1. Internal Radiation Dosimetry Lab 9

2. Radiation Measurement • We use different terms depending on whether: • The radiation is coming from a radioactive source • The radiation dose absorbed by a person • The risk that a person will suffer health effects from exposure to radiation

3. 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.

4. Radiation Dosimetry The damaging effects arise from the absorption of energy in tissues and depend on a number of factors: • The activity of the administered radiopharmaceutical • The physical and biological half-lives of the radiopharmaceutical • The distribution and metabolic fate of the radiopharmaceutical in the body • The fraction of energy released per disintegration from a source region that is absorbed in the particular target volume • The shape, composition, and location of the source and target organs

5. Radiation Units • There are three basic units related to radiation: • The roentgen (R) for exposure • The rad (radiation absorbed dose) for absorbed dose • The rem (roentgen equivalent man) for dose equivalent.

6. Units and Terminology • Two systems of measurement • Conventional • roentgen • rad • rem • SI (Systeme Internationale) • exposure • gray • sievert

7. Conversion between various units used in radiation

8. 1st Definition: Exposure • Definition: Charge per unit mass of air • One of the earliest radiation measurements • Unit: Rontegen (R)

9. 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

10. 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

11. 3rd Definition: Relative Biological Effectiveness • Peak kilovoltage (kVp) is the maximum voltage applied across an X-ray tube.

12. Biological Effects, continued • Conventional system: • Rem (“Roentgen equivalent man”) • Systeme Internationale: • Sievert (Sv)

13. 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)

14. 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.

15. Thank You