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Skin dose investigations on a 0.5 T parallel rotating biplanar linac‐MR using Monte Carlo simulations and measurements.

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Title: Skin dose investigations on a 0.5 T parallel rotating biplanar linac‐MR using Monte Carlo simulations and measurements.
Authors: Oliver, Patricia A. K.1,2,3 (AUTHOR) patty.oliver@dal.ca, Yip, Eugene1,2 (AUTHOR), Tari, Shima Y.1,2 (AUTHOR), Wachowicz, Keith1,2 (AUTHOR), Reynolds, Michael1 (AUTHOR), Burke, Ben1,2 (AUTHOR), Warkentin, Brad1,2 (AUTHOR), Fallone, B. Gino1,2,4 (AUTHOR)
Source: Medical Physics. Sep2024, Vol. 51 Issue 9, p6317-6331. 15p.
Subjects: Magnetic field effects, Ionization chambers, Magnetic fields, Ion plating, Magnetic particles, Photon beams
Abstract: Background: The Alberta rotating biplanar linac‐MR has a 0.5 T magnetic field parallel to the beamline. When developing a new linac‐MR system, interactions of charged particles with the magnetic field necessitate careful consideration of skin dose and tissue interface effects. Purpose: To investigate the effect of the magnetic field on skin dose using measurements and Monte Carlo (MC) simulations. Methods: We develop an MC model of our linac‐MR, which we validate by comparison with ion chamber measurements in a water tank. Additionally, MC simulation results are compared with radiochromic film surface dose measurements on solid water. Variations in surface dose as a function of field size are measured using a parallel plate ion chamber in solid water. Using an anthropomorphic computational phantom with a 2 mm‐thick skin layer, we investigate dose distributions resulting from three beam arrangements. Magnetic field on and off scenarios are considered for all measurements and simulations. Results: For a 20 × 20 cm2 field size, D0.2cc${D_{0.2cc}}$ (the minimum dose to the hottest contiguous 0.2 cc volume) for the top 2 mm of a simple water phantom is 72% when the magnetic field is on, compared to 34% with magnetic field off (values are normalized to the central axis dose maximum). Parallel plate ion chamber measurements demonstrate that the relative increase in surface dose due to the magnetic field decreases with increasing field size. For the anthropomorphic phantom, D∼0.2cc${D_{ \sim 0.2cc}}$ (minimum skin dose in the hottest 1 × 1 × 1 cm3 cube) shows relative increases of 20%–28% when the magnetic field is on compared to when it is off. With magnetic field off, skin D∼0.2cc${D_{ \sim 0.2cc}}$ is 71%, 56%, and 21% for medial‐lateral tangents, anterior‐posterior beams, and a five‐field arrangement, respectively. For magnetic field on, the corresponding skin D∼0.2cc${D_{ \sim 0.2cc}}$ values are 91%, 67%, and 25%. Conclusions: Using a validated MC model of our linac‐MR, surface doses are calculated in various scenarios. MC‐calculated skin dose varies depending on field sizes, obliquity, and the number of beams. In general, the parallel linac‐MR arrangement results in skin dose enhancement due to charged particles spiraling along magnetic field lines, which impedes lateral motion away from the central axis. Nonetheless, considering the results presented herein, treatment plans can be designed to minimize skin dose by, for example, avoiding oblique beams and using a larger number of fields. [ABSTRACT FROM AUTHOR]
Copyright of Medical Physics is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
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  Data: Skin dose investigations on a 0.5 T parallel rotating biplanar linac‐MR using Monte Carlo simulations and measurements.
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  Data: <searchLink fieldCode="AR" term="%22Oliver%2C+Patricia+A%2E+K%2E%22">Oliver, Patricia A. K.</searchLink><relatesTo>1,2,3</relatesTo> (AUTHOR)<i> patty.oliver@dal.ca</i><br /><searchLink fieldCode="AR" term="%22Yip%2C+Eugene%22">Yip, Eugene</searchLink><relatesTo>1,2</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Tari%2C+Shima+Y%2E%22">Tari, Shima Y.</searchLink><relatesTo>1,2</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Wachowicz%2C+Keith%22">Wachowicz, Keith</searchLink><relatesTo>1,2</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Reynolds%2C+Michael%22">Reynolds, Michael</searchLink><relatesTo>1</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Burke%2C+Ben%22">Burke, Ben</searchLink><relatesTo>1,2</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Warkentin%2C+Brad%22">Warkentin, Brad</searchLink><relatesTo>1,2</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Fallone%2C+B%2E+Gino%22">Fallone, B. Gino</searchLink><relatesTo>1,2,4</relatesTo> (AUTHOR)
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  Data: <searchLink fieldCode="JN" term="%22Medical+Physics%22">Medical Physics</searchLink>. Sep2024, Vol. 51 Issue 9, p6317-6331. 15p.
