Effect of vascular occlusion on tumour temperatures during superficial hyperthermia

Tumour temperature heterogeneity during hyperthermia has been attributed to irregular tumour vascular perfusion. We have compared temperature distributions in human tumours subjected to superficial hyperthermia under conditions of normal and occluded blood flow. Three patients with recurrent malignant melanoma on the leg were treated with radiation followed by hyperthermia 60-90 min later on days 1, 8 and 22. Heating (15-30 min) with normal blood flow was followed by 15 min of heating with tourniquet occlusion, although the tourniquet had to be intermittently released when the patients complained of discomfort. Hyperthermia was delivered using either a 1.4 MHz ultrasound or 915 MHz microwave applicator. Temperatures were monitored using superficial and interstitial thermometers in tumour and normal tissues. When the tourniquet was applied, the amount of power required to maintain peak temperatures was decreased by a factor of 3-10. With normal blood flow, there was a significant degree of temperature heterogeneity within the treatment volume, both within normal and tumour tissues, which improved with tourniquet application. The T90 and T50 indices increased both in normal tissues and tumour following the tourniquet occlusion, with the temperature increments being greater for normal tissues. Temperatures at depth were increased despite the reduction in applied power and the temperature profiles were smoother when the tourniquet was applied. No cutaneous, vascular or neuromuscular side effects were observed amongst these three subjects either acutely or at 1 month follow-up. These studies demonstrate directly that the temperature heterogeneity which exists in human tumours subjected to external heating can be reduced by occluding the blood supply.