Unit 3 Exam

Based on Study Guide

Control area

An area with trained x-ray personnel and wear dosimeters. Occupancy factor of 1

Uncontrolled area

Non-radiation personnel or the general public

What is the maximum annual exposure rate allowed for the controlled area?

50 mSv/year = 1 mSv/week

What is the maximum annual exposure rate allowed for the uncontrolled area?

1 mSv/year = 0.02 mSv/week

What percentage accuracy should the SID indicator be of the indicated SID?

Within (+/ -) 2%

What about the light-field radiation field congruency?

Within (+/ -) 2% of SID

NCRP minimal total filtration requirements based on report #102: below 50 kVp:

.5 mm Pb

NCRP minimal total filtration requirements based on report #102: 50-70 kVp:

1.5 mm Pb

NCRP minimal total filtration requirements based on report #102: above 70 kVp:

2.5 mm Pb

What are examples of a primary protective barriers?

Radiographic room walls, floor, and exposure room door

What are examples of secondary protective barriers?

Control booth barrier, many walls, x-ray tube housing, lead aprons, gloves, and portable barriers

What are the rules for the primary barriers?

1.6 mm lead. Lead bonded to sheet rock or wood paneling is used most often. 4 inches of masonry is equivalent to 1/16 of lead. Concrete, concrete block, or brick may be used instead.

What are the rules for the secondary barriers?

All lead aprons, gonadal shielding, and gloves must be 0.25 mm lead. Thyroid shields must be .5 mm lead equivalent. Portion of wall above 7 feet must be 0.8 mm lead

What is the relationship between SSD and ESE?

If SSD is increased, the ESE decreases (inverse)

Film badge

As low as 0.1 mSv. Reading of “M”

TDL

0.05 mSv (low exposure limit). Worn for 3 months, measured visible light is proportional to the absorbed radiation dose

OSL

Sensitive to .01 mSv. Useful for pregnant workers. Reads “M”. Dose measurement range from 0.01 mSv - 10 mSv

In radiography of the abdomen, which of the following techniques provide the most patient ESE?

8 mR/mAs and 40 mAs = 320 mR

If you are a pregnant female radiographer who has declared your pregnancy in writing. What benefits/protection can you be provided?

• RSO should review exposure history

• Waist level (fetal-badge) dosimeter is issues and read on a monthly basis (entire pregnancy is 5 mSv)

• Assigned a wrap around lead apron

• Pregnant radiographer will not be forced to leave the department because of declaring pregnancy in writing

• Under no circumstance should termination or involuntary leave of absence occur

What are some of the ways we can help prevent unnecessary radiation exposure for our patients that might be pregnant?

• 10 day rule

• Elective booking

• Patient questionnaire/consent form

• Radiation pregnancy caution signs

• Shielding and no repeats

NCRP #116 dose limit recommendations: Annual occupational exposures:

50 mSv

NCRP #116 dose limit recommendations: cumulative occupational exposures:

10 mSv x age

NCRP #116 dose limit recommendations: occupational lens of the eye for equivalent annual dose for tissues and organs:

150 mSv

NCRP #116 dose limit recommendations: occupational thyroid, skin, hands, and feet for equivalent annual dose for tissues and organs:

500 mSv

NCRP #116 dose limit recommendations: public exposures frequent exposure:

1 mSv

NCRP #116 dose limit recommendations: public exposures for infrequent exposure:

5 mSv

NCRP #116 dose limit recommendations: public exposures for lens of the eye

15 mSv

NCRP #116 dose limit recommendations: public exposures for skin, hands, and feet:

50 mSv

NCRP #116 dose limit recommendations: education and training exposures effective dose:

1 mSv

NCRP #116 dose limit recommendations: lens of they eye for education and training exposures:

15 mSv

NCRP #116 dose limit recommendations: skin, hands, and feet for education and training exposures:

50 mSv

NCRP #116 dose limit recommendations: embryo fetus exposures, total equivalent dose (entire gestation period):

