Technical Note: Response measurement for select radiation detectors in magnetic fields

Reynolds, M; Fallone, B. G.; Rathee, S

doi:10.1118/1.4919681

Cited by 21 publications

(19 citation statements)

References 15 publications

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“…In addition to the consequences of the magnetic field on dose distributions, the question of calibration and dosimetry in magnetic fields has arisen. [12][13][14] Ion chamber and solid state detector responses per unit dose are found to vary by several percent in the presence of a magnetic field when compared to the 0 T case. [14][15][16] This necessitates the calculation of high precision correction factors, and reliable and accurate Monte Carlo techniques to handle the magnetic fields.…”

Section: Introductionmentioning

confidence: 99%

Charged particle transport in magnetic fields in EGSnrc

2016

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Section: Introductionmentioning

confidence: 99%

Charged particle transport in magnetic fields in EGSnrc

2016

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“…There has been focus in the literature on reference dosimetry in magnetic fields, particularly correction factors for ionization chambers. [17][18][19][20][21][22][23] Some groups have investigated the response of point diodes, 24 diode arrays, 25 and diamond detectors 24,26 in fields of both orientations and varying strengths. More recently, there have been studies on the effects on relative dosimetry.…”

Section: Introductionmentioning

confidence: 99%

Experimental characterization of magnetically focused electron contamination at the surface of a high‐field inline MRI‐linac

Roberts¹,

Patterson

Jelen

et al. 2019

Medical Physics

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Purpose The fringe field of the Australian MRI‐linac causes contaminant electrons to be focused along the central axis resulting in a high surface dose. This work aims to characterize this effect using Gafchromic film and high‐resolution detectors, MOSkinTM and microDiamond. The secondary aim is to investigate the influence of the inline magnetic field on the relative dose response of these detectors. Methods The Australian MRI‐linac has the unique feature that the linac is mounted on rails allowing for measurements to be performed at different magnetic field strengths while maintaining a constant source‐to‐surface distance (SSD). Percentage depth doses (PDD) were collected at SSD 1.82 m in a solid water phantom positioned in a low magnetic field region and then at isocenter of the MRI where the magnetic field is 1 T. Measurements for a range of field sizes were taken with the MOSkinTM, microDiamond, and Gafchromic® EBT3 film. The detectors’ relative responses at 1 T were compared to the near 0 T PDD beyond the region of electron contamination, that is, 20 mm depth. The near surface measurements inside the MRI bore were compared among the different detectors. Results Skin dose in the MRI, as measured with the MOSkinTM, was 104.5% for 2.1 × 1.9 cm2, 185.6% for 6.1 × 5.8 cm2, 369.1% for 11.8 × 11.5 cm2, and 711.1% for 23.5 × 23 cm2. The detector measurements beyond the electron contamination region showed agreement between the relative response at 1 T and near 0 T. Film was in agreement with both detectors in this region further demonstrating their relative response is unaffected by the magnetic field. Conclusions Experimental characterization of the high electron contamination at the surface was performed for a range of field sizes. The relative response of MOSkinTM and microDiamond detectors, beyond the electron contamination region, were confirmed to be unaffected by the 1‐T inline magnetic field.

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“…This magnetic field disrupts the deposition of dose (in a patient or a phantom) by deflecting the paths of the secondary electrons via the Lorentz force . In addition, the dose–response of the detectors used to characterize and calibrate the beam is also affected …”

Section: Introductionmentioning

confidence: 99%

“…Most of the work done so far to characterize the behavior of detectors in a magnetic field has focused on the effect of the magnetic field on the absolute dose–response of the detector as a function of magnetic field strength and detector orientation under certain conditions. Significant changes to the dose–response of both ionization chambers and solid‐state detectors have been observed. However, the effect of the magnetic field on relative dosimetry measurements is unclear.…”

Section: Introductionmentioning

confidence: 99%

“…[6][7][8][9][10][11] In addition, the dose-response of the detectors used to characterize and calibrate the beam is also affected. [11][12][13][14][15][16][17][18][19] Most of the work done so far to characterize the behavior of detectors in a magnetic field has focused on the effect of the magnetic field on the absolute dose-response of the detector as a function of magnetic field strength and detector orientation under certain conditions. Significant changes to the dose-response of both ionization chambers [11][12][13][14][15][16] and solid-state detectors [17][18][19] have been observed.…”

Section: Introductionmentioning

confidence: 99%

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Relative dosimetry with an MR‐linac: Response of ion chambers, diamond, and diode detectors for off‐axis, depth dose, and output factor measurements

et al. 2017

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The magnetic field of the MR-linac alters the effective point of measurement of ionization chambers, shifting it both downstream and laterally. Shielded diodes produce incorrect and misleading dose profiles. The output factor measured at the point of peak intensity in the lateral dose distribution is more robust than the conventional output factor (measured at central axis). Diodes are not recommended for output factor measurements in the magnetic field.

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Technical Note: Response measurement for select radiation detectors in magnetic fields

Abstract: Low field longitudinal magnetic fields have been shown to have little or no effect on the dose response of the detectors investigated and further lend credibility to previous simulation only studies.

Cited by 21 publications

References 15 publications

Charged particle transport in magnetic fields in EGSnrc

Charged particle transport in magnetic fields in EGSnrc

Experimental characterization of magnetically focused electron contamination at the surface of a high‐field inline MRI‐linac

Relative dosimetry with an MR‐linac: Response of ion chambers, diamond, and diode detectors for off‐axis, depth dose, and output factor measurements

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