Clinical use of thermal enhancement and therapeutic gain for hyperthermia combined with radiation or drugs.

Values for thermal enhancement and therapeutic gain are useful for deciding future directions of hyperthermia combined with other cancer therapy modalities. Evidence of thermal enhancement of effects on normal tissues is important as it indicates the need for dose modification. Specific values cannot be used generally to determine the degree of dose modification for clinical applications. A range of values accounting for many variables, including method of dose delivery for heat and the other modalities and knowledge of the normal tissues at risk, would be required for such specific application. There is frequently hyperthermic enhancement of radiation damage to acutely responding tissues. That may be avoided if tumors can be selectively heated, but extensive temperature monitoring is necessary to avoid hot spots. Irradiation and heating of spontaneous canine tumors resulted in an increased probability for tumor control with no apparent increase in late complications. Human clinical studies have shown that, with care, tumor response can be enhanced without significantly increasing normal tissue damage and that a therapeutic gain can be achieved. Caution must be exercised because, with few exceptions, follow-up was not long, and the tissues at risk were limited. Most human studies have been of relatively superficial tumors of small volume. Little information is available on whole-body or regional hyperthermia for assessment of thermal enhancement or therapeutic gain. Also, there is little information about chemotherapy combined with heat, although studies of heat with perfusion chemotherapy for malignant melanomas of the extremity have shown significantly increased survival rates.