5 mSv

NCRP #116 dose limit recommendations: embryo fetus exposures, equivalent dose in 1 month:

0.5 mSv

NCRP #116 dose limit recommendations: students younger than 18 years of age:

1 mSv

What are the factors to conciser when calculating the required protective barrier thickness of an x-ray room? (DOCWUK)

Distance, occupancy, control, workload, use factor, kVp

Factors to consider when calculating the required protective barrier thickness of an x-ray room: distance:

The thickness of barrier naturally depends on the distance between the source of radiation and the barrier

Factors to consider when calculating the required protective barrier thickness of an x-ray room: occupancy:

The use of the area that is being protected is of principal importance.

What is the T factors for full occupancy?

1

What is the T factor for frequent occupancy?

¼

What is the T factor for occasional occupancy?

1/16

What areas are considered full occupancy?

Work ahead (offices, labs, shops, wards, and nursing stations), living quarters, children’s play rooms, and occupied space in nearby buildings

What areas are considered frequency occupancy?

Corridors, patient rooms, and restrooms (CPR)

What areas are considered occasional occupancy?

Outside area, janitor’s closets, waiting rooms, unattended elevators, and stairways (OJWUS)

What is the workload?

Number of exams performed per week (mAmin/week). Thicker the shield, the more the exams

What is the use factor?

the % of time the x-ray beam is on and directed toward a particular protective barrier (wall)

kVp

Used as the measure of penetrability. Operate up to 150 kVp but average of 75 kVp

What is the percentage of x-ray attenuation with a 0.25 mm Pb lead apron at 50 kVp?

97%

What is the percentage of x-ray attenuation with a 0.25 mm Pb lead apron at 75 kVp?

66%

What is the percentage of x-ray attenuation with a 0.25 mm Pb lead apron at 100 kVp?

51%

What is the percentage of x-ray attenuation with a 0.5 mm Pb lead apron at 50 kVp?

99.9%

What is the percentage of x-ray attenuation with a 0.5 mm Pb lead apron at 75 kVp?

88%

What is the percentage of x-ray attenuation with a 0.5 mm Pb lead apron at 100 kVp?

75%

What is the percentage of x-ray attenuation with a 1.0 mm Pb lead apron at 50 kVp?

99.9%

What is the percentage of x-ray attenuation with a 1.0 mm Pb lead apron at 75 kVp?

99%

What is the percentage of x-ray attenuation with a 1.0 mm Pb lead apron at 100 kVp?

94%

What are the advantages of a film badge?

• Readily processed by labs

• Simple, inexpensive

• Provide permanent record by labs

What are the disadvantages of a film badge?

• Sensitive to extremes in temp, humidity, and light leaks

• Not reusable

• Accuracy +/ - 10-20%. Low limit of sensitivity (.1 mSv)

What are the advantages of TLD?

• Can be made very small

• Exposure rate .05 mSv

• Accuracy to +/ - 5%

• Response very similar to tissue

• Less sensitive to heat than film badge

What are the disadvantages of TLD?

• Cannot be stored as a permanent record

• More expensive than film badge

What are the advantages of OSL?

• Dose measurement range very wide (.01 mSv-10 mSv)

• Accuracy =/ - 15% for shallow deep exposures

• Precision within +/ - 0.1 mSv

• Reanalysis can be restimulated many times

• Bimonthly readout offered

• Not affected by heat, moisture or pressure

What are the disadvantages of OSL?

More expensive than film badges and TDL’s

Which of the field survey instruments is utilized in gamma cameras for nuclear medicine?

Scintillation detection device

What is the intensity of scatter radiation at 1 meter from the patient?

