Critical temperature and heating time for coagulation damage: Implicationsfor interstitial laser coagulation (ILC) of tumors

Background: Interstitial laser coagulation (ILC) is a method of local tissu e destruction for solid tumors such as irresectable hepatic metastases from colorectal cancer. With the availability of new magnetic resonance (MR) te chniques, which allow real time tissue temperature mapping, it is essential to know the critical temperature and exposure times leading to cell death. Materials and Methods/Study Design: Samples (8 mm(3)) of solid rat tumor (C C-531, syngenic to the WAG/Rij rat strain), were warmed in tubes for four d ifferent temperatures (40, 50, 60 or 80 degrees C) and four different expos ure times (3, 6, 12, or 24 minutes). Combinations were replicated in five-f old. Cell viability was assessed with three methods: Trypan blue exclusion test in collagenase/dispase dissociated samples, NADH activity in snap froz en samples and outgrowth for 2 weeks under the renal capsule of WAG/Rij rat s. Results: Results of the three methods revealed that viability was not affec ted with heating at 40 and 50 degrees C except for 24 minutes at 50 degrees C. At higher temperatures cell death occurred at all exposure times. Conclusion: The temperature range resulting in sufficient tissue coagulatio n for cell death is between 50 degrees C and 60 degrees C for a short durat ion (<3 minutes). These data can be used to achieve complete tumor destruct ion and minimal surrounding tissue damage during real-time MR-controlled IL C. (C) 1999 Wiley-Liss, Inc.