Dose to tissue medium or water cavities as surrogate for the dose to cell nuclei at brachytherapy photon energies.
Summary of "Dose to tissue medium or water cavities as surrogate for the dose to cell nuclei at brachytherapy photon energies."
It has been suggested that modern dose calculation algorithms should be able to report absorbed dose both as dose to the local medium, D(m,m,) and as dose to a water cavity embedded in the medium, D(w,m), using conversion factors from cavity theory. Assuming that the cell nucleus with its DNA content is the most important target for biological response, the aim of this study is to investigate, by means of Monte Carlo (MC) simulations, the relationship of the dose to a cell nucleus in a medium, D(n,m,) to D(m,m) and D(w,m), for different combinations of cell nucleus compositions and tissue media for different photon energies used in brachytherapy. As D(n,m) is very impractical to calculate directly for routine treatment planning, while D(m,m) and D(w,m) are much easier to obtain, the questions arise which one of these quantities is the best surrogate for D(n,m) and which cavity theory assumptions should one use for its estimate. The Geant4.9.4 MC code was used to calculate D(m,m,) D(w,m) and D(n,m) for photon energies from 20 (representing the lower energy end of brachytherapy for (103)Pd or(125)I) to 300 keV (close to the mean energy of (192)Ir) and for the tissue media adipose, breast, prostate and muscle. To simulate the cell and its nucleus, concentric spherical cavities were placed inside a cubic phantom (10 × 10 × 10 mm(3)). The diameter of the simulated nuclei was set to 14 µm. For each tissue medium, three different setups were simulated; (a) D(n,m) was calculated with nuclei embedded in tissues (MC-D(n,m)). Four different published elemental compositions of cell nuclei were used. (b) D(w,m) was calculated with MC (MC-D(w,m)) and compared with large cavity theory calculated D(w,m) (LCT-D(w,m)), and small cavity theory calculated D(w,m) (SCT-D(w,m)). (c) D(m,m) was calculated with MC (MC-D(m,m)). MC-D(w,m) is a good substitute for MC-D(n,m) for all photon energies and for all simulated nucleus compositions and tissue types. SCT-D(w,m) can be used for most energies in brachytherapy, while LCT-D(w,m) should only be considered for source spectra well below 50 keV, since contributions to the absorbed dose inside the nucleus to a large degree stem from electrons released in the surrounding medium. MC-D(m,m) is not an appropriate substitute for MC-D(n,m) for the lowest photon energies for adipose and breast tissues. The ratio of MC-D(m,m) to MC-D(n,m) for adipose and breast tissue deviates from unity by 34% and 15% respectively for the lowest photon energy (20 keV), whereas the ratio is close to unity for higher energies. For prostate and muscle tissue MC-D(m,m) is a good substitute for MC-D(n,m). However, for all photon energies and tissue types the nucleus composition with the highest hydrogen content behaves differently than other compositions. Elemental compositions of the tissue and nuclei affect considerably the absorbed dose to the cell nuclei for brachytherapy sources, in particular those at the low-energy end of the spectrum. Thus, there is a need for more accurate data for the elemental compositions of tumours and healthy cells. For the nucleus compositions and tissue types investigated, MC-D(w,m) is a good substitute to MC-D(n,m) for all simulated photon energies. Whether other studied surrogates are good approximations to MC-D(n,m) depends on the target size, target composition, composition of the surrounding tissue and photon energy.
Université Laval, Centre Hospitalier Universitaire de Quebec, Centre de recherche de L'Hôtel-Dieu de Québec, Quebec, Canada.
This article was published in the following journal.
Name: Physics in medicine and biology
- PubMed Source: http://www.ncbi.nlm.nih.gov/pubmed/22722477
- DOI: http://dx.doi.org/10.1088/0031-9155/57/14/4489
Medical and Biotech [MESH] Definitions
Lethal Dose 50
The dose amount of poisonous or toxic substance or dose of ionizing radiation required to kill 50% of the tested population.
Dose-response Relationship, Immunologic
A specific immune response elicited by a specific dose of an immunologically active substance or cell in an organism, tissue, or cell.
Maximum Tolerated Dose
The highest dose of a biologically active agent given during a chronic study that will not reduce longevity from effects other than carcinogenicity. (from Lewis Dictionary of Toxicology, 1st ed)
Administration of the total dose of radiation (RADIATION DOSAGE) in parts, at timed intervals.
Dose-response Relationship, Radiation
The relationship between the dose of administered radiation and the response of the organism or tissue to the radiation.
Model-based dose calculation algorithms (MBDCAs), recently introduced in treatment planning systems (TPS) for brachytherapy, calculate tissue absorbed doses. In the TPS framework, doses have hereto be...
The Monte Carlo method enables accurate dose calculation for radiation therapy treatment planning and has been implemented in some commercial treatment planning systems. Unlike conventional dose calcu...
The purpose of this study is to determine whether dose to medium, D(m), or dose to water, D(w), provides a better estimate of the dose to the radiosensitive red bone marrow (RBM) and bone surface cell...
Nasopharyngeal tumors are commonly treated with intensity-modulated radiotherapy techniques. For photon dose calculations, problems related to loss of lateral electronic equilibrium exist when small f...
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 model...
The purpose of this study is to control the levels of bacteria that causes cavities in mothers by a combination of treatments that include fluoride and chlorhexidine varnishes and xylitol-...
To evaluate the safety and efficacy of PF-04217329.
To compare the efficacy of combination therapy of montelukast plus low dose inhaled budesonide and single therapy of medium dose inhaled budesonide on asthma control such as inflammatory m...
The proposed study will evaluate the safety, tolerability, pharmacokinetics (PK) and pharmacodynamics of repeated oral doses of GSK618334 in healthy male and female volunteers.
The primary objective of this study is to compare the three study arms of lower, medium, and higher dose platelet therapy with respect to the percentage of patients experiencing at least o...