Hyperthermia response and thermotolerance capacity of an experimental rat tumour with occluded blood flow

Thermotolerance in vivo was investigated using the rat fibrosarcoma SSBla. Hyperthermia was administered using water-bath heating, with the tumour blood supply occluded by clamping during the heating procedure. Single-dose heat treatments (10-60 min at 43.5 degrees C) yielded linear dose-response curves, with response evaluated as tumour re-growth delay. In thermotolerance studies split-dose treatments were given in which a single 'priming' treatment of 30 min at 43.5 degrees C was followed 24 or 48 hr later by a variable treatment (10-90 min), again at 43.5 degrees C. Split-dose responses produced generally less uniform results, though the dose-response curves were still approximately linear. Comparison of the slopes of the dose-response curves for single-dose and split-dose treatments gave a 'thermotolerance ratio' (TTR) of 4.09 and 3.45 at 24 and 48-hr intervals respectively. Data analysis using Monte Carlo simulation techniques also suggests that the distribution of tumour sensitivities to a second heat treatment may be considerably broader than the distribution of sensitivities to a first treatment. Uniformity of tumour response to a single heat treatment may therefore conceal a spectrum of capacities for development of thermotolerance amongst individual tumours.