The Rationale for Combining Hypofractionated Radiation and Hyperthermia.

The conventional radiation treatment of cancer patients has typically involved a large number of daily treatments with relatively low doses of radiation. However, improved technology has now resulted in the increased use of fewer radiation fractions at a high dose per fraction. This latter approach is often referred to as hypofractionated irradiation. While conventional radiation typically kills tumor cells through the production of DNA damage, treatments with higher doses per fraction have been suggested to also kill cells via the induction of vascular damage. Such vascular effects will also increase the level of adverse microenvironmental conditions, such as hypoxia and acidity, that already exist in tumors. Cells existing in these adverse microenvironmental conditions are resistant to radiation but actually sensitive to hyperthermia (heating at 40-45 °C) treatment. This suggests that the combination of hypofractionated radiation and heat may be a viable treatment approach. While there are preliminary pre-clinical and even clinical studies investigating this option, there are actually no data on the optimal application for the greatest therapeutic benefit. In this critical review, we will present the rationale for combining hypofractionated radiation with hyperthermia and discuss what has been done and what should be done to establish this combination as an effective cancer therapy option.