The skin-sparing capabilities of megavoltage, high-energy equipment, and increasingly sophisticated treatment planning methods have reduced the incidence of severe skin complications. However, certain acute and late side effects of radiation occur and, in some instances, are expected and unavoidable as the radiation must enter, exit, or be deposited near the skin to reach the target volume. Skin cells, because they originate from a rapidly reproducing differentiated stem cell, are relatively radiosensitive. Skin reactions occur as a result of inflammatory response and the depletion of actively proliferating cells in a renewing cell population. Archambeau et al.1 describe the early and late changes as dependent on the dose and are a reflection of changes in the cellular components of the epidermis, dermis, and vasculature.
Normal skin response to radiation depends on numerous patient- and treatment-related factors. Radiation factors include the beam type and energy, use of tangent fields, use of tissue equivalent (bolus) material, weekly dose rate, accelerated fractionation, and field size. Patient factors include skin folds in the treatment volume, nutritional status, comorbidities, and the use of irritants to irradiated skin.2 Individual differences in radiosensitivity and concurrent chemotherapy also influence skin tissue response to irradiation.24
There is a dose-dependent loss of cells from irradiation in the epidermis, dermis, and microvasculature endothelium.3 Dose above the tolerance of the tissue may eventually result in necrosis. Acute skin reactions are a reflection of inflammatory response and the inability of dermal and epidermal cells to keep up with the accelerated loss caused by radiation.
Skin changes from radiation are apparent within days of the first exposure. Acute effects of radiation are those that occur during and within 6 weeks of exposure while late effects occur a few months to years after exposure to radiation. Acute effects ofradiation are usually considered temporary, as the normal cells are often capable of repair. Late radiation effects are usually permanent and may become more severe as time passes. The severity of acute and late effects is dependent on the dose of radiation, time over which the total dose was delivered and the volume oftissue radiated. The presence and severity of acute radiation skin reactions may predict late effects of radiation. Late skin effects such as tissue fibrosis or necrosis can occur independent of acute reactions. Side effects of radiation on the skin, both acute and late, are local and confined to the actual tissue irradiated.
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