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  Data: <searchLink fieldCode="DE" term="%22Magnetic+field+effects%22">Magnetic field effects</searchLink><br /><searchLink fieldCode="DE" term="%22Ionization+chambers%22">Ionization chambers</searchLink><br /><searchLink fieldCode="DE" term="%22Magnetic+fields%22">Magnetic fields</searchLink><br /><searchLink fieldCode="DE" term="%22Ion+plating%22">Ion plating</searchLink><br /><searchLink fieldCode="DE" term="%22Magnetic+particles%22">Magnetic particles</searchLink><br /><searchLink fieldCode="DE" term="%22Photon+beams%22">Photon beams</searchLink>
– Name: Abstract
  Label: Abstract
  Group: Ab
  Data: Background: The Alberta rotating biplanar linac‐MR has a 0.5 T magnetic field parallel to the beamline. When developing a new linac‐MR system, interactions of charged particles with the magnetic field necessitate careful consideration of skin dose and tissue interface effects. Purpose: To investigate the effect of the magnetic field on skin dose using measurements and Monte Carlo (MC) simulations. Methods: We develop an MC model of our linac‐MR, which we validate by comparison with ion chamber measurements in a water tank. Additionally, MC simulation results are compared with radiochromic film surface dose measurements on solid water. Variations in surface dose as a function of field size are measured using a parallel plate ion chamber in solid water. Using an anthropomorphic computational phantom with a 2 mm‐thick skin layer, we investigate dose distributions resulting from three beam arrangements. Magnetic field on and off scenarios are considered for all measurements and simulations. Results: For a 20 × 20 cm2 field size, D0.2cc${D_{0.2cc}}$ (the minimum dose to the hottest contiguous 0.2 cc volume) for the top 2 mm of a simple water phantom is 72% when the magnetic field is on, compared to 34% with magnetic field off (values are normalized to the central axis dose maximum). Parallel plate ion chamber measurements demonstrate that the relative increase in surface dose due to the magnetic field decreases with increasing field size. For the anthropomorphic phantom, D∼0.2cc${D_{ \sim 0.2cc}}$ (minimum skin dose in the hottest 1 × 1 × 1 cm3 cube) shows relative increases of 20%–28% when the magnetic field is on compared to when it is off. With magnetic field off, skin D∼0.2cc${D_{ \sim 0.2cc}}$ is 71%, 56%, and 21% for medial‐lateral tangents, anterior‐posterior beams, and a five‐field arrangement, respectively. For magnetic field on, the corresponding skin D∼0.2cc${D_{ \sim 0.2cc}}$ values are 91%, 67%, and 25%. Conclusions: Using a validated MC model of our linac‐MR, surface doses are calculated in various scenarios. MC‐calculated skin dose varies depending on field sizes, obliquity, and the number of beams. In general, the parallel linac‐MR arrangement results in skin dose enhancement due to charged particles spiraling along magnetic field lines, which impedes lateral motion away from the central axis. Nonetheless, considering the results presented herein, treatment plans can be designed to minimize skin dose by, for example, avoiding oblique beams and using a larger number of fields. [ABSTRACT FROM AUTHOR]
– Name: AbstractSuppliedCopyright
  Label:
  Group: Ab
  Data: <i>Copyright of Medical Physics is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.)
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        Value: 10.1002/mp.17246
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      – Code: eng
        Text: English
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        PageCount: 15
        StartPage: 6317
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      – SubjectFull: Magnetic field effects
        Type: general
      – SubjectFull: Ionization chambers
        Type: general
      – SubjectFull: Magnetic fields
        Type: general
      – SubjectFull: Ion plating
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      – SubjectFull: Photon beams
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      – TitleFull: Skin dose investigations on a 0.5 T parallel rotating biplanar linac‐MR using Monte Carlo simulations and measurements.
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              M: 09
              Text: Sep2024
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              Y: 2024
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