Using a tungsten rollbar to characterize the source spot of a megavoltage bremsstrahlung linac
| Autor: | Clint M. Logan, A.E. Schach von Wittenau, R. D. Rikard |
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| Rok vydání: | 2002 |
| Předmět: |
Photon
Gaussian Physics::Medical Physics Monte Carlo method Sensitivity and Specificity Tungsten Linear particle accelerator law.invention Radiotherapy High-Energy symbols.namesake Optics law Dosimetry Computer Simulation Radiometry Physics business.industry Radiotherapy Planning Computer-Assisted Bremsstrahlung Particle accelerator General Medicine Models Theoretical Industrial radiography symbols Particle Accelerators Radioisotope Teletherapy business Monte Carlo Method |
| Zdroj: | Medical Physics. 29:1797-1806 |
| ISSN: | 2473-4209 0094-2405 |
| Popis: | In photon teletherapy, the size and functional form of the photon source spot affect both the sharpness of the penumbra of treatment fields and the sharpness of portal images. Photon source spot parameters are also used in photon teletherapy dose calculation codes. A simple method for characterizing the source spot would complement the existing, more involved methods that have been described in the medical physics literature. Such a method, using a rollbar made of tungsten or other high-Z metal, is used in industrial radiography. We describe the use of a tungsten rollbar for characterizing the source spot edge spread function (and thereby the source spot size and shape) of a megavoltage bremsstrahlung photon source. We use Monte Carlo simulations to quantify anticipated experimental artifacts of the method, assuming typical spot sizes for circ-function, Gaussian, and Bennett line shapes. We illustrate the use of the rollbar method by characterizing the source spot of a typical 9 MV linac used for industrial radiography. The source spot is analyzed using two approaches: (a) fitting the rollbar image with analytic functions and (b) using Abel inversion to obtain the cylindrically symmetric spot profile consistent with the measured rollbar image. Monte Carlo simulations, based on a 6 MV photon teletherapy accelerator, suggest that aspects of the method are applicable to medical bremsstrahlung sources. |
| Databáze: | OpenAIRE |
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