Technical Note: Dose effects of 1.5 T transverse magnetic field on tissue interfaces in MRI-guided radiotherapy

Chen, Xinfeng; Prior, Phillip; Chen, Guang‐Pei; Schultz, Christopher J.; Li, X. Allen

doi:10.1118/1.4959534

Cited by 52 publications

(54 citation statements)

References 16 publications

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“…The dosimetric effect of a transverse magnetic field (TMF) in phantom and patients has been studied extensively . Compared to conventional external beam RT without magnetic field, the magnetic field can generally lead to an altered buildup depth, and a larger, slightly shifted (asymmetric) penumbra arising from tilting of the dose kernel .…”

Section: Introductionmentioning

confidence: 99%

Measurement validation of treatment planning for a MR‐Linac

Chen

Paulson

Ahunbay

et al. 2019

J Applied Clin Med Phys

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Purpose The magnetic field can cause a nonnegligible dosimetric effect in an MR‐Linac system. This effect should be accurately accounted for by the beam models in treatment planning systems (TPS). The purpose of the study was to verify the beam model and the entire treatment planning and delivery process for a 1.5 T MR‐Linac based on comprehensive dosimetric measurements and end‐to‐end tests. Material and methods Dosimetry measurements and end‐to‐end tests were performed on a preclinical MR‐Linac (Elekta AB) using a multitude of detectors and were compared to the corresponding beam model calculations from the TPS for the MR‐Linac. Measurement devices included ion chambers (IC), diamond detector, radiochromic film, and MR‐compatible ion chamber array and diode array. The dose in inhomogeneous phantom was also verified. The end‐to‐end tests include the generation, delivery, and comparison of 3D and IMRT plan with measurement. Results For the depth dose measurements with Farmer IC, micro IC and diamond detector, the absolute difference between most measurement points and beam model calculation beyond the buildup region were <1%, at most 2% for a few measurement points. For the beam profile measurements, the absolute differences were no more than 1% outside the penumbra region and no more than 2.5% inside the penumbra region. Results of end‐to‐end tests demonstrated that three 3D static plans with single 5 × 10 cm2 fields (at gantry angle 0°, 90° and 270°) and two IMRT plans successfully passed gamma analysis with clinical criteria. The dose difference in the inhomogeneous phantom between the calculation and measurement was within 1.0%. Conclusions Both relative and absolute dosimetry measurements agreed well with the TPS calculation, indicating that the beam model for MR‐Linac properly accounts for the magnetic field effect. The end‐to‐end tests verified the entire treatment planning process.

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Section: Introductionmentioning

confidence: 99%

Measurement validation of treatment planning for a MR‐Linac

Chen

Paulson

Ahunbay

et al. 2019

J Applied Clin Med Phys

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“…The effect of the magnetic field during MRgRT on the dose deposition has been shown to be influenced by the magnetic field strength, the incident beam energy, the beam entrance angle, and the boundary shape . Studies show that clinically acceptable plans can be achieved with multiple beam configurations over the target, and it has even been suggested that dosimetric effects due to the magnetic field could be used to develop partial breast MRgRT treatments …”

Section: Introductionmentioning

confidence: 99%

“…5,6 The effect of the magnetic field during MRgRT on the dose deposition has been shown to be influenced by the magnetic field strength, the incident beam energy, the beam entrance angle, and the boundary shape. [7][8][9][10] Studies show that clinically acceptable plans can be achieved with multiple beam configurations over the target, [10][11][12] and it has even been suggested that dosimetric effects due to the magnetic field could be used to develop partial breast MRgRT treatments. 13 However, as typical MRgRT workflows include daily imaging and a certain degree of adaptation of the original plan, the patient can be lying on the treatment coach for up to 30 min before treatment delivery.…”

