Interstitial laser thermotherapy of adenocarcinoma transplanted into rat liver

Objective: To examine the effect of different temperatures and exposure times in interstitial laser thermotherapy. Design: Controlled laboratory study. Setting: University hospital, Sweden. Material: 48 male Wistar FU rats with dimethylhydrazine-induced adenocarcinoma transplanted into the liver. Intervention: Treatment was given with an Nd:YAG laser and a feedback system for temperature regulation. Light was delivered into the centre of the turnout and the feedback thermistor probe was placed 3 mm from the tumour margin. Rats were treated at steady-state temperatures at the feedback thermistor of 43, 46, or 50°C for 30 minutes, and at a steady-state temperature of 46°C at the feedback thermistor also for 10 and 20 minutes. Main outcome measurement: Tumour control as assessed 6 days after treatment using light microscopical examination including immunohistochemical determination of bromodeoxyuridine (BrdU) incorporation into DNA as a measure of cell viability. Results: Complete tumour necrosis was achieved in all rats treated for 30 minutes, in 6/8 rats treated for 10 minutes and in 6/8 rats treated for 20 minutes at 46°C. During steady-state thermotherapy, temperatures at the tumour margin were about 11°higher than at the feedback thermistor (range 54-61°C). The surrounding liver tissue also became necrotic so that the total necrosis volume exceeded the pretreatment tumour volume. Conclusion: Interstitial laser thermotherapy at temperatures ranging from 54-61°C at the tumour margin ensures total necrosis of a transplanted rat liver carcinoma provided that treatment is given for 30 minutes