Fluoroscopic doses

Factors affecting patient dose

Small intensifier field size have higher relative patient entrance doses

1. Irradiate patient volume

Scatter dose rate is higher when field size increases

1. Effective use of articulated shielding and or/protection goggles

Protection tools

Screen and goggles

Curtain

Thyroid shield

Personal dosimetry

Normal occupational dose limits apply; i.e.:

• A limit on effective dose of 20 mSv/year, averaged over 5 years
  (i.e., a limit of 100 mSv in 5 years) with the further provision that in any single year:
• The effective dose should not exceed 50 mSv, and
• The equivalent dose should not exceed
  • 150 mSv for the lens of the eye,
  • 500 mSv for the skin (average dose over 1 cm² of the most highly irradiated area of the skin) and
  • 500 mSv for the hands and feet
• PATIENT DOSE WILL INCREASE IF :
  • THE SOURCE-TO-SKIN DISTANCE IS SHORT
  • THE PATIENT-IMAGE INTENSIFIER DISTANCE IS LARGE

Factors affecting staff dose

The majority of photons reaching the patient are scattered or absorbed, i.e. the source of radiation to the staff is mostly scatter from the irradiated patient.

Relative position of staff 

The relative position (including height) of staff with respect to the patient (source). Scattered radiation obeys the inverse square law, hence the greater the distance from the patient improves staff safety.

The inverse square law describes the principle of dose reduction as the distance from the source increases, assuming a point source of radiation.

Therefore, the dose is proportional to the inverse of the square of the radius. Thus if you double the distance you reduce the dose by a factor of four.

A = 4πr2

Furthermore the scatter dose rate is higher near the area where the x-ray beam entering the patient due to the angle dependence of scatter. i.e. scattered dose is highest at the x-ray tube side

X-ray tube position

Tube undercouch position reduces high dose rates to the operators eye lens

kV, mA and time (number and characteristics of pulses)

High dose rate mode increases the dose by a factor of 2 or more

Use of the antiscatter grid increases patient entrance dose by factor of 2 of to 6