CVT 102

TimeDistanceShielding

Establish standard protocols (including limits on fluoroscopic exposure time)

Know dose rates of equipment Assess procedure protocol for potential

radiation injury Modify procedure to limit cumulative

radiation dose Medical physicist should help implement

principles

Pulsed fluoroscopy Low tube current

◦ Less radiation, less exposure Higher kVp

–Higher voltage causes radiation to go through patient; less absorption; less skin dose

–Balance contrast and distance

Distance◦ Keep image intensifier as close to patient as

possible◦ Increase distance from x-ray tube to patient

Field of view ◦ Collimate to reduce field of view to region of

interest Limit use of magnification techniques

◦ Magnification increases patient dose

Last image hold ◦ Displays last image captured on monitor

Beam on-time ◦ Intermittent fluoroscopy ◦ 5 minute reset timer

Rotate fluoroscope around a center (do obliques and laterals)

Keep other body parts (arms, breasts) out of the x-ray field

Maintain logs to track trends in exposure and analyze problems

Inverse square law ◦ The exposure is inversely proportional to the

square of the distance from the source of radiation (scattered radiation from the patient).

◦ To minimize exposure, stand as far away from the patient as practical

Do not put any part of your body in the primary beam

Distance is the most important method of protection

Reduce the time you are exposed to radiation ◦ Fluoroscopist should use intermittent fluoroscopy ◦ Minimize beam-on time

5 minute audible timer ◦ High dose fluoroscopy requires audible signal

while on ◦ Use last image hold ◦ Use pulsed technique

Lead aprons (.5mm Pb equivalent) Thyroid collars Lead gloves Leaded glasses

Dose limits ◦ Whole body – 5,000 mrem/year (50 mSv) ◦ Skin, hands, feet – 50,000 mrem/year (500 mSv) ◦ Cumulative – 1,000 mrem (10 mSv) X age in years

Monitors worn on collar outside the protective aprons

Interventional personnel use additional monitor at waist level under the lead apron

The National Council on Radiation Protection and Measurements recommends using the ALARA (As Low As Reasonably Achievable) principle ◦ Try to keep exposure to less than 1/10

recommended dose limit

Exposure levels—CR vertical, PA projection, intensifier on top.*†

(Least exposure to operator)

Vertical orientation with tube on top (increases exposure to head and neck of operator —NOT recommended.

operation

Exposure levels—CR 30° from vertical. *†(CR angle increases exposure to operator)

Exposure patterns and levels—CR horizontal.*†(Least exposure at intensifier side)