Radiation Numbers

Question 1

What dose equivalent rate defines a radiation area?

Answer 1

Radiation area means an area, accessible to individuals, in which radiation levels could result in an individual receiving a dose equivalent in excess of 5 mrem (0.05 mSv) in 1 hour at 30 centimeters from the radiation source or from any surface that the radiation penetrates.

Question 2

What is the maximal dose rate limit for unrestricted areas?

Answer 2

The Nuclear Regulatory Commission (NRC) defines that the dose in any unrestricted area from external sources, exclusive of the dose contributions from patients administered radioactive material and released, does not exceed 2 mrem (0.02 millisievert) in any 1 hour. Unrestricted areas would include waiting rooms, hallways, file space, and secretarial areas.

Question 3

An individual who has been administered unsealed by-product material may be released if the total effective dose equivalent to any other individual from exposure is not likely to exceed which of the following?

Answer 3

A licensee may authorize the release from its control of any individual who has been administered unsealed by-product material or implants containing by-product material if the total effective dose equivalent to any other individual from exposure to the released individual is not likely to exceed 0.5 rem (5 mSv).

Question 4

What are considered major spills?

Answer 4

• Tc-99m and TI-201 = 100 mCi
• In-111, Ga-67, I-123 = 10 mCi
• I-131 = 1 mCi

Question 5

What is the SI unit for absorbed dose?

Answer 5

The Gy

The SI unit of dose is the Gy. Dose is defined as the energy deposited per unit mass. The unit Gy is defined as 1 J/kg.

Question 6

What is the threshold for permanent sterility in males from an acute exposure, approximately?

Answer 6

6 Gy

Question 7

Which equipment should be used to test for Mo-99 breakthrough?

What ratio of Mo-99 to Tc-99m is required to pass the Mo-99 breakthrough test?

Answer 7

When eluting a Tc-99m generator, the mother isotope Mo-99 can contaminate the eluate. It is required to test for Mo-99 breakthrough in each eluate. This is done by placing the eluate in a special lead pig and placing it in the dose calibrator for a reading. The lead pig is then removed and the eluate is placed in a plastic sleeve for a reading in the dose calibrator. A ratio of Mo-99 to Tc-99m of less than 0.15 uCi Mo-99/mCi Tc-99m is required to pass the Mo-99 breakthrough test.

Question 8

Regarding pregnant patients, how does CTPA radiation exposure to the mother compare to VQ scans?

Answer 8

Fetal dose in CTPA ranges between 0.013 and 0.026 mGy in early and 0.06-0.1 mGy in late pregnancy compared with perfusion scintigraphy with a fetal dose of 0.1-0.6 mGy in early and 0.6-0.8 mGy in late pregnancy. Aerosol ventilation scintigraphy results in 0.1-0.3 mGy. However, the breast radiation from CTPA is much higher to the mother than VQ scans. Use of shielding and automated exposure controls can help reduce CT radiation dose.

Question 9

The unit of equivalent dose is given the special name of Sievert (Sv). What are the units of equivalent dose?

Answer 9

Equivalent dose has units of J/kg. In radiation protection, the quantity is given the special name of Sievert (Sv).

1 Sv = 1 J/kg, 1 Sv = 100 rem

Question 10

In the SI system, exposure is indicated using which of the following units?

What is the historical unit of exposure?

Answer 10

Exposure is the quantity of charge in air due to ionization from x- or gamma rays. The unit of charge is the Coulomb, C. In the SI system, exposure is simply represented by the units C/kg. The historical unit of exposure is the roentgen (R).

Question 11

What is the threshold for cataracts caused from an acute exposure to the eye (onset > 20 years)?

Answer 11

The threshold for cataracts from an acute exposure is ~ 0.5 Gy (50 rads).

Cataracts will develop over 20 years after acute exposure.

Question 12

What is the limit to a general member of the public from activities performed involving the use of radiation?

What is the maximum dose an individual member of the public may receive from the release of patients injected with radioactive materials (e.g., thyroid ablation patients)?

Answer 12

The dose limit to a general member of the public from activities performed involving the use of radiation is 1 mSv (100 mrem).

5 mSv (500 mrem) is the maximum dose an individual member of the public may receive from the release of patients injected with radioactive materials.

Question 13

What is the maximal permissible radioactivity ratio of Mo-99 to Tc-99m allowed in an elution from a Mo-99/Tc-99m generator?

Answer 13

The maximal permissible radioactivity ratio of Mo-99 to Tc-99m allowed in an elution from a Mo-99/Tc-99m generator is 0.15 uCi/mCi. This type of impurity is referred to as radionuclidic.

Question 14

What is the unit of radioactivity?

