4.2 Patient Radiation Dose Management

Patient radiation dose is expressed

• entrance skin exposure (ESE)

• Mean marrow dose ( MMD)

• Genetically Significant Dose (GSD)

Entrance skin exposure (ESE) is used

most often because its the easiest to measure

Entrance Skin Exposure (ESE)

• referred to as “patient radiation dose”

• easy to measure -usually performed by physicists

• reasonably accurate

• TLDS & OSLs are most often used with ESE

• the average fluoroscopic exam estimates ESE of 40 mGyt/min

Patient dose from diagnostic x-rays is most often reported in _____________________

a. bone marrow dose

b.gonadal dose

c. entrance skin dose

d. reproductive organ dose

c. entrance skin dose

Nomogram curve

• exposure multiplied by mAs value to approx patient exposure

• Dose= exposure (mAs)

Mean marrow dose (MMD)

• the average radiation dose to the entire active bone marrow

• mean marrow dose average is 1 mGy t/year

• hematologic effects are rarely experienced in diagnostic radiology

• mean marrow dose is used to estimate, on a population basis, the risk of one late effect of radiation -leukemia

Distribution of bone marrow in adults

head

10%

Distribution of bone marrow in adults

t vertebrae

13%

Distribution of bone marrow in adults

upper limb girdle

8%

Distribution of bone marrow in adults

L-vertebrae

sacrum

ribs

11%

Distribution of bone marrow in adults

sternum

3%

Distribution of bone marrow in adults

lower limb girdle

29%

Distribution of bone marrow in adults

c-vertebrae

4%

Genetically significant dose (GSD)

• measurements and estimates of gonadal dose is important because of the suspected genetic effects of radiation

• the gsd is the gonadal dose that, if received by every member of the population, would produce the total genetic effect on the population as the sum of the individual doses actually received

• the gsd is estimated only through large-scale studies

• the gsd is estimated only through large scale studies

The GSD for the US is

0.2 mGyt/yr

DAP is a quantity that reflects not only the patient radiation dose,

but also the amount of tissue irradiated

may be a better indicator of risk rather than dose

DAP increases with increased

radiation field size (more tissue irradiated)

An estimation of patient dose is reported as ________________________________

a. entrance skin exposure

b. bone marrow dose

c. gonadal dose

d. ESE. bone marrow dose and gonadal dose

d. ESE, bone marrow dose and gonadal dose

An ESE of 40 mGy a is the average

dose for a fluoroscopic exam

ESE above 15 Gyt is a

sentinel event

skin damage usually follows a sentinel event

A sentinel event is an unexpected occurance

involving death or serious physical or psychological injury , or the risk thereof serious injury specifically includes loss of limb or function

Effective dose is the patient radiation dose metric that is used to

estimate stochastic radiation responses

Effective dose formula

E = (Di Wt)

Repeat examinations are estimated to be as high as

10% of all examinations

Lumbar & thoracic spine, chest and abdomen are the

most repeated examinations

High kVp,

low mAs

Patient dose can be reduced by using

___________________

a. increased distance

b. decreased distance

c. higher kVp

d. repeating exposures

c. higher kVp

Specific area shielding devices are usually formed with

0.5 mm lead contact shield

Radiologic considerations

• biologic response is time and dose related

• fetus is most sensitive before birth

• general rule, the higher the dose the more severe the response

During the first 2 weeks of pregnancy, if irradiated

high enough, the response would be reabsorption of the embryo

2-12 weeks - organogenesis- major organs are developing, may produce

congenital abnormalities

Early organogenesis-

most likely skeletal abnormalities

require doses greater than 250mGyt

Late organogenesis-

most likely neurological abnormalities

require doses greater than 250mGyt

Responses after organogenesis most likely

malignant disease during childhood

require doses greater than 250mGyt

In utero irradiation of 2 Gyt will produce

skeletal neurological, or malignant effects

Spontaneous abortion during first 2 weeks is unlikely to

occur with doses less than 250 mGyt

The period of major organogenesis is during the ______________ of pregnancy

a. first 2 weeks

b. 2nd to 10th wk

c. 2nd trimester

d. 3rd trimester

e. first trimester

e. first trimester

10 day rule

irradiation should be restricted to the first 10 days of the menstrual cycle, or first 10 days following the onset of menstruation

28 day rule

radiological examinations, only if justified, can be carried throughout the cycle until a period is missed

Damage to the fetus is unlikely at doses below

250 mGyt

Below 100

no abortion

above 250

justification for therapeutic abortion

Fetal doses rarely exceed

50 mGyt after a series of xray examinations

Occupational exposures

effective dose

annual:

cumulative:

annual: 50 mSv

cumulative: 10 mSv x age

Occupational exposures

equivalent annual dose for tissue and organs

lens of the eye:

thyroid,skin,hands, and feet:

lens of the eye: 150 mSv

thyroid, skin, hands, and feet: 500 mSv

Public exposures (annual)

effective dose, frequent exposure:

equivalent dose for tissues and organs

lens of eye:

skin, hands, and feet:

lens of eye: 15 mSv

skin, hands, and feet: 50 mSv

Education and training exposures (annual)

effective dose:

equivalent dose for tissues and organs

lens of eye:

skin, hands, and feet:

effective dose: 1 mSv

lens of eye: 15 mSv

skin, hands, and feet: 50 mSv

Embryo- fetus exposures

total equivalent dose ( complete gestation) :

equivalent dose in 1 month:

total equivalent dose ( complete gestation) : 5 mSv

equivalent dose in 1 month: 0.5 mSv

Negligible individual dose (annual):

0.01 mSv