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Basic dosimetry and beam-quality characterization
Published in Gavin Poludniowski, Artur Omar, Pedro Andreo, Calculating X-ray Tube Spectra, 2022
Gavin Poludniowski, Artur Omar, Pedro Andreo
The dosimetry of photons with energies up to about 300 keV is governed by the quantity kerma, which accounts for the transfer of the kinetic energy of photon-produced electrons to a volume of material. Kerma is the acronym for kinetic energy released per unit mass and has the unit of gray (Gy). It can be shown [65] that in a given medium, kerma is related to the field quantities fluence and energy fluence through K=kΦmedμtrkρmed=Ψmedμtrkρmed,
Quality Assurance of X-ray Computer Tomography
Published in Paolo Russo, Handbook of X-ray Imaging, 2017
In addition to making sure the dose level remains within tolerance, the quality of the radiation should also be periodically tested to ensure the continuing quality of the device. This can be done through measuring the kVp and the half-value layer (HVL) of the emitted radiation. The tests to measure these quantities are described in greater detail in Section 37.5. Other quantities such as timer accuracy, exposure linearity, and radiation profile can also impact the dose a patient receives and so a discussion of how to measure those is also included. Finally, it is not just dose to the patient that is of concern but also the potential exposure of staff members and people in surrounding rooms. During the initial design of the room, adequate shielding must be put in place to keep the kerma in both controlled and uncontrolled (locations to which non-radiation workers have access) areas below acceptable thresholds. These are typically considered less than 0.02 mGy wk−1 and 0.1 mGy wk−1, respectfully. A more detailed discussion of CT shielding calculation is beyond the scope of this chapter and interested readers are referred to National Council on Radiation Protection and Measurements (NCRP) report 147 (Korchin 2005). Part of QA for the safety of the CT scanner, however, involves surveying the neighboring rooms to the scanner to ensure that the shielding has been adequately constructed, and a more detailed discussion of this can be found in Section 37.6.
K
Published in Splinter Robert, Illustrated Encyclopedia of Applied and Engineering Physics, 2017
[biomedical, energy] (also “collision Kerma”) Acronym for “kinetic energy released in the medium,” in radiation therapy this indicates the hypothetical potential for the biological effect caused by radiation delivered at locations r→ in direction s→ with respect to the surface of an absorbing volume. The Kerma dose (Kc) is a direct function of the fluence L→(r→,s→) of photons with energy E that can be transferred to kinetic energy of charged particles in the medium (Etransfered) that can have ionizing effects (e.g., electrons and protons), with respect to the energy delivered per unit mass (m):Dc = ΔEtransfered/m. The Kerma is different from the absorbed in the fact that the Kerma describes the energy transferred between the radiation applied and the medium the radiation is migrating through, no absorption of radiation is assumed. Kerma is expressed in gray:[Gy] = 1J/kg = 100 rad. Kerma is different from “radiation exposure.”
Prompt Radiation Dose Analysis Within the European Spallation Source Connection Cell
Published in Nuclear Science and Engineering, 2023
When using the KERMA approximation to estimate absorbed dose, one assumes that the material volume in which the absorbed dose is being calculated is in charged particle equilibrium and that the energy of all charged particles produced is deposited locally (i.e., where the charged particle was produced). This is typically a conservative result. As the material volume becomes small and the energy of particles increases, this assumption breaks down. Fortunately for this analysis, when the assumption of charged particle equilibrium breaks down, the KERMA approximation usually results in a larger dose than the actual absorbed dose. Considering that the actual materials being analyzed were not included in the geometry model, one cannot assume charged particle equilibrium was satisfied. For small components in the connection cell, especially electronics, the results produced by this methodology are likely conservative.
Dosimetric effect of carbon fiber treatment couch in boron neutron capture therapy
Published in Journal of Nuclear Science and Technology, 2023
Yongquan Wang, Huangxin Wu, Junliang Du, Jinyang Li, Xingcai Guan, Long Gu
where is the kinetic energy released in the matter (Kerma) factor for neutrons or dose conversion factor for photons and is the flux of neutrons or photons. In this study, the default cross-section library JENDL-4.0 [18,19] used in PHITS for transport calculation was changed to the ENDF/B-VIII cross-section library. This was done in order to maintain consistency with the nuclear database used in the previous work [12]. The Kerma factor value was calculated using the ENDF/B-VIII. Figure 6 shows the Kerma factor with a 100% mass percentage of atomic 10B, 1H, and 14N. The absorbed dose between neutrons and corresponding atoms in each voxel can be calculated by using the Kerma factor. Then the absorbed dose can be scaled according to the actual atomic mass percentage of 10B, 1H, and 14N in each voxel. For photons, the Kerma factor is calculated according to the actual element composition of 27 materials, as shown in Figure 7. Only the absorbed dose in the human body is concerned, so Kerma factors for air materials (Group 1) are not calculated.
Buildup with Bremsstrahlung in the Martian Atmosphere
Published in Nuclear Science and Engineering, 2021
Praneel P. Gulabrao, Kevin T. Clarno
where the mass energy transfer coefficient is multiplied by photon energy fluence ( where is the photon flux and E is the photon energy). Furthermore, to ensure KERMA is a good approximation of absorbed dose, “the production of Bremsstrahlung can be taken into account by the substitution of ” for . The linear energy absorption coefficient is defined as