Principles of Radiation Therapy

TOPIC: PRINCIPLES OF RADIATION THERAPY(TIME, DISTANCE AND SHIELDING)

Radiation Therapy uses ionizing radiation to kill or limit the growth of cancer cells, may be internal or external. It not only injures the cell membrane but destroys or alters DNA so that the cells cannot reproduce. Like chemotherapy, effect cannot be limited to cancer cells only; all exposed cells, including normal ones, will be injured, causing side effects. Localized effects are related to area of body being treated; generalized effects may be related to cellular breakdown products.

Factors Controlling Exposure

A.   Half-life: time required for half of radioactive atoms to decay

1.    Each radioisotope has a different half-life.

2.    At the end of the half-life, the danger from exposure decreases.

B.    Time: the shorter the duration, the less the exposure

C.   Distance: the greater the distance from the radiation source the less the exposure

D.   Shielding: all radiation can be blocked; rubber gloves stop alpha and usually beta rays; thick lead or concrete stops gamma rays

E.    These factors affect health care worker’s exposure as well as client’s.

1.    Health care worker at greater risk from internal than external sources

a.    Limit visitors to 30 mins. per day; visitors should be at least 6 feet from the source.

2.    Film badge can measure the amount of exposure received

3.    No pregnant nurses or visitors permitted near radiation source