Approximately 0.1% of the intensity or 1/1000 of the useful beam. To calculate: multiply by 0.001 (divide by 1000)

Typical effective dose and ESE per exam: PA chest:

2 mGya

Typical effective dose and ESE per exam: average skull:

2 mGya

Typical effective dose and ESE per exam: lateral skull:

0.7 mGya

Typical effective dose and ESE per exam: AP cervical spine:

1-1.5 mGya

Typical effective dose and ESE per exam: AP T-spine:

1.8 mGya

Typical effective dose and ESE per exam: AP lumbar spine:

3 mGya

Typical effective dose and ESE per exam: AP abdomen:

4 mGya

Typical effective dose and ESE per exam: AP pelvis:

1.5 mGya

Typical effective dose and ESE per exam: average extremity:

0.5 mGya

What are the formulas used for calculate effective dose?

• E= E x Dt x Wt

• E = Wr x Wt x absorbed

What does Wr = for x-ray?

1

What is the Pb eq for the Bucky slot cover?

At least .25 mm Pb eq (does not protect patient)

What is the Pb eq for the protective curtain/drapes?

At least 0.25 mm Pb eq (placed between you and the patient

For mobile fluoroscopy, what is the minimum SSD?

Must not be less than 12” (30 cm)

For stationary fluoroscopy, what is the minimum SSD?

15” (38 cm)

What is the relationship between FOV, magnification, and patient dose?

As field of view decreases, magnification of the output screen image increase and patient dose increases

What is a Geiger-Müller counter?

Used to detect alpha and beta and radiation. Gas filled tube detector

Occupational radiation exposure of radiologic personnel: average whole-body dose:

0.7 mSv/year

Occupational radiation exposure of radiologic personnel: those receiving less than the minimum detectable dose “M'“:

53%

Occupational radiation exposure of radiologic personnel: those receiving less than 1 mSv/year:

88%

Occupational radiation exposure of radiologic personnel: those receiving greater than 50 mSv/year (over the annual dose recommendations):

0.05%

The intensity of the x-ray beam at the tabletop of a fluoroscopy should not exceed ______ per minute for each mA of operation at 80 kVp

21 mGy

NCRP report #102 mobile radiography recommendations:

• Exposure switch must allow operator to remain at least 2 m (6ft) from the pt, x-ray tube, and useful be am

• A lead apron must be assigned/carried for each mobile unit for the operator

• Alert individuals in the area before making an exposure

• Shield radiosensitive organs

• Primary beam must be directed away from the technologist and at a 90 degree angle

What are the materials found in TLDs?

Lithium fluoride or calcium fluoride crystals

What are the materials found in OSLs?

Aluminum oxide (Al2O3)

What is reproducibility?

Output exposure should be consistent from one exposure to another. Same technique for repeat exposures

What is reciprocity?

Amount of x-ray intensity should remain consistent at specific mAs value despite the different combinations of mA and time. Sam radiation output

What is the effects of 30 degree C-arm tilt for person standing next to C-arm?

Will increase the dose to the face and neck region of the patient and the image intensifier above the patient

What are the effect of tube on top?

Not recommended because it could increase the dose to the operators eyes up to 100x’s

What is PBL?

Positive beam limitation: automatic light-localized, variable-aperture collimators. Only required between 1974-1994

Entrance skin exposure (ESE)

Reported most often because it is easy to measure. Exit skin dose is 1% of entrance skin dose. HVL of x-rays in soft tissue= 4 cm

Bone marrow dose (mean marrow dose)

The average radiation dose to the entire active bone marrow. Largest organ responsible for stochastic response of radiation induced leukemia

Gonadal dose (genetically significant dose)

Measurement and estimates of gonad dose are important because of suspected genetic effect of radiation

Genetically significant dose (GSD) defined:

The gonad 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 dose actually recieved or a weighted average gonad dose

Effective dose

The dose to the whole body that would cause the same harm as a partial or localized dose for a particular x-ray exam or equivalent whole-body dose

Methods of patient dose reduction (grids vs collimation/beam restriction)

• Grids result in an increase in patient dose

• Beam restriction reduces patient dose, by limiting the size and shape of the x-ray beam to only area of interest

Major organogenesis: 0-2 weeks

• All or nothing, spontaneous abortion or carried to term; no ill effects

• Natural occurance: 25%

• Radiation response: 0.1%