Answer 14

The unit of radioactivity is the becquerel (Bq) or the curie (Ci), where 1 Ci = 3.7 x 10^10 Bq and 1 Bq = 1 disintegration per second. Activity is a measure of the number of transformations (decays) that a mass of radioactive atoms will undergo per unit time.

Question 15

According to 10 CFR 20, the maximum dose a worker may receive to his or her whole body in a year is which of the following?

What is the dose limit for a pregnant worker?

How many rem in 1 Sv?

Answer 15

5 rem is the annual occupational dose limit to the whole body.

The dose limit for a pregnant worker is 500 mrem.

1 Sv = 100 rem, therefore 5 Sv = 500 rem, and 0.5 Sv = 50 rem.

Question 16

What is the reported threshold dose for temporary sterility in males from an ACUTE exposure?

Answer 16

ICRP 118 gives the threshold for temporary sterility in males from an ACUTE exposure as ~ 0.1 Gy (Table 4.4, page 298). Note that ICRP 118 lists the threshold values at the 1% incidence level. ICRP 118 further reports recovery of spermatogenesis is expected after 9-18 months following a single dose of 1 Gy, after 30 months for doses 2-3 Gy, and after 5 years for a dose of about 4 Gy (ICRP 118, page 83).

Question 17

According to the NRC, what is the annual dose limit to the public?

Answer 17

1 mSv

Question 18

Regarding the release of individuals treated with unsealed by-product material (i.e., I-131 NaI), written instructions to that individual are required by the Nuclear Regulatory Commission (NRC) to reduce exposure to others if the exposure to any other individual exceeds what dose?

Answer 18

A licensee shall provide the released individual, or the individual’s parent or guardian, with instructions, including written instructions, on actions recommended to maintain doses to other individuals as low as is reasonably achievable if the total effective dose equivalent to any other individual is likely to exceed 1 mSv (0.1 rem).

Question 19

What is the measure of the amount of radiation absorbed by human tissue?

Answer 19

Radiation absorbed dose (RAD) is a measure of the absorbed dose (energy deposited) in a material, whether human tissue, lead, water, etc. One RAD is the deposition of 100 ergs of energy in 1 gram of any material due to the ionization from any type of radiation.

Roentegen unit, Roentgen equivalent man (REM), and Sievert (Sv) are all units that have been used or are currently used to describe the probability of biological effects of ionizing radiation (e.g., cancer).

Question 20

What is the annual whole body dose limit for occupational workers?

Answer 20

The Nuclear Regulatory Commission (NRC) states that the licensee shall control the occupational dose to individual adults to an annual total effective dose equivalent to 5 rem (0.05 Sv).

Question 21

What is the Chest CT screening dose limit?

Answer 21

below CTDIvol 3mGy

Question 22

Sievert is the unit of ________. Exposure is measured in _/_, and the SI unit for activity is____.

Answer 22

Sievert is the unit of equivalent dose. Exposure is measured in C/kg, and the SI unit for activity is bequerel (Bq).

Question 23

Acute threshold dose for sterility in males? How about females?

Answer 23

The threshold dose for permanent sterility in males is ~ 6 Gy, acute. Different developmental stages of sperm have varying radiosensitivity; some stages of transient sterility can occur at < 1 Gy. However, fertility recovers up to ~ 6 Gy.

The threshold dose for permanent sterility in females is ~ 3 Gy. The LD_50 for the human oocyte, which is understood to be the cause of radiation-induced infertility, is estimated to be less than 2 Gy. Radiation-induced infertility occurs more often in older women due to reduced number of oocytes with increasing age.

Question 24

The unit of kinetic energy released in a mass (kerma) is a measure of what? What is the units?

Answer 24

Kinetic energy released in a mass (kerma) is a measure of the total initial kinetic energy of all charged particles liberated by uncharged particles per unit mass. It has units of J/kg, or Gy.

Question 25

Under the Mammography Quality Standards Act Regulations (MQSA), the measured glandular dose from a single craniocaudal view acquired using using techniques for a standard breast shall not exceed?

Answer 25

3mGy

Question 26

What is the threshold for transient erythema for human skin, approximately?

Answer 26

The threshold for transient erythema for human skin is approximately 2 Gy (200 rads).

Question 27

The threshold dose for the main erythema reaction in human skin is approximately what dose?

Answer 27

The terms as defined by the International Commission on Radiological Protection (ICRP) include an early transient erythema seen a few hours after doses of 2 Gy. The main erythema reaction is at ~ 10 days and is secondary to inflammation and cell death of the basal epidermal layer and occurs at ~ 5 Gy. A late erythema can be seen 8-10 weeks after exposure and is bluish secondary to ischemic changes (~ 15 Gy).