Chapter 11 Review

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Management of Patient Radiation Dose During Diagnostic X-Ray Procedures

gonadal shielding devices

-used when gonads are located within 5 cm of the primary beam

female shielding

-female organs receive 3 times more radiation in a pelvis exam than the male
-flat contact shield- reduce dose 50%

male shielding

-shaped contact shield- reduce exposure by 90-95%

four types of gonadal shields

-flat contact
-shadow shield
-shaped contact
-clear lead

flat contact shields

-1 mm lead
-most effective in recumbent position

shadow shields

-cannot be used in fluoro because no localizing light is used in fluoro

genetically significant dose

-for US population is .20 mSv (20 mrem)

proper exposure factors

-penetration
-density
-contrast
-type of generator
-balance of density and contrast

air-gap technique

-alternative to grid use
-chest, swimmers, x-table cspine
-IR is 6-10 inches from pt, and tube is 10-12 feet from IR
-most effective below 90kVp

non-essential radiologic exams

-exams practiced in the past
-pre-employment physical screenings
-admission chest xrays
-pre-op chest xrays
-l spine exam as pre-employment screening
-whole body CT

patient dose

-expressed in 4 ways: entrance skin exposure, skin dose, gonadal dose, bone marrow dose

entrance skin exposure

-easiest to obtain
-measure distance between tube and pt
-tape a TLD to pt's skin

gonadal dose

-insignificant in a single human
-when applied to entire population, dose becomes important

genetically significant dose

-dose equivalent to the reproductive organs that would have an identical genetic injury to the total population as would an individual of the population
-US Public Health Service estimates the GSSD for the US pop is about .20mSv (20 mrem)

bone marrow dose

-can only be estimated
-can provide a measurement of pt absorbed dose

irradiation during unknown pregnancy

-if pt expresses concern to OBGYN about rad exposure:
-OBGYN notifies imaging dept
-imaging dept review exam history of the date the pt was in the dept
-form is completed listing exams
-RSO calculates EqD to embryo/fetus

mammo

-FDA regulations state that the maximal dose to the glandular tissue of a 4.5 cm compressed breast using screen-film should not exceed 3mGy (300mrad) per view

mammo units

-capable of producing optimal images with an avg glandular dose of less than 2mGy (200mrad)

when is mammo necessary?

-controversy; organizations felt it is better to do baseline images at a young age to see how the tissue changes)
-baseline images done when the breast tissue is still young (35-39 yrs)
-screenings every year beginning 40-49 yrs
-women over 50 should have mammo screenings every year

CT

-2 concerns regarding pt dose and CT scans
1. skin dose
2. dose distribution during the scan
-skin dose is 100 times higher in xray
-CT dose is more uniform throughout the pt

10-day rule

-1970, the IRCP recommended the 10-day rule:
-no radiation exposure 10 days after the onset of a menstrual cycle
-this made scheduling exams difficult
-now the rule is obsolete
-ACR feels abdominal exams that have been ordered should not be selectively scheduled

doses

-most rad exams produce doses less than 1 rad
-pregnant Hiroshima bombing survivors did not have any birth defects in their children if the dose was below 20 rad
-NCRP states that doses below 5 rad are negligible
-doses above 15 rad can cause birth defects

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