Radiation Units

Radiation Units And Its Application

English Unit	SI Unit
Roentgen (R) = 2.58 * 10^-4 C/kg (coulomb per kilogram)	Coulomb/kg^-1 (C/kg)
RAD = 100 erg/gm	Gray (Gy) = 100 RAD
RBE=Dose in rad to produce same effect with x or gamma ray/ Dose in rad to produce same effect with radiation under investigation	No related term
REM = RBE x RAD REM = QF x RAD	Sievert (Sv) = 100 Rem Sv = QF x Gy
Quality Factor (QF) = LET	Same
curie (Ci) = 2.2 * 10¹² dpm Ci =3.7*10¹⁰ dps	becquerel (Bq) = 1 dps

Conversion Factor for Ci and Bq

1 Ci = 3.7 x 10¹⁰ Bq
1 Bq = 2.7 x 10^-11 Ci

Conversion factor for R and c/kg

1 R = 2.58 x 10^-4 C/kg
1 C/kg = 3.876 x 10³ R

Conversion factor for RAD and Gray

RAD = 100 erg/gm
Gy = 100 RAD

Conversion factor for REM and Sv

REM = RBE x RAD
Sv = 100 REM

Let's take a closer look at Prefixes to make sure you understand how to apply them with the different types of formulas we us in nuclear medicine.

R (Roentgen)

RAD (Radiation Absorbed Dose)

RBE (Relative Biological Effect)

Is a ratio comparing the biological effect of radiation
Radiation absorbed dose or radiation under investigation/
radiation absorbed dose of gamma or x-ray
Relates alpha or beta to gamma or x-ray
As an example: One alpha particle has the the RBE potential as 20 gamma rays
Related Linear Energy Transfer (LET), where LET is a function of charge and velocity. The greater the charge and the higher the velocity, the greater the LET and the RBE

REM (Roetgen Equivalent in Man)

Dose in RAD * Dose in RBE

Approximately equivalent to rad
Amount of radiation you are receiving
Analyzing amount of dose being absorbed by the body
Appears on a radiation report indicating the amount of radiation recieved by a radiation worker
100 RBE = Sv
A Sievert = QF x Gy
An RBE = QF x rad

General Comment: RBE, RAD, REM are all relatively equivalent to one another

Disintegrations Per Minute (dpm)

3.7 x 10¹⁰ dps = 1 Ci (per second)
2.2 x 10¹² dpm = 1 Ci (per minute)

What does dpm really mean? Pending the Ci amount of activity being measured, this value relates to the amount of gamma rays being emitted by the decaying radionuclide.
Specificially, if a source of radiation measures 1.0 mCi, then it is emitting 2.2 x 10⁹ gammas per minute. Over time the radionuclide decays and the amount of gamma rays or Ci value will decrease.
Usually the greater amount of activity translates to a shorter half-life. Consider the activity of a bone dose and a Cs137 source. Now relate this to their half-lives
This unit (Ci) is measured by a dose calibrator and is the unit used to measure the dose given to the patient.
Usually the amount administered to a patient is in the :Ci or mCi range
Example: A bone dose is normally 25 mCi of Tc99mMDP
Additional information on how to go between Bq and Ci will be given in the next lecture. For more informaiton link here.

Correlations Between DPM & CPM

Upake probes, well counters, and gamma cameras record counts in counts per minute or seconds (cpm or cps)
These instruments can never count all radiation being admitted from a radiation source. Why is this a true statement?
All radiation being admitted from the source would be measured in disintegrations per minute or second (dpm or dps).
Therefore, only a percentage of counts can be recorded by the limitation of any type of counting/imaging system. Hence, a scaler reads % of gamma rays in counts in either counts per minute (cpm) or counts per second (cps).c
To determine the amount of dpm being emited from a source the following formula must be applied:

Example: A uptake probe records 1000 cpm and has an 85% efficiency. What is the dpm?