ProtectionTaoran Cui and Peng Qi

RADIATION PROTECTION

TAORAN CUI AND PENG QI

Question 1

In the United States, which agency provides guidelines for radiation protection?

Question 2

According to the National Council for Radiation Protection and Measurements (NCRP), what are the two main objectives of radiation protection?

Question 3

What is the major difference between the deterministic effects and stochastic effects?

Question 4

Which quantities are used in the latest National Council for Radiation Protection and Measurements (NCRP) reports on radiation protection?

Question 1 In the United States, which agency provides guidelines for radiation protection?

Answer 1

The National Council for Radiation Protection and Measurements (NCRP) provides recommendations for radiation protection. The NCRP recommendations are directly related to the Biological Effects of Ionizing Radiation (BEIR) reports, of which the latest is BEIR VII report of 2006.

National Council on Radiation Protection and Measurements. Risk Estimates for Radiation Protection. NCRP Report No. 115; Bethesda: MD; 1993.

Question 2 According to the National Council for Radiation Protection and Measurements (NCRP), what are the two main objectives of radiation protection?

Answer 2

1. To prevent clinically significant radiation-induced deterministic effects by adhering to dose limits that are below the apparent or practical threshold.

2. To reduce the probability of stochastic effects as a result of occupational exposure to ionizing radiation.

National Council on Radiation Protection and Measurements. Risk Estimates for Radiation Protection. NCRP Report No. 115, Bethesda, MD; 1993.

Question 3 What is the major difference between the deterministic effects and stochastic effects?

Answer 3

Deterministic effect has a threshold of dose and the severity is dose dependent, whereas stochastic effect does not have a dose threshold and is not dose dependent. Examples of deterministic effects are skin erythema, hair loss, and cataracts. Stochastic effects include radiation carcinogenesis and hereditary effects.

Cember H, Johnson TE. Radiation safety guides. In: Cember H, Johnson TE, eds. Introduction to Health Physics. 4th ed. New York, NY: McGraw-Hill; 2009:344–347.

Question 4 Which quantities are used in the latest National Council for Radiation Protection and Measurements (NCRP) reports on radiation protection?

Answer 4

Equivalent dose and effective dose have been recommended by the internal organization: International Commission of Radiological Protection (ICRP). Other quantities have been used or are still used including exposure (unit: R), radiation absorbed dose (unit: rad or Gy), occupational exposure (unit: rem), and dose equivalent.

National Council on Radiation Protection and Measurements. SI Units in Radiation Protection and Measurements. NCRP Report No. 82, Bethesda, MD; 1985.

Question 5

What is equivalent dose?

Question 6

What are the latest recommended values for radiation weighting factor w_R by the International Commission on Radiological Protection (ICRP)?

Question 7

What is effective dose?

Question 5 What is equivalent dose?

Answer 5

Equivalent dose (H_T) is defined as the radiation-weighted sum of the absorbed dose in a tissue or organ (D_T,R), given by the expression:

where w_R is the radiation weighting factor. The unit of equivalent dose is given the special name Sievert (Sv), and 1 Sv is equal to 1 J/kg.

Hall EJ, Giaccia AJ. Radiation protection. In: Hall EJ, Giaccia AJ, eds. Radiobiology for the Radiologist. 7th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2006:224–239.

Question 6 What are the latest recommended values for radiation weighting factor w_R by the International Commission on Radiological Protection (ICRP)?

Answer 6

Type and Energy Range	Radiation Weighting Factor W_R
Photons	1
Electrons	1
Protons	2
α-particles, fission fragments, heavy nuclei	20
Neutrons	A continuous function of neutron on energy

Valentin J. The 2007 recommendations of the International Commission on Radiological Protection: Publication 103. Ann. ICRP 2010;37(2–4):1–332

Question 7 What is effective dose?

Answer 7

Effective dose (E) is the sum of all the weighted (w_T) equivalent doses in all the organs or tissues irradiated, given by:

The calculation of this quantity takes into account the sensitivity to radiation of different organs or tissues. The standard international (SI) unit of effective dose is the same as equivalent dose (unit: Sv). Both equivalent dose and effective dose are used to indicate the stochastic effects of ionizing radiation on the human body.

Hall EJ, Giaccia AJ. Radiation protection. In: Hall EJ, Giaccia AJ, eds. Radiobiology for the Radiologist. 7th ed. Philadelphia, PA: Lippincott Williams & Wilkins. 2006:224–239.

Question 8

What are the latest tissue weighting factors (w_T) recommended by the International Commission of Radiological Protection (ICRP)?

Question 9

Which quantity, equivalent dose or effective dose, should be used as the primary radiological protection quantity?

Question 10

What are the assumptions, simplifications, and approximations included in the definition of effective dose?

Question 8 What are the latest tissue weighting factors (w_T) recommended by the International Commission of Radiological Protection (ICRP)?

Answer 8

Tissue	w_T	∑w_T
Bone-marrow (red), colon, lung, stomach, breast	0.12	0.72
Gonads	0.08	0.08
Bladder, esophagus, liver, thyroid	0.04	0.16
Bone surface, brain, salivary glands, skin	0.01	0.04
		1