Physics

Question 1

“Joint Commission (JC) Sentinel Event is declared for unintended cumulative dose of

Answer 1

15 Gy to a single field (>1500 rads)

Question 2

“Leakage radiation from the x-ray tube housing is limited to”

Answer 2

1 mGy/h at a distance of 1 meter

Question 3

Max entrance air kerma (AK) rate in fluoro (non diagnostic) allowed by FDA is

Answer 3

100 mGy/min

No limit for DSA

Question 4

Fetal dose of > \_\_\_\_ 
are assoc. with
2w: fetal death
3-8w: congenital malformation
9-15w: growth or mental retardation

Answer 4

100 mGy

Question 5

A ____ fetal absorbed dose during the first trimester can result in x3.5 inc risk of childhood CA

Answer 5

10 mGy

Question 6

Dose rate limit of an unrestricted area

Answer 6

0.02 mSv in an hour

Question 7

Annual radiation dose limit (total body of adult occupational worker in the US):

Answer 7

50 mSv

Question 8

Avg risk of mortality from radiaton induced cancer in the gen pop

Answer 8

5% per Sv

Question 9

Avg Abd/Pelvic CT exam dose

Answer 9

9 mSv

Question 10

Natural background radiation in the United States

Answer 10

3 mSv/year

natural exposure: radon, solar etc.

Question 11

Standard voltage for a CXR

Answer 11

120 kVp

Question 12

Approximate power used to obtain an image with a plain film radiography

Answer 12

100 kW

Question 13

Approximate power used to obtain a mammogram

Answer 13

3 kW or 30 kW? fix this

Question 14

Appropriate entrance air kerma for an abdominal radiographs?

entrance skin dose?

Answer 14

3 mGy

~ 5mGy (usually about 50% more)

Question 15

Pediatric protocol change for CT

Answer 15

Decrease kVP (eg from 120 - 80), decrease mA, decrease SFOV. Sometimes slight increase in mA to decrease shot noise.

Question 16

Protocol change for CT in obese patients

Answer 16

Increase kVp to 140, and 120 for CTA

Question 17

Protocol change for CT in angiography or CECT

Answer 17

Set kVp = 100 (Increases vessel and tissue contrast by choosing kVp so that kVavg is just above the Kedge of iodine (33keV) but even higher than DSAs 70 kVp to avoid grainy images.

Question 18

Standard phantom sizes for CT
head ___
abdomen____

Answer 18

16 cm

32 cm

Question 19

Effective dose equation

Answer 19

K x DLP

Where K accounts for tissue being scanned (brain vs breast)

Question 20

Absorbed dose (mGy): Definition?

Answer 20

Energy absorbed per mass in J/kg.

CTDIvol

Question 21

Equivalent dose (mSv):

Answer 21

Multiply the absorbed dose by the RADIATION weighing factor (Wr).
Allows to compare radiation types by cancer risk

Question 22

Radiation weighing factor for XRays

Answer 22

1

so, equivalent = absorbed

Question 23

Radiation weighing for alpha rays

Answer 23

20

Question 24

Radiation weighing for gamma rays

Answer 24

1 (Same as XR)

Question 25

Effective dose

Answer 25

Multiply absorbed dose by TISSUE weighing factor. Accounts for tissue type irradiated (more radiosensitive tissues have larger Wt)

Question 26

1 Rem = ____ mSV

Answer 26

10

Question 27

Gamma should be shielded using

Answer 27

High Z material such as lead. Concrete can be used as building material.

Question 28

Termination should only be considered for fetal absorbed dose of ____ between the ____ weeks of gestation

Answer 28

> 50 mGy, 2-15

Question 29

Avg person in the US is exposed to approximately ____ mSv annually

Answer 29

6.2 | ~half from natural, half from medical

Question 30

Rad units operated above > 70kVp should contain a filtration of at least how much of aluminum equivalent

Answer 30

2.5mm

Question 31

Fetal absorbed doses of more than ____ occurring during ____ of gestation may result in fetal death.

Answer 31

25mGy, 3-8w

Question 32

The lethal dose in 50% of humans in 60 days is referred to as LD50/60 and occurs at what level of radiation?

Answer 32

3.5-7 Gy. Depends on level of medical care following exposure.

Question 33

What radiation induced cancer has the shortest latency period?

Answer 33

Leukemia (5-15yrs) | vs solid tumors 20-60yrs

Question 34

No deterministic effects from radiation have been proven below which does level?

Answer 34

0.1 Gy

Question 35

Improve streak artifact by

Answer 35

increasing kVp

Question 36

DLP equation

Answer 36

CTDIvol x scan length

Question 37

CTDIvol is estimated using

Answer 37

an acrylic phantom. | Overestimated in obese pts and underestimates in peds.

Question 38

Of the four basic dose units ________ is the closest measure of cancer risk; it accounts for both radiation type and tissue type.

Answer 38

effective dose

Question 39

Kerma-Area Product (KAP) equation

Answer 39

“KAP = AK x (Area Exposed)” measured in Gy-cm2

Question 40

KAP relates to _____ risk while AK relates to ______ risk.

Answer 40

stochastic (cancer); deterministic