Acute and late effects of radiation

Acute effects of radiation comprise the dose-limiting normal tissue reactions during a course of radiotherapy and involve mainly the mucosa and the haemopoietic system. Although initial cell loss may be partly through apoptosis, the predominant effect is loss of reproductive capacity, interfering with the replacement of lost cells. Thus, tissues with fast normal cellular turnover (epithelia of skin and gut, bone marrow) display effects of irradiation earliest.

Timing of radiation effects also depends on rate of dose administration. After a single dose of 10 Gy, the mucosal lining of the intestinal tract is depleted in a few days, while it may take several weeks during a fractionated course of radiotherapy with daily doses of 2 Gy.

The speed of recovery of acute reaction depends on the level of stem cell depletion, and varies from a few days to several months. If the number of surviving stem cells is too low, severe epithelial damage may persist as a chronic ulcer.

Late effects occur predominantly in slowly proliferating tissues (such as the lung, kidney, heart, liver, and the central nervous system) but are not necessarily restricted to these slowly renewing cell systems (e.g. in the skin, in addition to the acute epidermal reactions, late changes such as fibrosis, atrophy, or telangiectasia can develop up to several years later).

The distinction between acute and late effects has important clinical implications. Since acute reactions are usually observed during the course of a conventionally fractionated radiotherapy schedule (1.8-2 Gy per fraction, five times a week), it is possible to adjust the dose in the event of unexpectedly severe reactions, allowing a sufficient number of stem cells to survive. Surviving stem cells will repopulate and restore the integrity of the rapidly proliferating tissue. When overall treatment time is reduced, the acute reactions may not reach maximal intensity until after completion of treatment. This precludes adjustment of the dose regimen to the severity of reactions. If intensive fractionation schedules reduce the number of surviving stem cells to below the level needed for effective tissue restoration, acute reactions may persist as chronic injury, called consequential late complications.

By definition, late radiation reactions are not apparent until a considerable time after irradiation and these are by no means always predicted by the severity of the acute reaction. Although the total dose of radiation is most important, another major determinant of late radiation effect is the dose of radiation per fraction of treatment.

The time elapsing between radiation and the clinical appearance of a radiation-induced lesion has basically no relationship with the radiosensitivity or tolerance of the relevant normal tissue. Some acutely responding tissues such as the skin and mucosa are relatively resistant, in contrast to the highly radiosensitive haemopoietic tissues and germ cells. Conversely, typically late responding tissues like the lung and kidney are among the most sensitive, while the brain is in the more resistant part of the spectrum.

How To Deal With Rosacea and Eczema

How To Deal With Rosacea and Eczema

Rosacea and Eczema are two skin conditions that are fairly commonly found throughout the world. Each of them is characterized by different features, and can be both discomfiting as well as result in undesirable appearance features. In a nutshell, theyre problems that many would want to deal with.

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