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Title: SU-E-J-38: Comparison of 6MV Photon Dose in a Perpendicular and Parallel Magnetic Field

Abstract

Purpose: Integrating a linac with an MRI system would allow for real time tumour tracking however the patient will be irradiated in the presence of a magnetic field. The present study experimentally investigates the magnetic field effects on entrance, exit, and interface dose for both transverse and parallel magnetic fields. Methods: Polystyrene was used to construct a set of phantoms for Gafchromic film measurements. One phantom had an adjustable air gap and four other phantoms had one surface at various angles. The linac-MR prototype consisting of a biplanar permanent magnet coupled to a linac was used for the transverse magnetic field measurements. A couple of solenoid electromagnets, stacked on top of each other and irradiated along their bore, were used for the parallel field measurements. Results: All doses are relative to no magnetic field. The transverse magnetic field reduced the entrance dose for all surface angles by strongly deflecting the contaminant electrons. The exit dose in a transverse magnetic field was found to be significantly higher. The entrance dose with a parallel magnetic field present is higher due to the contaminant electrons being concentrated within the beam area. The air gap phantom measurements, done in a transverse magnetic field, showmore » a significant increase of the dose at the proximal side of the air gap and a decrease at the distal side. The measurements, done in the parallel magnetic field, show the concentration of secondary electrons in the air gap. Conclusion: The radiation dose measurements of a 6MV beam in a parallel and transverse magnetic field presented here are currently being replicated using Monte Carlo simulations. This verified Monte Carlo system could provide the dose calculation basis for future linac-MR systems.« less

Authors:
; ;  [1]
  1. Cross Cancer Institute, Edmonton, AB (Canada)
Publication Date:
OSTI Identifier:
22325300
Resource Type:
Journal Article
Journal Name:
Medical Physics
Additional Journal Information:
Journal Volume: 41; Journal Issue: 6; Other Information: (c) 2014 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0094-2405
Country of Publication:
United States
Language:
English
Subject:
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; 60 APPLIED LIFE SCIENCES; AIR; COMPUTERIZED SIMULATION; CONCENTRATION RATIO; ELECTRONS; LINEAR ACCELERATORS; MAGNETIC FIELDS; MONTE CARLO METHOD; NMR IMAGING; PHANTOMS; PHOTONS; POLYSTYRENE; RADIATION DOSES; SOLENOIDS

Citation Formats

Ghila, A, Fallone, B, and Rathee, S. SU-E-J-38: Comparison of 6MV Photon Dose in a Perpendicular and Parallel Magnetic Field. United States: N. p., 2014. Web. doi:10.1118/1.4888090.
Ghila, A, Fallone, B, & Rathee, S. SU-E-J-38: Comparison of 6MV Photon Dose in a Perpendicular and Parallel Magnetic Field. United States. https://doi.org/10.1118/1.4888090
Ghila, A, Fallone, B, and Rathee, S. 2014. "SU-E-J-38: Comparison of 6MV Photon Dose in a Perpendicular and Parallel Magnetic Field". United States. https://doi.org/10.1118/1.4888090.
@article{osti_22325300,
title = {SU-E-J-38: Comparison of 6MV Photon Dose in a Perpendicular and Parallel Magnetic Field},
author = {Ghila, A and Fallone, B and Rathee, S},
abstractNote = {Purpose: Integrating a linac with an MRI system would allow for real time tumour tracking however the patient will be irradiated in the presence of a magnetic field. The present study experimentally investigates the magnetic field effects on entrance, exit, and interface dose for both transverse and parallel magnetic fields. Methods: Polystyrene was used to construct a set of phantoms for Gafchromic film measurements. One phantom had an adjustable air gap and four other phantoms had one surface at various angles. The linac-MR prototype consisting of a biplanar permanent magnet coupled to a linac was used for the transverse magnetic field measurements. A couple of solenoid electromagnets, stacked on top of each other and irradiated along their bore, were used for the parallel field measurements. Results: All doses are relative to no magnetic field. The transverse magnetic field reduced the entrance dose for all surface angles by strongly deflecting the contaminant electrons. The exit dose in a transverse magnetic field was found to be significantly higher. The entrance dose with a parallel magnetic field present is higher due to the contaminant electrons being concentrated within the beam area. The air gap phantom measurements, done in a transverse magnetic field, show a significant increase of the dose at the proximal side of the air gap and a decrease at the distal side. The measurements, done in the parallel magnetic field, show the concentration of secondary electrons in the air gap. Conclusion: The radiation dose measurements of a 6MV beam in a parallel and transverse magnetic field presented here are currently being replicated using Monte Carlo simulations. This verified Monte Carlo system could provide the dose calculation basis for future linac-MR systems.},
doi = {10.1118/1.4888090},
url = {https://www.osti.gov/biblio/22325300}, journal = {Medical Physics},
issn = {0094-2405},
number = 6,
volume = 41,
place = {United States},
year = {Sun Jun 01 00:00:00 EDT 2014},
month = {Sun Jun 01 00:00:00 EDT 2014}
}