First application of a high‐resolution silicon detector for proton beam Bragg peak detection in a 0.95 T magnetic field

Causer, Trent; Schellhammer, Sebastian; Gantz, Sebastian; Lühr, Armin; Hoffmann, Aswin L.; Metcalfe, Peter E; Rosenfeld, Anatoly B.; Guatelli, Susanna; Petasecca, Marco; Oborn, Bradley M

doi:10.1002/mp.13871

Cited by 4 publications

(5 citation statements)

References 27 publications

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“…Photon dosimetry in magnetic fields has been thoroughly investigated using both,dose measurements and Monte Carlo dose calculations to determine ionization chamber correction factors. [12][13][14][15][16] In comparison, proton dosimetry in magnetic fields is not yet established and it is under active development with investigations employing different complementary techniques, including Monte Carlo simulations, 17 radiochromic films, 18 semi-conductors, 19,20 and ionization chambers. 21 In particular, the findings by Fuchs et al showed that the magnetic field has a small but significant effect on the ionization chamber response (varying from −0.7% to 0.5%).…”

Section: Introductionmentioning

confidence: 99%

Proton beam dosimetry in the presence of magnetic fields using Farmer‐type ionization chambers of different radii

et al. 2023

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Background Magnetic resonance‐guided proton therapy is promising, as it combines high‐contrast imaging of soft tissue with highly conformal dose delivery. However, proton dosimetry in magnetic fields using ionization chambers is challenging since the dose distribution as well as the detector response are perturbed. Purpose This work investigates the effect of the magnetic field on the ionization chamber response, and on the polarity and ion recombination correction factors, which are essential for the implementation of a proton beam dosimetry protocol in the presence of magnetic fields. Methods Three Farmer‐type cylindrical ionization chambers, the 30013 with 3 mm inner radius (PTW, Freiburg, Germany) and two custom built chambers “R1” and “R6” with 1 and 6 mm inner radii respectively were placed at the center of an experimental electromagnet (Schwarzbeck Mess – Elektronik, Germany) 2 cm depth of an in‐house developed 3D printed water phantom. The detector response was measured for a 3 × 10 cm2 field of mono‐energetic protons 221.05 MeV/u for the three chambers, and with an additional proton beam of 157.43 MeV/u for the chamber PTW 30013. The magnetic flux density was varied between 0.1 and 1.0 Tesla in steps of 0.1 Tesla. Results At both energies, the ionization chamber PTW 30013 showed a non‐linear response as a function of the magnetic field strength, with a decrease of the ionization chamber response of up to 0.27% ± 0.06% (1 SD) at 0.2 Tesla, followed by a smaller effect at higher magnetic field strength. For the chamber R1, the response decreased slightly with the magnetic field strength up to 0.45% ± 0.12% at 1 Tesla, and for the chamber R6, the response decreased up to 0.54% ± 0.13% at 0.1 Tesla, followed by a plateau up to 0.3 Tesla, and a weaker effect at higher magnetic field strength. The dependence of the polarity and recombination correction factor on the magnetic field was ⩽0.1% for the chamber PTW 30013. Conclusions The magnetic field has a small but significant effect on the chamber response in the low magnetic field region for the chamber PTW 30013 and for R6, and in the high magnetic field region for the chamber R1. Corrections may be necessary for ionization chamber measurements, depending on both the chamber volume and the magnetic flux density. No significant effect of the magnetic field on the polarity and recombination correction factor was detected in this work for the ionization chamber PTW 30013.

