were applied. On the other hand, the new diffusing tip had a higher damage threshold and was therefore capable of producing maximal coag ulation volumes of up to 7.9 +/- 0.5 cm(3) at 5 W and 20 min. The experimen ts 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 huma n liver metastases in a single laser session.