MOSFET dosimetry with high spatial resolution in intense synchrotron-generated x-ray microbeams

Journal Article · Wed Apr 15 04:00:00 EDT 2009 · Medical Physics

DOI:https://doi.org/10.1118/1.3081934· OSTI ID:22095314

Siegbahn, E. A.; Braeuer-Krisch, E.; Bravin, A.; Nettelbeck, H.; Lerch, M. L. F.; Rosenfeld, A. B. ^[1]

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1. European Synchrotron Radiation Facility (ESRF), 6 Rue Jules Horowitz, 38043 Grenoble (France)

Various dosimeters have been tested for assessing absorbed doses with microscopic spatial resolution in targets irradiated by high-flux, synchrotron-generated, low-energy ({approx}30-300 keV) x-ray microbeams. A MOSFET detector has been used for this study since its radio sensitive element, which is extraordinarily narrow ({approx}1 {mu}m), suits the main applications of interest, microbeam radiation biology and microbeam radiation therapy (MRT). In MRT, micrometer-wide, centimeter-high, and vertically oriented swaths of tissue are irradiated by arrays of rectangular x-ray microbeams produced by a multislit collimator (MSC). We used MOSFETs to measure the dose distribution, produced by arrays of x-ray microbeams shaped by two different MSCs, in a tissue-equivalent phantom. Doses were measured near the center of the arrays and maximum/minimum (peak/valley) dose ratios (PVDRs) were calculated to determine how variations in heights and in widths of the microbeams influenced this for the therapy, potentially important parameter. Monte Carlo (MC) simulations of the absorbed dose distribution in the phantom were also performed. The results show that when the heights of the irradiated swaths were below those applicable to clinical therapy (<1 mm) the MC simulations produce estimates of PVDRs that are up to a factor of 3 higher than the measured values. For arrays of higher microbeams (i.e., 25 {mu}mx1 cm instead of 25x500 {mu}m{sup 2}), this difference between measured and simulated PVDRs becomes less than 50%. Closer agreement was observed between the measured and simulated PVDRs for the Tecomet MSC (current collimator design) than for the Archer MSC. Sources of discrepancies between measured and simulated doses are discussed, of which the energy dependent response of the MOSFET was shown to be among the most important.

• OSTI ID: 22095314
• Journal Information: Medical Physics, Journal Name: Medical Physics Journal Issue: 4 Vol. 36; ISSN 0094-2405; ISSN MPHYA6
• Country of Publication: United States
• Language: English

Related Subjects

61 RADIATION PROTECTION AND DOSIMETRY
COLLIMATORS
COMPUTERIZED SIMULATION
DOSEMETERS
DOSIMETRY
ENERGY DEPENDENCE
KEV RANGE 10-100
KEV RANGE 100-1000
MONTE CARLO METHOD
MOSFET
PHANTOMS
RADIATION DOSE DISTRIBUTIONS
RADIATION DOSES
RADIOBIOLOGY
RADIOTHERAPY
SPATIAL RESOLUTION
SYNCHROTRONS
X RADIATION