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6 Hyperthermia in Combination with Radiation in the Treatment of Cancers

Mitsuyuki Abe, Masahiro Hiraoka


Hyperthermia has been clinically investigated over the past two decades as a treatment modality for human malignant tumors. The biological rationale for the use of hyperthermia in the treatment of cancer is based on the following experimental findings:Heat kills cells exponentially as a function of time at temperatures above 42°C.

Hypoxic cells are at least as sensitive to heat as oxic cells.

Tumors may contain cells with low pH and with nutrient deficiency, which make cells more sensitive to heat.

Tumors tend to become hotter than surrounding normal tissues during hyperthermia because of a more sluggish blood supply and a lesser capacity for increased blood flow upon heating.

The vasculature in tumors is damaged at lower temperatures than that in normal tissues, resulting preferentially in the secondary death of tumor cells and making the tumor temperature rise more easily upon the second heating.

Cells in the late S phase, known to be radioresistant, are sensitive to heat.

Under some conditions, heat interacts synergistically with radiation, partially as a result of inhibition of sublethal or potentially lethal damage repair.

Heat may potentiate the cytotoxic effects of some kinds of chemotherapeutic drugs either by increasing drug uptake or by enhancing sensitivity to the drug.

On the other hand, there are several problems in thermotherapy. The first is thermotolerance, which is defined as the development of resistance of cells to subsequent heat by prior heating. At lower temperatures of around 42°C, thermotolerance...

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