MOSFET dosimeters are seeing increased use for various dosimetry applications. Previously available commercial MOSFET dosimeters demonstrate significant anisotropies in the response when irradiated from certain directions at diagnostic x-ray energies. The angular response of a more recently introduced MOSFET dosimeter that claims an isotropic response to incident radiation is characterized. Measurements of the Thomson-Nielsen model TN-502RDI dosimeter were made for rotations of 360 degrees in 15 degrees increments about both the axial and normal-to-axial axes. These measurements demonstrated that the model TN-502RDI dosimeter has a nearly isotropic response at diagnostic x-ray energies with variations of less than 3% deviation from the mean response for radiation incident from most directions. Only two specific orientations showed significant deviation from the overall isotropic response. These correspond to the exposure scenarios where radiation is incident directly along the axis where the wire leads attach to the MOSFET device and the distal tip, the 90 degrees and 270 degrees orientations for normal-to-axial rotations, respectively. The largest deviations from an isotropic response occur when the dosimeter is irradiated free-in-air. Irradiations performed at the center of a tissue equivalent cylinder resulted in smaller deviations in angular response. The improved angular response of the TN-502RDI allows greater freedom in placement and use of MOSFET dosimeters in diagnostic radiology applications.
Pediatric radiographic examinations yield medical benefits and/or diagnostic information that must be balanced against potential risk from patient radiation exposure. Consequently, clinical tools for measuring internal organ dose are needed for medical risk assessment. In this study, a physical phantom and Monte Carlo simulation model of the newborn patient were developed based upon their stylized mathematical expressions (ORNL and MIRD model series). The physical phantom was constructed using tissue equivalent substitutes for soft tissue, lung, and skeleton. Twenty metal-oxide-semiconductor field effect transistor (MOSFET) dosimeters were then inserted at three-dimensional positions representing the centroids of organs assigned in the ICRP's definition of the effective dose. MOSFET-derived point estimates of organ dose were shown to be in reasonable agreement with Monte Carlo estimates for representative newborn head, chest, and abdomen radiographic exams. Ratios of average organ dose assessed via MCNP simulations to the MOSFET-derived point doses (point-to-organ dose scaling factors, SF(POD)) are tabulated for subsequent use in clinical irradiations of the newborn phantom/MOSFET system. Values of SF(POD) indicate that MOSFET measurements of point dose for in-field exposures need to be adjusted only to within 10% to report volume-averaged organ dose. Larger adjustments to point doses are noted for organs out-of-field. For walled organs, point estimates of organ dose at the content centroid are shown to underestimate the average wall dose when the organ is within the primary field: SF(POD) of 1.19 for the stomach (AP chest exam), and SF(POD) of 1.15 for the urinary bladder (AP abdomen exam).
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.