Magnetic fields with photon beams: Dose calculation using electron multiple‐scattering theory

Jette, David

doi:10.1118/1.1286554

Cited by 30 publications

(17 citation statements)

References 24 publications

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“…The dose reduction is due to the loss of transient charged particle equilibrium downstream from the magnetic field. Jette [6,7] confirmed this effect by using electron multiple‐scattering theory and Monte Carlo calculations. Li et al [8] also demonstrated the effect along the central axis of the radiation beam using idealized step, ramp, and dipole fields.…”

Section: Introductionmentioning

confidence: 90%

Modulation of radiotherapy photon beam intensity using magnetic field The views, opinions, and/or findings contained in this report are those of the authors and should not be construed as a position, policy, decision, or endorsement of the federal government or the NMTB.

Chu

Reiffel²,

Hsi

et al. 2001

Int. J. Cancer

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SUMMARY The purpose of this study was to explore the potential advantages of using strong magnetic fields to increase tumor dose and to decrease normal tissue dose in radiation therapy. Strong magnetic fields are capable of altering the trajectories of charged particles. A magnetic field applied perpendicularly to the X-ray beam forces the secondary electrons and positrons to spiral and produces a dose peak. The same magnetic field also prevents the electrons and positrons from traveling downstream and produces a lower dose region distal to the dose peak. The locations of these high-and low-dose regions are potentially adjustable to enhance the dose to the target volume and decrease the dose to normal tissues. We studied this effect using the Monte Carlo simulation technique. The EGS4 code was used to simulate the effect produced by a coil magnet currently under construction. The coil magnet is designed to support up to 350 A operating current and 15 T peak field on windings. Dose calculations in a water phantom show that the transverse magnetic field produces significant dose effects along the beam direction of radiation therapy X-rays. Depending on the beam orientation, the radiation dose at different depths along the beam can be increased or reduced. This dose effect varies with photon energy, field size, magnetic field strength, and relative magnet/beam geometry. The off-axis beam profiles also show considerable skewness under the influence of the magnetic field. The magnetic field-induced dose shift may result in high dose regions outside the geometrical boundary of the initial radiation beam. We have demonstrated that current or near-term magnet technology is capable of producing significant dose enhancement and reduction in radiation therapy photon beams. This technology should be further developed to improve our ability to deliver higher doses to the tumor and lower doses to normal tissues in radiation therapy.

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Section: Introductionmentioning

confidence: 90%

Modulation of radiotherapy photon beam intensity using magnetic field The views, opinions, and/or findings contained in this report are those of the authors and should not be construed as a position, policy, decision, or endorsement of the federal government or the NMTB.

Chu

Reiffel²,

Hsi

et al. 2001

Int. J. Cancer

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“…14 -16 To keep up with the experimental work, Jette 17 has recently worked out the general equation of motion of a particle traveling in a material under the influence of a magnetic field. The continuous slowing down approximation and multiple scattering were included.…”

Section: Current and Future Workmentioning

confidence: 99%

Evaluating the effectiveness of a longitudinal magnetic field in reducing underdosing of the regions around upper respiratory cavities irradiated with photon beams—A Monte Carlo study

2001

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The problem of underdosing lesions adjacent to upper respiratory cavities and a proposal to correct it are presented in this work. The EGS4 Monte Carlo code was used to simulate a 6 MV x-ray beam passing through a block of tissues with air cavities 2, 4, and 6 cm wide. The geometry used approximates the tracheal geometry used by previous researchers who investigated the underdosing phenomenon. A uniform longitudinal magnetic field of 0.5 T strength is used to reduce secondary electron outscatter caused by the presence of an air gap, and thus improving the dose at the distal surface of air cavities. We introduce the term "percent dose reduction" (PDR), which is defined as the difference between the dose after the air cavity and the dose at the same depth in soft-tissue phantom normalized to the dose in the tissue phantom, to quantify the reduction in dose after an air gap. We also introduce the term dose improvement ratio (DIR), which is defined as the dose ratio with magnetic field to the dose, at the same point, without magnetic field, to quantify the improvement in dose when the magnetic field is applied. For 2 x 2 x 20 cm3 and 4 x 4 x 20 cm3 air cavities irradiated by 2 x 2 cm2 beams, we found PDRs of 38% and 52%, respectively. This means that for these cavities, there is a 38% and a 52% reduction in dose at the cavity edge compared to the same dose in tissue at the same depth for each cavity. The dose improved by 30% (DIR= 1.3) and 87% (DIR= 1.87), respectively, when applying the magnetic field. The worst effect on dose at the distal side came from larger cavities irradiated with small fields. In these situations, the improvement in dose due to the presence of magnetic field was the largest. This article deals with "ideal" head and neck geometries with a uniform magnetic field. In a paper to follow we will use a CT-based phantom to study the effect in realistic geometries with the presence of a magnetic field from a Helmholtz coil pair.

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“…Suppose a patient is irradiated by a photon beam in the presence of a magnetic field with a strong transverse component. From previous work [1][2][3] we know that, if the magnetic field has appropriate characteristics, its addition can create very large dose enhancements in localized regions, as well as large dose reductions distal to the enhanced-dose region. In Ref.…”

Section: Introductionmentioning

confidence: 99%

Magnetic fields with photon beams: Planar-current-induced magnetic fields

Jette

2003

Med. Phys.

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Strong transverse magnetic fields can produce very large dose enhancements and reductions in localized regions of a patient under irradiation by a photon beam. In this work we consider planar-current-induced magnetic fields ("PCIMFs") generated by arbitrary electric currents in one or two parallel planes, and pose two questions: how much arbitrariness is there in specifying a PCIMF, and how can we solve the "inverse problem" of determining the current distribution which generates a chosen PCIMF? We have completely answered both questions, and have applied the general formulas which we have developed to the case of cylindrical symmetry, giving a concrete example of our method. The present work provides the theoretical tools for designing PCIMFs, but a great deal of systematic research will be required in order to understand and design magnetic fields which produce desired distributions of dose enhancement and dose reduction in photon beams treating patients.

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Magnetic fields with photon beams: Dose calculation using electron multiple‐scattering theory

Cited by 30 publications

References 24 publications

Modulation of radiotherapy photon beam intensity using magnetic field The views, opinions, and/or findings contained in this report are those of the authors and should not be construed as a position, policy, decision, or endorsement of the federal government or the NMTB.

Modulation of radiotherapy photon beam intensity using magnetic field The views, opinions, and/or findings contained in this report are those of the authors and should not be construed as a position, policy, decision, or endorsement of the federal government or the NMTB.

Evaluating the effectiveness of a longitudinal magnetic field in reducing underdosing of the regions around upper respiratory cavities irradiated with photon beams—A Monte Carlo study

Magnetic fields with photon beams: Planar-current-induced magnetic fields

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