The Physics of Absorbed Dose and Linear Energy Transfer
The objectives of dosimetry and dose specification concern the description of the temporal and spatial distribution of the energy deposition at a macroscopic and microscopic level.
The incident radiation field is defined when the type of particles and their initial energy spectrum are specified. Knowledge of interaction coefficients is required to convert the particle fluence to energy imparted to biological tissue. The absorbed dose is defined as the differential quotient of mean energy imparted and mass. It is pointed out that the energy deposition is a stochastic process, and this becomes important if small doses and small volumes of tissue are considered.
The quality of the radiation can be related to the linear energy transfer spectra or the lineal energy spectra. Lineal energy spectra for different types of radiation are described and the expectation values: frequency mean lineal energy and dose mean lineal energy for neutrons of different energies are compared.
To explain the differences in biological effectiveness of different types of radiation, the energy deposition processes have to be correlated with the sizes of the biological structures involved. Some of the biophysical approaches to understand the biological effects of ionizing radiation are summarized.
KeywordsEnergy Deposition Neutron Energy Linear Energy Transfer Relative Biological Effectiveness Lineal Energy
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