Section: Introductionmentioning

confidence: 99%

Assessing localized dosimetric effects due to unplanned gas cavities during pelvic MR‐guided radiotherapy using Monte Carlo simulations

et al. 2019

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Purpose It has been proposed that beam modulation and opposing beam configurations can cancel effects of the Electron Return Effect (ERE) during MR‐guided radiotherapy (MRgRT). However, this may not always be the case for unplanned gas cavities outside of the target in the pelvic region. We evaluate dosimetric effects, including effects in the rectal wall, due to unplanned spherical air cavities during MRgRT. Methods Nine virtual cuboid water phantoms containing spherical air cavities (0.5–7.5 cm diameter) and a reference phantom without air were created. Monte Carlo dose calculations of 7 MV photons under the influence of a 1.5 T transverse magnetic field were produced using Monaco 5.19.02 Treatment Planning System (TPS) (Elekta AB, Stockholm, Sweden). Cavities in the path of a single and multiple beam plans were considered. Dose distributions of phantoms with and without air cavities were compared (ΔD%) using a spherical coordinate system originating in the center of the cavity. Effects in the rectal wall were quantified by comparing dose volume histogram (DVH) parameters for solid and gaseous filling from simulated rectal wall structures. Results Max(ΔD%) of ~70% and 20% were observed around large cavities in the path of a single and multiple beam plans, respectively. Approximately 45 cm3 of phantom surrounding the largest cavity in a single beam received dose changes of >10%. Dmean in the rectal wall was unchanged when comparing gaseous and solid filling in the path of a single beam; however, D1cc and Dmax increased by up to ~45% and ~63%, respectively. Conclusions Unplanned gas cavities in the path of a single beam during pelvic MRgRT with a 1.5 T transverse magnetic field cause dose changes which may impact toxicity in the rectal wall, depending on local dose and fractionation. Effects are reduced but not eliminated with a five‐beam plan.

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“…Raaijmakers et al [2] [3] demonstrated the ERE by MC simulation, which was also validated by film measurement in sold water phantoms. Chen et al investigated the dosimetric effect of ERE at air-tissue and lung-tissue interfaces during intensity modulated radiation therapy (IMRT) [5]. Woodings et al conducted a comprehensive dosimetric characterization of the Elekta 1.5T MR-Linac beam for clinical application [6].…”

Section: Introductionmentioning

confidence: 99%

Measurement of Electron Return Effect and Skin Dose Reduction by a Bolus in an Anthropomorphic Physical Phantom under a Magnetic Resonance Guided Linear Accelerator (MR-LINAC) System

Han¹,

Wen²,

Lee³

et al. 2018

IJMPCERO

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Background: Magnetic resonance image-guided radiation therapy (MR-IGRT) promises more precise and effective radiation treatments compared to conventional IGRT by using real-time on-board MR imaging. Under the influence of a magnetic field, however, secondary electrons exiting a surface can be forced in a circular path and re-enter the medium, resulting in dose increase at a beam-exit surface, called the electron return effect (ERE). The purpose of the study is to compare the exit skin dose computed by Monte Carlo dose calculation with measurements using an adult anthropomorphic phantom and to measure the effect of skin dose reduction by adding 1 cm-thick bolus. Method: The plan was compared with measurements using an adult anthropomorphic phantom combined with radiochromic films and thermoluminescent dosimeters. We also measured the skin dose reduction by adding 1 cm-thick bolus on the frontal surface of the phantom. Results: We found that 1 cm-thick bolus reduced the skin dose by up to 20% both in measurements and calculations. The plan was found to overestimate the measured skin dose by about 10% and there was no significant difference in the bolus effect between the breast skin and the skin (without breast attachment) doses. Conclusion: In conclusion, we confirmed the ERE effect on the anthropomorphic phantom under the magnetic field and the exit skin dose reduction by adding a bolus. Skin dose measurements using anthropomorphic phantom may be helpful to evaluate more realistic skin dose and the bo-How to cite this paper:

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Technical Note: Dose effects of 1.5 T transverse magnetic field on tissue interfaces in MRI-guided radiotherapy

Cited by 52 publications

References 16 publications

Measurement validation of treatment planning for a MR‐Linac

Measurement validation of treatment planning for a MR‐Linac

Assessing localized dosimetric effects due to unplanned gas cavities during pelvic MR‐guided radiotherapy using Monte Carlo simulations

Measurement of Electron Return Effect and Skin Dose Reduction by a Bolus in an Anthropomorphic Physical Phantom under a Magnetic Resonance Guided Linear Accelerator (MR-LINAC) System

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