internal dosimetry

radiation dose (D)

amount of radiation energy deposited (absorbed) per gram of absorber material

equivalent dose (H)

dose delivered, taking into account the relative biological effect that the radiation has on the tissue

target organ

organ for which the dose is being measured

source organ

organ containing the source of radioactivity

source organ

must contain a concentration of activity > average concentration in body tissue

source organ activity

- amount in the organ

- duration that the activity will be there

amount of radiation energy emitted by the source organ

- energy of the emissions

- rate of decay (# of disintegrations)

fraction of emitted dose that the target will absorb

- type of emission

- energy of emission

- anatomic relationship

physical half life

elimination of the radioactivity by its normal physical decay

biological half life

elimination of the radioactivity by metabolic processes

effective half life

net half life resulting from the combination of physical half life & biological half life

effective half life

always ≤ the physical or biological half lives

cumulated activity

measure or total number of disintegrations occurring while the radioactivity is present in the source organ

equilibrium absorbed dose constant

energy emitted per unit of accumulated activity in the source

A∆

energy emitted by all the disintegrations during the time that the activity is in the source organ

absorbed fraction

fraction of energy emitted by the source which is absorbed by the target

average absorbed dose

energy absorbed by the target divided by the target's mass

average absorbed dose

summed for the total cumulative dose to the target organ

Absorbed Fraction

value depends on:

- type of emission from the source (particulate vs. gamma)

- E of emission from the source organ

- anatomic relationship of source & target organs

- volume & composition of target

medical internal radiation dosimetry committee

MIRD

mean dose per cumulative activity (S)

sum of the dose attributable to penetrating radiation from multiple emissions

mean dose per cumulative activity (S)

used to find the absorbed dose to an organ (target) from an organ (source)

mean dose per cumulative activity (S)

- unique for each radionuclide & target-source pair

- available from MIRD

- absorbed fraction is based on standard models of anatomy

- uniform distribution of activity in an organ

- uniform deposition of energy in an organ

- cumulated activity is prone to differences in pathophysiology

- cumulated activity for new pharmaceuticals is based on animal research

MIRD limits: assumptions

TBD

total energy deposited / mass of body