Doses and Biological Effects

Below are the steps in calculating the MIRD:

• Consider source organs and target organs –source organs are organs which radioactivity passes or resides through.
• Calculate the cumulative activity in each source organ.
• Look up physical data i.e. mass of target organ, radiation related data.
• Calculate the absorbed dose for each source/target situation:

  D = A/m  (DSifi), where:
  A is the accumulated activity
  m is the mass of the target organ
  Di is the equilibrium dose constant
  fi is the absorbed fraction

 

Click the MIRD Calculation 2 tab above to continue.

Account must be taken of all the different energies and abundances of radiations emitted.

One must not forget that many radionuclides emit tens of different radiations, not just those used in imaging.

DI (equilibrium dose constant) takes account of this.

 

Click the MIRD Calculation 3 tab above to continue.

• Next add up all contributions to a specific target organ to get total dose to that target organ.
• Then do the same for all irradiated organs
• Combine these together using the formulae for effective dose:
  E = S {(dose to target organ) x ( tissue weighting factor for this organ)}
  summed over all target organs.

 

Click the MIRD Calculation 4 tab above to continue.

A simplification to this process is possible in some cases:

MIRD have a value called ‘S’ - this is the absorbed dose per unit accumulated activity - these are listed in MIRD pamphlet 11.

If there is data that relates to your needs then the calculation becomes:

D = A x S

and hence E as before.