Absorbed Dose: Rad and Gray

Study Notes

Absorbed Dose: Rad and Gray

Introduced by ICRU in 1962, the rad (r) is a unit of absorbed dose.
1 rad equals 100 ergs per gram, independent of radiation type and medium.
Radiation exposure leads to energy transfer defined as kerma, but some energy may not be absorbed due to bremsstrahlung and delta rays.
Absorbed dose calculation: Absorbed dose = Kerma - bremsstrahlung X-rays.
The SI unit for absorbed dose is gray (Gy), defined as 1 Gy = J/kg = 10^7 erg.
Conversion: 1 Gy = 100 rads; common submultiples include:
- 1 milligray (mGy) = 10^-3 Gy
- 1 microgray (µGy) = 10^-6 Gy.
Relationships: 1 mGy = 100 mrad; 1 µGy = 100 urad.
Rad or gray units describe energy delivered to the medium and are suitable for quantifying biological effects in patients.

Roentgen-to-Rad Conversion

The absorbed dose (D) relates to roentgen through a conversion factor (f) specific to materials.
F-factor values vary with photon energy (in keV) and material type (specifically for fat, air, and muscle):
- 30 keV: f = 0.53
- 50 keV: f = 0.64
- 100 keV: f = 0.58
- 150 keV: f = 0.53

Conversion of Exposure to Absorbed Dose

Dose in air (Dair) relates to the charge of 1 roentgen, which is 2.58 × 10^-4 Coulombs/kg.
Average energy for a photon causing this charge is approximately 33 J.
Total energy absorbed per kilogram of air equates to 8.5 × 10^-3 J/kg, numerically equal to 1 roentgen.

Description

This quiz covers the concepts of absorbed dose, focusing on the units rad and gray, as introduced by ICRU in 1962. It addresses the calculations and conversions between different units and explores their significance in radiation exposure and biological effects. Test your understanding of the relationships between energy transfer, kerma, and absorbed dose.