TY - JOUR
T1 - On the biological basis for competing macroscopic dose descriptors for kilovoltage dosimetry
T2 - Cellular dosimetry for brachytherapy and diagnostic radiology
AU - Thomson, R. M.
AU - Tedgren, Å Carlsson
AU - Williamson, J. F.
PY - 2013/2/21
Y1 - 2013/2/21
N2 - The purpose of this work is to investigate how alternative macroscopic dose descriptors track absorbed dose to biologically relevant subcellular targets via Monte Carlo (MC) analysis of cellular models for a variety of cancerous and normal soft tissues for kilovoltage radiation. The relative mass distributions of water, light inorganic elements, and protein components of nuclear and cytoplasm compartments for various tissues are determined from a literature review. These data are used to develop representative cell models to demonstrate the range of mass elemental compositions of these subcellular structures encountered in the literature from which radiological quantities (energy absorption and attenuation coefficients; stopping powers) are computed. Using representative models of cell clusters, doses to subcellular targets are computed using MC simulation for photon sources of energies between 20 and 370 keV and are compared to bulk medium dose descriptors. It is found that cells contain significant and varying mass fractions of protein and inorganic elements, leading to variations in mass energy absorption coefficients for cytoplasm and nuclear media as large as 10% compared to water for sub-50 keV photons. Doses to subcellular structures vary by as much as 23% compared to doses to the corresponding average bulk medium or to small water cavities embedded in the bulk medium. Relationships between cellular target doses and doses to the bulk medium or to a small water cavity embedded in the bulk medium are sensitive to source energy and cell morphology, particularly for lower energy sources, e.g., low energy brachytherapy (<50 keV). Results suggest that cells in cancerous and normal soft tissues are generally not radiologically equivalent to either water or the corresponding average bulk tissue. For kilovoltage photon sources, neither dose to bulk medium nor dose to water quantitatively tracks energy imparted to biologically relevant subcellular targets for the range of cellular morphologies and tissues considered.
AB - The purpose of this work is to investigate how alternative macroscopic dose descriptors track absorbed dose to biologically relevant subcellular targets via Monte Carlo (MC) analysis of cellular models for a variety of cancerous and normal soft tissues for kilovoltage radiation. The relative mass distributions of water, light inorganic elements, and protein components of nuclear and cytoplasm compartments for various tissues are determined from a literature review. These data are used to develop representative cell models to demonstrate the range of mass elemental compositions of these subcellular structures encountered in the literature from which radiological quantities (energy absorption and attenuation coefficients; stopping powers) are computed. Using representative models of cell clusters, doses to subcellular targets are computed using MC simulation for photon sources of energies between 20 and 370 keV and are compared to bulk medium dose descriptors. It is found that cells contain significant and varying mass fractions of protein and inorganic elements, leading to variations in mass energy absorption coefficients for cytoplasm and nuclear media as large as 10% compared to water for sub-50 keV photons. Doses to subcellular structures vary by as much as 23% compared to doses to the corresponding average bulk medium or to small water cavities embedded in the bulk medium. Relationships between cellular target doses and doses to the bulk medium or to a small water cavity embedded in the bulk medium are sensitive to source energy and cell morphology, particularly for lower energy sources, e.g., low energy brachytherapy (<50 keV). Results suggest that cells in cancerous and normal soft tissues are generally not radiologically equivalent to either water or the corresponding average bulk tissue. For kilovoltage photon sources, neither dose to bulk medium nor dose to water quantitatively tracks energy imparted to biologically relevant subcellular targets for the range of cellular morphologies and tissues considered.
UR - http://www.scopus.com/inward/record.url?scp=84873663102&partnerID=8YFLogxK
U2 - 10.1088/0031-9155/58/4/1123
DO - 10.1088/0031-9155/58/4/1123
M3 - Article
C2 - 23363781
AN - SCOPUS:84873663102
SN - 0031-9155
VL - 58
SP - 1123
EP - 1150
JO - Physics in medicine and biology
JF - Physics in medicine and biology
IS - 4
ER -