Dosimetry

Question 1

In the MIRD schema, dose rate is proportional to

Answer 1

Question 2

The absorbed fraction is

Answer 2

energy absorbed in a target / energe emitted from a source

Question 3

Typical ranges of radiations

alphas

betas

conversion and auger electrons

x-rays

gamma rays

Answer 3

um

mm

mm

mm to cm

cm to m

Question 4

The S-factor is dependent on

Answer 4

organ shape, size and location of radioactivity

Question 5

typical s-factor units

Answer 5

Gy/Bq-s or rad/uCi-hr

Question 6

Absorbed dose is

Answer 6

E/M (Gy)

absorbed energ / mass

Question 7

How is Air Kerma different than Absorbed Dose

Answer 7

The unit for kerma is joule per kilogram (gray (Gy)), which is the same as for absorbed dose. However, Kerma dose is different from absorbed dose, according to the energies involved, partially because ionization energy is not accounted for. Whilst roughly equal at low energies, kerma is much higher than absorbed dose at higher energies, as some of the energy escapes from the absorbing volume in the form of bremsstrahlung X-rays or fast moving electrons.

Question 8

MIRD dosimetry is described in

Answer 8

MIRD Pamphlet 21 (2009)

Question 9

Quality Factor has been replaced by

Answer 9

“weighting factor” w_rwhich is dependent on the radiation of interest.

For example alpha particles have a w_r of 20

Question 10

The difference between w_r and RBE

Answer 10

RBE (relative biological effectiveness) deals with deterministic effects such as cell killing while w_r depends on the biolgocial endpoint. For example RBE for alphas is 1 to 8 for cell killing in vivo while w_r is 20 to reflect the relative risk of cancer. w_r is from the ICRP