Skin and other reactions to radiotherapy--clinical presentation and radiobiology of skin reactions.

The skin represented the dose-limiting organ in radiotherapy over long periods of time. In the first third of the 20th century, radiotherapy was associated with deposition of significant radiation doses in the superficial compartments of the skin. Therefore, all major radiobiological principles, such as effects of fractionation on radiation sensitivity or volume/area effects, were initially based on observations in epidermal radiation reactions. The development of radiation sources producing mega-voltage X-rays resulted in translocation of dose maxima into the subcutaneous soft tissue. With this, and with the introduction of multiple-field irradiation techniques, severe radiation effects in the skin were almost completely prevented. However, skin reactions are still relevant to critical skin areas, such as intertriginous regions. Also, the treatment of skin tumours, which requires high skin doses, is associated with substantial skin effects. Combinations of radiotherapy, e.g. with chemotherapy or UV exposure, can significantly aggravate skin effects. Moreover, accidental radiation exposure is frequently associated with significant skin doses. Therefore, early and late reactions of the skin must still be considered clinically relevant.