Nonetheless kerma plays an important role in radiation dosimetry because it is the energy released per unit mass of material, and not surprisingly this is closely related to the energy absorbed per unit mass of material. In fig 1 the absorbed dose sums the energy deposition on all the tracks from P to P . For volumes which are large compared to the tracklength, the kerma and absorbed dose are virtually identical, especially since absorbed dose also includes energy deposition within the volume by electrons set in motion outside the volume. This tends to balance the energy deposited outside the volume by those electrons starting inside the volume. Absorbed dose is currently taken as the best physical indicator of biological response.
Absorbed dose has the further advantage that it is directly measurable in a variety of ways.
The most straightforward is by calorimetry which determines the energy deposited per unit mass of material by measuring the temperature rise.