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Section: Introductionmentioning

confidence: 99%

Proton beam dosimetry in the presence of magnetic fields using Farmer‐type ionization chambers of different radii

et al. 2023

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“…Correction factors have been derived to account for this, and depends on the magnetic field strength and directions 26–31 . For solid state‐based detectors, there is no apparent changes within the bulk of the detection volume, rather the diode packaging and any air‐gaps surrounding the diodes generate changes in the secondary electron fluence 32–35 …”

Section: Introductionmentioning

confidence: 99%

“…[26][27][28][29][30][31] For solid state-based detectors, there is no apparent changes within the bulk of the detection volume, rather the diode packaging and any air-gaps surrounding the diodes generate changes in the secondary electron fluence. [32][33][34][35] The purpose of the current work is to present the successful workings of a portable device capable of producing strong magnetic fields over a volume large enough to support fundamental small-scale experiments that mimic the environment of an MRI-linac system. The device is given the acronym MARDOS: Magnetic Apparatus for RaDiation Oncology Studies.…”

Section: Introductionmentioning

confidence: 99%

A portable magnet for radiation biology and dosimetry studies in magnetic fields

et al. 2022

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Background and Purpose In the current and rapidly evolving era of real‐time MRI‐guided radiotherapy, our radiation biology and dosimetry knowledge is being tested in a novel way. This paper presents the successful design and implementation of a portable device used to generate strong localized magnetic fields. These are ideally suited for small‐scale experiments that mimic the magnetic field environment inside an MRI‐linac system, or more broadly MRI‐guided particle therapy as well. Materials and Methods A portable permanent magnet‐based device employing an adjustable steel yoke and magnetic field focusing cones has been designed, constructed, and tested. The apparatus utilizes two banks of Nd2$_{2}$Fe14$_{14}$B permanent magnets totaling around 50 kg in mass to generate a strong magnetic field throughout a small volume between two pole tips. The yoke design allows adjustment of the pole tip gap and exchanging of the focusing cones. Further to this, beam portal holes are present in the yoke and focusing cones, allowing for radiation beams of up to 5 ×$\times$ 5 cm2$^{2}$ to pass through the region of high magnetic field between the focusing cone tips. Finite element magnetic modeling was performed to design and characterize the performance of the device. Automated physical measurements of the magnetic field components at various locations were measured to confirm the performance. The adjustable pole gap and interchangeable cones allows rapid changing of the experimental set‐up to allow different styles of measurements to be performed. Results A mostly uniform magnetic field of 1.2 T can be achieved over a volume of at least 3 ×$\times$ 3 ×$\times$ 3 cm3$^{3}$. This can be reduced in strength to 0.3 T but increased in volume to 10 ×$\times$ 10 ×$\times$ 10 cm3$^{3}$ via removal of the cone tips and/or adjustment of the steel yoke. Although small, these volumes are sufficient to house radiation detectors, cell culture dishes, and various phantom arrangements targeted at examining small radiation field dosimetry inside magnetic field strengths that can be changed with ease. Most important is the ability to align the magnetic field both perpendicular to, or inline with, the radiation beam. To date, the system has been successfully used to conduct published research in the areas of radiation detector performance, lung phantom dosimetry, and how small clinical electron beams behave in these strong magnetic fields. Conclusions A portable, relatively inexpensive, and simple to operate device has successfully been constructed and used for performing radiation oncology studies around the theme of MRI‐guided radiotherapy. This can be in either inline and perpendicular magnetic fields of up to 1.2 T with x‐ray and particle beams.

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“…The feasibility of integrating MRI-guidance for particle therapy, in terms of dosimetry, treatment planning and imaging, was recently demonstrated [6] , [7] , [8] , [9] .…”

Section: Introductionmentioning

confidence: 99%

An external perpendicular magnetic field does not influence survival and DNA damage after proton and carbon ion irradiation in human cancer cells

Gruber

Padilla‐Cabal

Mara

et al. 2022

Zeitschrift für Medizinische Physik

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First application of a high‐resolution silicon detector for proton beam Bragg peak detection in a 0.95 T magnetic field

Cited by 4 publications

References 27 publications

Proton beam dosimetry in the presence of magnetic fields using Farmer‐type ionization chambers of different radii

Proton beam dosimetry in the presence of magnetic fields using Farmer‐type ionization chambers of different radii

A portable magnet for radiation biology and dosimetry studies in magnetic fields

An external perpendicular magnetic field does not influence survival and DNA damage after proton and carbon ion irradiation in human cancer cells

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