Maximum Permissible Dose (MPD)

In This Lecture

Revision

Radiation Protection Criteria & Exposure Limit

ALARA Principle

Radiation Protection Philosophy

Principles and 10 Commandments of Radiation Protection

Radiation warning signs

Maximum Permissible Dose (MPD)

Risk Factor

Ionizing Radiation Effects

• Probability of effect occurring is governed by laws of chance• Therefore, greater the dose the greater the probability of effect

occurring.• No safe dose limit - ALL doses carries some risk• Severity of effect is not related to dose

• Examples: Cancers & Genetic effects.

STOCHASTIC EFFECTS

DETERMINISTIC EFFECTS

• Severity increases with dose.• Usually threshold below which no effect occurs.• Examples: Erythema, Epilation & Cataract.

Radiation Protection Criteria & Exposure Limit

The objective of radiation protection is to balance the risks and benefits from activities that involve radiation.

Exposure guidelines keep risks of harm from radiation within the levels that society allows.

Specific radiation protection standard recommended by:ICRP: International Commission on Radiological Protection.

NCRP: National Council on Radiation Protection and Measurements.

Different permissible exposure criteria are applied to different groups of persons:

Occupational or “on-site” standards for persons who work with radiation (18-60) years “Controlled exposure”.

Non-occupational or “off-site” guides for general public. Usually 10% of the allowable occupational values “In voluntary exposure”

How is ALARA used in the practice of radiation protection?

• ALARA is a basic radiation protection concept or philosophy. It is an application of the "Linear No Threshold Hypothesis," which assumes that there is no "safe" dose of radiation. Under this assumption, the probability for harmful biological effects increases with increased radiation dose, no matter how small. Therefore, it is important to keep radiation doses to affected populations (for example, radiation workers, minors, visitors, students, members of the general public, etc.) As Low As Reasonably Achievable (ALARA).

Where are ALARA principles utilized?

• ALARA principles can be utilized in an infinite number of situations. For example, the proper design of a nuclear facility depends on ALARA considerations (e.g., can the addition of more shielding to an area be justified in terms of the lower doses it will achieve?). In addition, designing an x-ray facility for medical applications requires consideration of the amount of shielding needed to ensure that individuals located near the facility (e.g., on the other side of the wall from the x-ray unit) do not receive any more dose than is really necessary during operation of the x-ray device.

ALARA Principles

Source reduction “elimination”.

Controlling and containing the radioactivity.

Minimizing time in radiation field.

Maximizing the distance from radiation source.

Using proper shielding.

Optimization rule in radiation protection.

Principles of Radiation Protection

(Philosophy) Justification: Radiation must not be used unless the benefit

associated with that use outweighs the associated risks.

Optimization: As Low As Reasonably Achievable (ALARA)

The magnitude of individual doses, the number of people exposed, and the likelihood of incurring exposures from a justified application of radiation must be kept ALARA or As Low As Reasonably Achievable.

Dose Limits: no individual exposure is to exceed a predetermined regulatory limit, appropriate to the circumstances.

Do not define a fine line between safe and dangerous levels of exposure.

Principles and 10 Commandments of Radiation Protection

No Principle Commandment (familiar)

1. Time Hurry (but don't be hasty)

2. Distance Stay away from it or upwind of it

3. Dispersal Disperse it and dilute it

4. Source Reduction Make and use as little as possible

5. Source Barrier Keep it in

6. Personal Barrier Keep it out

7. Decorporation (Internal & skin) Get it out of you and off of you

8. Effect Mitigation Limit the damage

9. Optimal Technology Choose best technology

10. Limitation of Other Exposures Don’t compound risks (don’t smoke)

RADIATION WARNING SIGNS• As radiation is considered a

hazard, it is important to make people aware of its presence since it can’t be seen, heard, smelled, or sensed by humans

• International symbol indicating radioactive hazard in the black three foil on a yellow background

RADIATION WARNING SIGNS

• Supplementary warning sing recently introduced by the IAEA (International Atomic Energy Agency)

• Black on red background.

