PERFUSION AND THERMAL FIELD DURING HYPERTHERMIA - EXPERIMENTAL MEASUREMENTS AND MODELING IN RECURRENT BREAST-CANCER

Recurrences of malignant tumours in the chest wall are proposed as a v aluable model of tissue mainly perfused by small size vessels (the so- called 'phase III' vessels). Invasive thermal measurements have been p erformed on two patients affected by cutaneous metastasis of malignant tumours during hyperthermic sessions. Thermal probes were inserted in to catheters implanted into the tissue at different depths. In one of the catheters a probe connected with laser-Doppler equipment was inser ted to assess blood perfusion in the tumour periphery. The perfusion w as monitored throughout the sessions, and a noticeable temporal variab ility was observed. The effect of the perfusion on the thermal map in the tissue was evaluated locally and the 'effective conductivity' of t he perfused tissue was estimated by means of the numerical integration of the 'bio-heat' equation. The tumour temperature, at the site where the perfusion probe is located, can be predicted by the numerical mod el provided two free parameters, alpha and beta, are evaluated with a fitting procedure. alpha is related to the effective conductivity and beta to the SAR term of the bio-heat equation. The model aimed at esti mating the 'effective conductivity' K-eff of the perfused tissue, and average values of K-eff of 0.27 +/- 0.03 W m(-1) degrees C-1 in Patien t 1 and of 0.665 +/- 0.005 W m(-1) degrees C-1 in Patient 2 were obtai ned throughout the treatment. However, when the average temperature in a larger tumour volume is to be predicted but only a single, 'local' measurement of the perfusion is available and is assumed to be represe ntative for the whole region, the model results are far less satisfact ory. This is probably due to the fact that changes of blood perfusion throughout hyperthermic sessions occur to different extents within the tumour volume, and the differences in perfusion cannot be ignored. Th e above result suggests that, in addition to the 'temperature map', al so a 'perfusion map' within the heated volume should be monitored rout inely throughout hyperthermic sessions.