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Out of field doses

Doses measured out of field for SCE, ESE and HLS. Data collected using film and OSLDs. In house phantoms, solid water and the anterior imaging coil were irradiated and out of field doses were recorded. 

[Abstract: Related publication]: With the clinical introduction of MR-linacs, out-of-field dose (OFD) associated with head leakage/scatter (HLS), spiralling contaminant electrons (SCE) and the electron streaming effect (ESE) is of interest. To investigate HLS and SCE, EBT3 film on solid water 5.0 cm beyond each edge of a 10.0 × 10.0 cm2 field was used to determine depth-dose for 0 T and 1.5 T, in the isocentric plane. Additionally, ESE induced by the anterior imaging coil was quantified and the experimental arrangements to measure SCE and ESE were modelled using Monaco. For a clinical treatment of supraclavicular nodal disease, Monaco OFD was compared to in vivo measurements. For 0 T, depth-dose was isotropic and surface dose was approximately 4.4% of Dmax. With 1.5 T surface doses were approximately 3.8% of Dmax at ± Y (IEC61217), compared to 2.6% and 0.6% of Dmax at − X and X, respectively. For both field strengths, the TPS depth-dose variation was consistent with experimental trends; however, near surface doses calculated at ± Y differed significantly from measurements. For the field sizes investigated, measured coil ESE dose was between 9.0 and 28.0% of Dmax and Monaco coil ESE was less than measured by up to 13.0%. OFD in 0 T and 1.5 T are comparable at ± Y, inconsistent with previous work. Anterior coil ESE should be mitigated during treatment and for the clinical case investigated, in vivo OFD was within 2σ of TPS calculations. Monaco overestimates near surface SCE and underestimates coil ESE.

Software/equipment used to create/collect the data: Software:
Verisoft v7.2 (PTW, Freiburg, Germany)
FilmQA Pro v5.0 (Ashland ISP Advanced Materials, NJ, USA)
ImageJ v1.53a (NIH, Bethesda, MD, USA) 

Equipment:
Octavius 1500MR array (PTW, Freiburg Germany)
PTW 30013 Farmer Ionisation chambers (PTW, Freiburg, Germany)
RW3 Solid water (PTW, Freiburg, Germany)
Solid Water® HE (Gammex Inc – A Sun Nuclear Company, Middleton, WI, USA)
Gafchromic EBT3/XD/RTQA film (Ashland ISP Advanced Materials, NJ, USA)
OSLDs (LANDAUER®, Glenwood, IL, USA)
microSTAR®ii Dosimetry Reader (LANDAUER®, Glenwood, IL, USA)

Software/equipment used to manipulate/analyse the data: Excel
MATLAB® 2018a (MathWorks, Natick, MA, USA)
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    Data Record Details
    Data record related to this publication Out of Field Doses
    Data Publication title Out of field doses
  • Description

    Doses measured out of field for SCE, ESE and HLS. Data collected using film and OSLDs. In house phantoms, solid water and the anterior imaging coil were irradiated and out of field doses were recorded. 

    [Abstract: Related publication]: With the clinical introduction of MR-linacs, out-of-field dose (OFD) associated with head leakage/scatter (HLS), spiralling contaminant electrons (SCE) and the electron streaming effect (ESE) is of interest. To investigate HLS and SCE, EBT3 film on solid water 5.0 cm beyond each edge of a 10.0 × 10.0 cm2 field was used to determine depth-dose for 0 T and 1.5 T, in the isocentric plane. Additionally, ESE induced by the anterior imaging coil was quantified and the experimental arrangements to measure SCE and ESE were modelled using Monaco. For a clinical treatment of supraclavicular nodal disease, Monaco OFD was compared to in vivo measurements. For 0 T, depth-dose was isotropic and surface dose was approximately 4.4% of Dmax. With 1.5 T surface doses were approximately 3.8% of Dmax at ± Y (IEC61217), compared to 2.6% and 0.6% of Dmax at − X and X, respectively. For both field strengths, the TPS depth-dose variation was consistent with experimental trends; however, near surface doses calculated at ± Y differed significantly from measurements. For the field sizes investigated, measured coil ESE dose was between 9.0 and 28.0% of Dmax and Monaco coil ESE was less than measured by up to 13.0%. OFD in 0 T and 1.5 T are comparable at ± Y, inconsistent with previous work. Anterior coil ESE should be mitigated during treatment and for the clinical case investigated, in vivo OFD was within 2σ of TPS calculations. Monaco overestimates near surface SCE and underestimates coil ESE.

    Software/equipment used to create/collect the data: Software:
    Verisoft v7.2 (PTW, Freiburg, Germany)
    FilmQA Pro v5.0 (Ashland ISP Advanced Materials, NJ, USA)
    ImageJ v1.53a (NIH, Bethesda, MD, USA) 

    Equipment:
    Octavius 1500MR array (PTW, Freiburg Germany)
    PTW 30013 Farmer Ionisation chambers (PTW, Freiburg, Germany)
    RW3 Solid water (PTW, Freiburg, Germany)
    Solid Water® HE (Gammex Inc – A Sun Nuclear Company, Middleton, WI, USA)
    Gafchromic EBT3/XD/RTQA film (Ashland ISP Advanced Materials, NJ, USA)
    OSLDs (LANDAUER®, Glenwood, IL, USA)
    microSTAR®ii Dosimetry Reader (LANDAUER®, Glenwood, IL, USA)

    Software/equipment used to manipulate/analyse the data: Excel
    MATLAB® 2018a (MathWorks, Natick, MA, USA)

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  • Other Descriptors
    • Descriptor
      Out of field doses measured on an Elekta Unity MRL. Data contained in spreadsheets. Dose from SCE, ESE and HLS investigated and recorded.
      • Descriptor type Brief
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  • Keywords
    • medicalphysics
    • Elekta Unity
    • MR-Linac
    • Lorentz Force
    • MRgRT
    • Out-of-field dose
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- Citation
    Citation Powers, Marcus; White, Ronald (2022): Out of field doses. James Cook University. https://doi.org/10.25903/snzx-c059