Permanent‐magnet energy spectrometer for electron beams from radiotherapy accelerators

McLaughlin, D.J.; Hogstrom, Kenneth R.; Carver, Robert L.; Gibbons, John; Shikhaliev, Polad M.; Matthews, K.; Clarke, Taylor; Henderson, Alexander; Liang, Edison

doi:10.1118/1.4928674

Cited by 6 publications

(6 citation statements)

References 21 publications

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“…Based on the results of the present study, we conclude that a lightweight, permanent magnet spectrometer1 is a useful tool for measuring energy spectra of matched therapeutic electron beams, allowing their comparison and evaluation, both qualitatively and quantitatively. Comparison of energy spectra for all beams on a single accelerator in most cases showed that the PME and FWHM of the energy spectra did not always smoothly vary monotonically with beam energy, as otherwise expected.…”

Section: Summary and Recommendationsmentioning

confidence: 55%

“…For each machine, energy spectra were measured for all energies on a single day using the permanent magnet spectrometer previously fabricated by Rice University (Houston, TX) and described by McLaughlin et al 1. The energy spectra were measured for that portion of the electron beams on central‐axis at 95‐cm SCD, which passes through a 0.278‐cm diameter aperture in a 1.59‐cm thick Cerrobend collimating insert placed in the 14 × 14 cm 2 applicator (cf Fig.…”

Section: Methodsmentioning

confidence: 99%

“…The electrons passed downstream through a second 0.318‐cm diameter pinhole copper collimator after which the magnetic field bent the electrons onto a CR strip, which recorded intensity vs position. Subsequent readout of the CR strips produced intensity vs position curves that were converted into energy spectra using methods previously described by McLaughlin et al 1. All energy spectra plotted in this study were normalized to have an area of unity.…”

Section: Methodsmentioning

confidence: 99%

“…for the measurement of energy spectra of therapeutic electron beams 1. The 4‐kg spectrometer (16.5 cm long by 5.3 cm wide by 7.8 cm high) contains a dipole, neodymium permanent magnet with a 1.43 cm air separation, producing a 0.54 T field.…”

Section: Introductionmentioning

confidence: 99%

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

McLaughlin

Hogstrom

Neck

et al. 2018

J Applied Clin Med Phys

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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.MethodsA 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).ResultsVisual 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 R90 spacing) and for 13–16 MeV beams (1.0‐cm R90 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).ConclusionsResults 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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Section: Summary and Recommendationsmentioning

confidence: 55%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

McLaughlin

Hogstrom

Neck

et al. 2018

J Applied Clin Med Phys

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“…There is a considerable interest in the magnetic systems on the base of rare-earth permanent magnets for use in special accelerators such as medical and technological accelerators, microtrons, liner colliders and etc [1][2][3][4][5]. The creation of each such device is associated with the need to take into account the parameters of accelerators and the features of their operation.…”

Section: Introductionmentioning

confidence: 99%

RARE-EARTH PERMANENT MAGNET IN MAGNETIC SYSTEM OF ELECTRON ACCELERATOR WITH THE ENERGY OF 10 MеV

Bovda¹,

Bovda²,

Guk³

et al. 2019

Problems of Atomic Science and Technology

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New algorithm using L1 regularization for measuring electron energy spectra

Sakaki

Yamashita

Akagi

et al. 2020

Review of Scientific Instruments

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Retrieving the spectrum of physical radiation from experimental measurements typically involves using a mathematical algorithm to deconvolve the instrument response function from the measured signal. However, in the field of signal processing known as “Source Separation” (SS), which refers to the process of computationally retrieving the separate source components that generate an overlapping signal on the detector, the deconvolution process can become an ill-posed problem and crosstalk complicates the separation of the individual sources. To overcome this problem, we have designed a magnetic spectrometer for inline electron energy spectrum diagnosis and developed an analysis algorithm using techniques applicable to the problem of SS. An unknown polychromatic electron spectrum is calculated by sparse coding using a Gaussian basis function and an L1 regularization algorithm with a sparsity constraint. This technique is verified by using a specially designed magnetic field electron spectrometer. We use Monte Carlo simulations of the detector response to Maxwellian input energy distributions with electron temperatures of 5.0 MeV, 10.0 MeV, and 15.0 MeV to show that the calculated sparse spectrum can reproduce the input spectrum with an optimum energy bin width automatically selected by the L1 regularization. The spectra are reproduced with a high accuracy of less than 4.0% error, without an initial value. The technique is then applied to experimental measurements of intense laser accelerated electron beams from solid targets. Our analysis concept of spectral retrieval and automatic optimization of energy bin width by sparse coding could form the basis of a novel diagnostic method for spectroscopy.

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Permanent‐magnet energy spectrometer for electron beams from radiotherapy accelerators

Cited by 6 publications

References 21 publications

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

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

RARE-EARTH PERMANENT MAGNET IN MAGNETIC SYSTEM OF ELECTRON ACCELERATOR WITH THE ENERGY OF 10 MеV

New algorithm using L1 regularization for measuring electron energy spectra

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