Maximum Permissible Dose • Government standards for radiation protection are established

by the National Council on Radiation Protection and Measurement (NCRP) and its international counterpart, the International Commission on Radiological Protection (ICRP). Both of these organizations offer recommendations for the maximum permissible dose (MPD) of radiation to which people should be exposed, and those recommendations are generally adopted by various government regulatory agencies like (JAEC) as the maximum limits permitted by law.

• Maximum permissible dose (MPD) is affected both by the size of each dose and the rate at which these doses are received.

Maximum Permissible Dose

Date Dose for General Public(mSv)

Dose for Radiation Worker(mSv)

1931 50 5001936 30 3001948 15 1501958 5 501990 1 20

History of Maximum permissible Dose

Criteria NCRP-116 ICRP-60Occupational Exposure Effective Dose Annual 50 mSv 20 mSv

Effective Dose Cumulative 10 mSv × age (y) 100 mSv in 5 years

Equivalent Dose Annual

150 mSv lens of eye; 500 mSv skin, hands, feet

150 mSv lens of eye; 500 mSv skin, hands, feet

Pregnant 5 mSv 2 mSvPublic Exposure

Effective Dose Annual

1 mSv if continuous5 mSv if infrequent

1 mSv; higher if needed, provided 5-y annual average ≤ 1 mSv

Equivalent Dose Annual

15 mSv lens of eye;50 mSv skin, hands, feet

15 mSv lens of eye;50 mSv skin, hands, feet

Exposure Limits from NCRP Report No. 116 and ICRP Publication 60

Example:A radiation worker is 31 years of age. What is his cumulative effective-dose limit in mSv according to:(a) the NCRP?(b) the ICRP?

Maximum Permissible Dose

Answer:

(a) NCRP :

31 × 10mSv = 310 mSv

(b) ICRP :

(31-18) × 20mSv = 260 mSv

Risk Factor

population by received equivalent Dosepopulationof Size

casesof Number

(r) Risk

Units: Sv-1

Risk FactorTissue (T) Risk Coefficient *WT

Gonads 40 × 10-4 Sv-1 ( 40 × 10-4 rem-1 ) 0.25Breast 25 × 10-4 Sv-1 ( 25 × 10-4 rem-1 ) 0.15Red bone marrow 20 × 10-4 Sv-1 ( 20 × 10-4 rem-1 ) 0.12Lung 20 × 10-4 Sv-1 ( 20 × 10-4 rem-1 ) 0.12Thyroid 5 × 10-4 Sv-1 ( 5 × 10-4 rem-1 ) 0.03Bone surface 5 × 10-4 Sv-1 ( 5 × 10-4 rem-1 ) 0.03Remainder 50 × 10-4 Sv-1 ( 50 × 10-4 rem-1 ) 0.30Total 165 × 10-4 Sv-1 ( 165 × 10-4 rem-1 ) 1.00

Calculated from data in 1CRP # 26* These "weighting factors" are simply the fractions of the overall risk, i.e. entries in column # 2 divided by 165 x 10-4 “Total Risk”.

Example:The Risk factor for radiation-induced leukemia is estimated to be 20×10-4 Sv-1 , if each member of a population of 1 million receives a 1 Sv dose how many leukemia's will occur?

Answer: 20×10-4 × (1×106) = 2000 cases

Risk Factor

1 Sv ≈ 50,000 chest X-rays

Annual Recommended Dose Limits & Reference values for diagnostic x-ray examinations

Applicable Body Organ or Tissue Radiation Workers PublicWhole body 20 mSv 1 mSv

Lens of the eye 150 mSv 15 mSvSkin 500 mSv 50 mSv

Hands 500 mSv 50 mSvAll other organs 500 mSv 50 mSv