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Feasibility of kilovoltage x‐ray energy modulation by gaseous media and its application in contrast‐enhanced radiotherapy
Author(s) -
FacundoFlores E. L.,
GarnicaGarza H. M.
Publication year - 2013
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4818422
Subject(s) - spectral line , x ray , optics , beam (structure) , radiation , materials science , spectrometer , energy (signal processing) , basis function , physics , quantum mechanics , astronomy
Purpose: To present a method to modulate the energy contents of a kilovoltage x‐ray beam that makes use of a gas as the modulating medium. The method is capable of producing arbitrary x‐ray spectra by varying the pressure of the modulating gas and the peak kilovoltage (kVp) of the x‐ray beams whose energy is being modulated.Methods: An aluminum chamber was machined with a 0.5 cm wall thickness, designed to withstand pressures of more than 80 atm. A pressure sensor and electrovalves were used to monitor and regulate the gas pressure. Argon was used as the modulating gas. A CdTe spectrometer was used to measure x‐ray spectra for different combinations of kVp and gas pressure, thus obtaining a set of basis x‐ray functions. An arbitrary x‐ray spectrum can then be formed by the linear combination of such basis functions. In order to show one possible application of the modulation method, a contrast‐enhanced radiotherapy prostate treatment was optimized with respect to the x‐ray beam energy, without restrictions on the possible shape of the resultant x‐ray spectra.Results: The x‐ray spectra basis functions obtained display a smooth and gradual variation of their average energy as a function of the gas pressure for a given kVp, sometimes in the order of 1 or 2 keV. This gradual variation would be difficult to obtain with a conventional aluminum or copper filters, as the change in thickness necessary to reproduce the data presented would be in the order of micrometers, making necessary the use of a large number of such filters. Using the modulation method presented here, the authors were able to reconstruct the optimized x‐ray spectra from the measured basis functions, for different optimization objectives.Conclusions: A method has been developed that allows for the controlled modulation of the energy contents of kilovoltage x‐ray spectra. The method has been shown to be able to reproduce spectra of arbitrary shape, such as those obtained from the optimization of contrast‐enhanced radiotherapy. The method may have other applications as well, such as in the precise matching of diagnostic x‐ray catalog spectra.