Internal Radiation Dosimetry

Lab 9

Radiation Measurement

• We use different terms depending on whether:

1. The radiation is coming from a radioactive source

2. The radiation dose absorbed by a person

3. The risk that a person will suffer health effects from exposure to radiation

Radiation Dosimetry

• Radiation can cause deleterious effects in living systems. It is therefore essential to assess these effects in humans for a given nuclear medicine procedure involving the administration of a radiopharmaceutical.

Radiation Dosimetry

1. The activity of the administered radiopharmaceutical

2. The physical and biological half-lives of the radiopharmaceutical

3. The distribution and metabolic fate of the radiopharmaceutical in the body

4. The fraction of energy released per disintegration from a source region that is absorbed in the particular target volume

5. The shape, composition, and location of the source and target organs

The damaging effects arise from the absorption of energy in tissues and depend on a number of factors:

Radiation Units

• There are three basic units related to radiation:

1. The roentgen (R) for exposure

2. The rad (radiation absorbed dose) for absorbed dose

3. The rem (roentgen equivalent man) for dose equivalent.

Units and Terminology

• Two systems of measurement

1.Conventional– roentgen– rad– rem

2.SI (Systeme Internationale)– exposure– gray– sievert

Conversion between various units used in radiation

1st Definition: Exposure

• Definition: Charge per unit mass of air • One of the earliest radiation measurements• Unit: Rontegen (R)

2nd Definition: Absorbed Dose

• Definition: It is a measure of the energy deposited in unit mass of any material by any type of radiation (i.e., energy per gram)

• Conventional units– rad – 100 ergs of energy per 1 gm of material

• Systeme Internationale– Gray (abbreviated Gy) – 1 joule/kg– 1 Gy = 100 rad

3rd Definition: Relative Biological Effectiveness

• Relative biological effectiveness (RBE) is a measure of these differences in living tissue

• The higher the number, the more damaging the radiation is, for the same amount of absorbed energy.

• Radiation damage depends on– Type of material– Type of radiation

3rd Definition: Relative Biological Effectiveness

• Peak kilovoltage (kVp) is the maximum voltage applied across an X-ray tube.

Biological Effects, continued

• Conventional system:– Rem (“Roentgen equivalent man”)

• Systeme Internationale:– Sievert (Sv)

4th Dose Equivalent Unit • The dose equivalent unit (Hr) has been developed to

account for the differences in effectiveness of different radiations in causing biological damage.

• Defined as the ratio of the dose of a standard radiation to produce a particular biological response to the dose of the radiation in question to produce the same biological response.

• Unit: – Rontegen Equivalent Man (rem)– Sievert (Sv)

4th Definition Dose Equivalent Unit • For a particular radiation is defined as

• Where rad = absorbed dose in rad• (RBE)r is the relative biological effectiveness of the

radiation.

Thank You