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Comparison of measured electron energy spectra for six matched, radiotherapy accelerators

This study compares energy spectra of the multiple electron beams of individual radiotherapy machines, as well as the sets of spectra across multiple matched machines. Also, energy spectrum metrics are compared with central‐axis percent depth‐dose (PDD) metrics. METHODS: A lightweight, permanent mag...

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Autores principales: McLaughlin, David J., Hogstrom, Kenneth R., Neck, Daniel W., Gibbons, John P.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: John Wiley and Sons Inc. 2018
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5978709/
https://www.ncbi.nlm.nih.gov/pubmed/29603874
http://dx.doi.org/10.1002/acm2.12317
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author McLaughlin, David J.
Hogstrom, Kenneth R.
Neck, Daniel W.
Gibbons, John P.
author_facet McLaughlin, David J.
Hogstrom, Kenneth R.
Neck, Daniel W.
Gibbons, John P.
author_sort McLaughlin, David J.
collection PubMed
description This study compares energy spectra of the multiple electron beams of individual radiotherapy machines, as well as the sets of spectra across multiple matched machines. Also, energy spectrum metrics are compared with central‐axis percent depth‐dose (PDD) metrics. METHODS: A lightweight, permanent magnet spectrometer was used to measure energy spectra for seven electron beams (7–20 MeV) on six matched Elekta Infinity accelerators with the MLCi2 treatment head. PDD measurements in the distal falloff region provided R (50) and R (80–20) metrics in Plastic Water(®), which correlated with energy spectrum metrics, peak mean energy (PME) and full‐width at half maximum (FWHM). RESULTS: Visual inspection of energy spectra and their metrics showed whether beams on single machines were properly tuned, i.e., FWHM is expected to increase and peak height decrease monotonically with increased PME. Also, PME spacings are expected to be approximately equal for 7–13 MeV beams (0.5‐cm R(90) spacing) and for 13–16 MeV beams (1.0‐cm R(90) spacing). Most machines failed these expectations, presumably due to tolerances for initial beam matching (0.05 cm in R (90); 0.10 cm in R (80–20)) and ongoing quality assurance (0.2 cm in R (50)). Also, comparison of energy spectra or metrics for a single beam energy (six machines) showed outlying spectra. These variations in energy spectra provided ample data spread for correlating PME and FWHM with PDD metrics. Least‐squares fits showed that R (50) and R (80–20) varied linearly and supralinearly with PME, respectively; however, both suggested a secondary dependence on FWHM. Hence, PME and FWHM could serve as surrogates for R (50) and R (80–20) for beam tuning by the accelerator engineer, possibly being more sensitive (e.g., 0.1 cm in R (80–20) corresponded to 2.0 MeV in FWHM). CONCLUSIONS: Results of this study suggest a lightweight, permanent magnet spectrometer could be a useful beam‐tuning instrument for the accelerator engineer to (a) match electron beams prior to beam commissioning, (b) tune electron beams for the duration of their clinical use, and (c) provide estimates of PDD metrics following machine maintenance. However, a real‐time version of the spectrometer is needed to be practical.
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spelling pubmed-59787092018-06-01 Comparison of measured electron energy spectra for six matched, radiotherapy accelerators McLaughlin, David J. Hogstrom, Kenneth R. Neck, Daniel W. Gibbons, John P. J Appl Clin Med Phys Radiation Oncology Physics This study compares energy spectra of the multiple electron beams of individual radiotherapy machines, as well as the sets of spectra across multiple matched machines. Also, energy spectrum metrics are compared with central‐axis percent depth‐dose (PDD) metrics. METHODS: A lightweight, permanent magnet spectrometer was used to measure energy spectra for seven electron beams (7–20 MeV) on six matched Elekta Infinity accelerators with the MLCi2 treatment head. PDD measurements in the distal falloff region provided R (50) and R (80–20) metrics in Plastic Water(®), which correlated with energy spectrum metrics, peak mean energy (PME) and full‐width at half maximum (FWHM). RESULTS: Visual inspection of energy spectra and their metrics showed whether beams on single machines were properly tuned, i.e., FWHM is expected to increase and peak height decrease monotonically with increased PME. Also, PME spacings are expected to be approximately equal for 7–13 MeV beams (0.5‐cm R(90) spacing) and for 13–16 MeV beams (1.0‐cm R(90) spacing). Most machines failed these expectations, presumably due to tolerances for initial beam matching (0.05 cm in R (90); 0.10 cm in R (80–20)) and ongoing quality assurance (0.2 cm in R (50)). Also, comparison of energy spectra or metrics for a single beam energy (six machines) showed outlying spectra. These variations in energy spectra provided ample data spread for correlating PME and FWHM with PDD metrics. Least‐squares fits showed that R (50) and R (80–20) varied linearly and supralinearly with PME, respectively; however, both suggested a secondary dependence on FWHM. Hence, PME and FWHM could serve as surrogates for R (50) and R (80–20) for beam tuning by the accelerator engineer, possibly being more sensitive (e.g., 0.1 cm in R (80–20) corresponded to 2.0 MeV in FWHM). CONCLUSIONS: Results of this study suggest a lightweight, permanent magnet spectrometer could be a useful beam‐tuning instrument for the accelerator engineer to (a) match electron beams prior to beam commissioning, (b) tune electron beams for the duration of their clinical use, and (c) provide estimates of PDD metrics following machine maintenance. However, a real‐time version of the spectrometer is needed to be practical. John Wiley and Sons Inc. 2018-03-30 /pmc/articles/PMC5978709/ /pubmed/29603874 http://dx.doi.org/10.1002/acm2.12317 Text en © 2018 The Authors. Journal of Applied Clinical Medical Physics published by Wiley Periodicals, Inc. on behalf of American Association of Physicists in Medicine. This is an open access article under the terms of the http://creativecommons.org/licenses/by/4.0/ License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
spellingShingle Radiation Oncology Physics
McLaughlin, David J.
Hogstrom, Kenneth R.
Neck, Daniel W.
Gibbons, John P.
Comparison of measured electron energy spectra for six matched, radiotherapy accelerators
title Comparison of measured electron energy spectra for six matched, radiotherapy accelerators
title_full Comparison of measured electron energy spectra for six matched, radiotherapy accelerators
title_fullStr Comparison of measured electron energy spectra for six matched, radiotherapy accelerators
title_full_unstemmed Comparison of measured electron energy spectra for six matched, radiotherapy accelerators
title_short Comparison of measured electron energy spectra for six matched, radiotherapy accelerators
title_sort comparison of measured electron energy spectra for six matched, radiotherapy accelerators
topic Radiation Oncology Physics
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5978709/
https://www.ncbi.nlm.nih.gov/pubmed/29603874
http://dx.doi.org/10.1002/acm2.12317
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