cardinal principal of radiation protection

Radiology is designed to reduce radiation exposure of all health physics activity patients and personnel. Time, Distance and Shielding for Nuclear Activity Developed three cardinal principals, which were found equally useful for diagnostic radiology. Radiation exposure can be worked out using these cardinal principal.

MINIMIZE TIME

The dose of any person is directly related to their exposure time. If someone's exposure time is doubled, then his exposure will also be doubled.

Exposure time is kept low during the radiograph, which reduces the motion blur in the X-ray film. In fluoroscopy, the exposure time should be reduced, so that the patient and the personnel reduce the radiation dose. This is the part of radiation protection that is not directly connected to the radiation technologist. For this the radiologist is trained to turn off the foot switch of fluoroscopy as a sequence instead of constantly taking medicines. This reduces radiation dose. Pulsed progressive fluoroscopy can reduce patient dose by 0.1 times.

MAXIMIZE DISTANCE

 Increasing the distance between radiation source and patient reduces radiation exposure rapidly. This dose reduction is calculated from the inverse square law. Most radiation sources are point sources such as X-ray tubes. In a radiograph, the distance between the patient and radiation source is usually fixed and the radiation technician stands behind the protective lead barrier.

MAXIMIZE SHIELDING

By shielding between exposed person and radiation source from radiation, radiation dose can be reduced drastically, such as protective lead barrier. In diagnostic radiology, shielding is made of lead or lead aquilant material. How much radiation shielding material prevents radiation can be detected from either the half value layer (HVL) or the tenth value thickness (TVT).

HVL

The amount of shielding material that reduces the radiation dose by half. 

Another example of the use of shielding material in radiology is protective apparel. Protective aprons generally contain 0.5mm Pb. This is approximately equal to 2HVL by which occupational exposure should be brought down to 25%.