Therapeutic Benefit from Combined Heat and Radiation

Abstract

The response of both tumours and normal tissues to heat, X-rays or a combination of the two is complex. Both agents can act directly by causing cell death or the loss of proliferative capacity. In addition, both agents can act indirectly, by damaging the vasculature and thereby leading to ischaemic cell death as blood vessels collapse or are occluded by thrombi (Fig. 1). When the two agents are combined there may be a synergism, antagonism or sensitisation of the action of either agent by the other. The response to both agents can be modulated by physiological changes, particularly by oxygenation or acidity changes that may follow from alterations of the patterns of blood flow. If heat and X-rays are to be used clinically in a way that will be safe and will give the maximum therapeutic advantage, it is important to be able to understand and separate these different elements in the response. It is possible to go some way towards this by studying the time course of the response of tumours and normal tissues to each agent separately and to the combination.