EXAM #1 (Ch. 35 Health Physics)

Question 1

Define: health physics

Answer 1

The scientific discipline of radiation protection.

Question 2

Define: TVL

Answer 2

Tenth value layer. That thickness of material that will reduce radiation intensity to one tenth its unattenuated value.

Question 3

Define: NCRP

Answer 3

NCRP is an acronym for National Council on Radiation Protection and Measurement.

Question 4

Define: effective dose

Answer 4

Concept that attempts to specify the overall risk of harm to an organism by accounting for two variables with the use of appropriate weighting factors.

Question 5

Define: ALARA

Answer 5

As low as reasonably achievable.

Question 6

Define: tissue weighting factor (Wt)

Answer 6

A numerical index of the relative radiosensitivity of various tissues.

Question 7

Define: first responder

Answer 7

Early people on the scene of a radiologic terrorism event who must make the first decisions.

Question 8

Define: Clarence Dally

Answer 8

Considered to be the first x-ray fatality. An assistant to Thomas Edison.

Question 9

Define: Manhattan Project

Answer 9

The name of the World War II project to develop the atomic bomb.

Question 10

Define: LNT

Answer 10

LNT is an acronym for linear nonthreshold dose-response relationship.

Question 11

Write the equation for the radiation dose as a function of time of exposure.

Answer 11

Dose = dose rate × time.

Question 12

What is the function of the 5-minute reset timer on a fluoroscopy imaging system?

Answer 12

To help ensure that the radiologist is aware of the fluoroscopic exposure time and prevent exceeding the five-minute of exposure.

Question 13

A fluoroscope emits 35 µGya/mA-minute at the tabletop for every mA of operation. What is the approximate patient entrance skin dose (ESD) after a 3.2-minute fluoroscopic examination of 1.5 mA?

Answer 13

(35 µGya/mA/min)(3.2 min)(1.5 mA) = 168 µGya

Question 14

What are the three cardinal principles of radiation protection?

Answer 14

Minimize time, maximize distance, use shielding material.

Question 15

The output intensity of a radiographic unit is 42 µGya/mAs. What is the total output after a 200-ms exposure at 300 mA?

Answer 15

(42 uGya/mAs) × (300 mA × 0.2 s) = 2.52 mGya.

Question 16

At the exposure rate 42 µGya/mAs, what is the approximate patient skin dose after a 3.2-minute fluoroscopic examination of 1.5 mA?

Answer 16

(42 uGya/mAs) × (3.2 min × 60 s/min) × 1.5 mA = 12096 uGya. = 12 mGya.

Question 17

How can the three cardinal principles of radiation protection be best applied in diagnostic radiology?

Answer 17

The three cardinal principles of radiation protection to be applied in diagnostic radiology are as follows: minimize the time of radiation exposure, maximize the distance from the source, wear protective apparel.

Question 18

What exposure will a radiologic technologist receive when exposed for 10 minutes at 4 m from a source with intensity of 1 mGya/hr at 1 m while wearing a protective apron equivalent to 2 HVLs?

Answer 18

(1 mGya/hour) × (1 hour/6) × (1 m/4 m)2 × (1/4) = 2.6 uGya.

Question 19

What wartime effort coined the term health physicist?

Answer 19

The Manhattan Project.

Question 20

The collar-positioned monitor of a fluoroscopist records 0.9 mSv over the course of a month. This represents approximately what effective dose (E)?

Answer 20

Effective dose applies only to thyroid = 0.9 mSv × 0.05 = 0.045 mSv = 45 uSv.

Question 21

Describe the change in longevity that occurred during the 20th century and the impact of radiation on that change.

Answer 21

Life expectancy nearly doubled, and much of that increased longevity is due to medical imaging.

Question 22

How many half-value layers are included in a tenth-value layer?

Answer 22

1 TVL = 3.3 HVL.

Question 23

What should first responders do in the event of a radiologic emergency?

Answer 23

First attend to the medical needs of the injured. Then attempt to determine if radioactive contamination has occurred.

Question 24

Discuss the concept of effective dose.

Answer 24

The whole body dose that carries the same risk as a partial body exposure.