Low power interstitial Nd YAG laser photocoagulation: studies in a transplantable fibrosarcoma.

The effects of interstitial delivery of low power (1.2-2 W), long exposure (600-1200 s) Nd YAG laser light on a transplantable fibrosarcoma in rats have been studied. Three cohorts of ten animals were treated either by 1.2 W for 600 s, 1.2 W for 1200 s or 2 W for 600 s to each tumour nodule. An additional untreated cohort served as controls and a further cohort was treated by radical surgical resection. A partial response as evidenced by ulceration was seen in all laser-treated tumours. In the cohort treated by 2 W for 600 s there was complete loss of palpable tumour, and in five out of the ten animals there was no evidence of local recurrence following a prolonged period of observation. Three of these eventually died from metastatic disease and two were cured. There was a significant prolongation of survival in this cohort compared with the controls (median 70 days versus 30 days, P less than 0.05), but not in any of the other cohorts. Histological assessment of tumours 2 days after laser treatment showed a central area of degeneration with shrunken and densely staining nuclei and disorganized cytoplasm, the boundary between the degenerate zone and surrounding viable tumour being well defined. The technique might be used to induce necrosis of intrahepatic and other solid organ tumours.