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

Wadi-Ramahi, Shada; Naqvi, S; Chu, James C.H.

doi:10.1118/1.1386780

Cited by 15 publications

(8 citation statements)

References 13 publications

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“…However, the magnetic field effect on photon beams was not reported until some 40 years later, when Bielajew [2] showed reduction of the penumbral width using strong longitudinal magnetic fields. A modest longitudinal magnetic field was also shown to minimize potential target underdosing for tumors located in or near low‐density regions such as the lung or trachea [3,4].…”

Section: Introductionmentioning

confidence: 99%

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: 99%

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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“…Although some scholars advocate adjustment of the radiation dose, (27) most advocate irradiation from two fields or irradiation with the same center from several fields instead. The latter methods allow variation of dose to be reduced to 4%, which meets the requirement (Report ICRU 24) that the total uncertainty of dose in the target region must be less than 5% 21 , 28 , 29 . In order to reduce the influence of metal implants on the dose of radiation therapy, the treatment planning system (TPS) is usually employed for simulation calculation (30) .…”

Section: Discussionmentioning

confidence: 99%

Influence of internal fixation systems on radiation therapy for spinal tumor

Yan

Wang

et al. 2015

J Applied Clin Med Phys

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In this study, the influence of internal fixation systems on radiation therapy for spinal tumor was investigated in order to derive a theoretical basis for adjustment of radiation dose for patients with spinal tumor and internal fixation. Based on a common method of internal fixation after resection of spinal tumor, different models of spinal internal fixation were constructed using the lumbar vertebra of fresh domestic pigs and titanium alloy as the internal fixation system. Variations in radiation dose in the vertebral body and partial spinal cord in different types of internal fixation were studied under the same radiation condition (6 MV and 600 mGy) in different fixation models and compared with those irradiated based on the treatment planning system (TPS). Our results showed that spinal internal fixation materials have great impact on the radiation dose absorbed by spinal tumors. Under the same radiation condition, the influence of anterior internal fixation material or combined anterior and posterior approach on radiation dose at the anterior border of the vertebral body was the greatest. Regardless of the kinds of internal fixation method employed, radiation dose at the anterior border of the vertebral body was significantly different from that at other positions. Notably, the influence of posterior internal fixation material on the anterior wall of the vertebral canal was the greatest. X‐ray attenuation and scattering should be taken into consideration for most patients with bone metastasis that receive fixation of metal implants. Further evaluation should then be conducted with modified TPS in order to minimize the potentially harmful effects of inappropriate radiation dose.PACS number: 87.55.D‐

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“…Wadi-Ramahi et al, suggested that a uniform longitudinal magnetic field of 0.5 T strength could be used to reduce secondary electron out-scatter caused by the presence of an air gap to improve the dose at the distal surface of air cavities. [34]…”

Section: Introductionmentioning

confidence: 99%

Dosimetry of interface region near closed air cavities for Co-60, 6 MV and 15 MV photon beams using Monte Carlo simulations

et al. 2010

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Underdosing of treatment targets can occur in radiation therapy due to electronic disequilibrium around air-tissue interfaces when tumors are situated near natural air cavities. These effects have been shown to increase with the beam energy and decrease with the field size. Intensity modulated radiation therapy (IMRT) and tomotherapy techniques employ combinations of multiple small radiation beamlets of varying intensities to deliver highly conformal radiation therapy. The use of small beamlets in these techniques may therefore result in underdosing of treatment target in the air-tissue interfaces region surrounding an air cavity. This work was undertaken to investigate dose reductions near the air-water interfaces of 1×1×1 and 3×3×3 cm3 air cavities, typically encountered in the treatment of head and neck cancer utilizing radiation therapy techniques such as IMRT and tomotherapy using small fields of Co-60, 6 MV and 15 MV photons. Additional investigations were performed for larger photon field sizes encompassing the entire air-cavity, such as encountered in conventional three dimensional conformal radiation therapy (3DCRT) techniques. The EGSnrc/DOSXYZnrc Monte Carlo code was used to calculate the dose reductions (in water) in air-water interface region for single, parallel opposed and four field irradiations with 2×2 cm2 (beamlet), 10×2 cm2 (fan beam), 5×5 and 7×7 cm2 field sizes. The magnitude of dose reduction in water near air-water interface increases with photon energy; decreases with distance from the interface as well as decreases as the number of beams are increased. No dose reductions were observed for large field sizes encompassing the air cavities. The results demonstrate that Co-60 beams may provide significantly smaller interface dose reductions than 6 MV and 15 MV irradiations for small field irradiations such as used in IMRT and tomotherapy.

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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

Cited by 15 publications

References 13 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.

Influence of internal fixation systems on radiation therapy for spinal tumor

Dosimetry of interface region near closed air cavities for Co-60, 6 MV and 15 MV photon beams using Monte Carlo simulations

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