Research ArticleRadiation Safety

An Excel-Based System to Manage Radiation Safety for the Family of Patients Undergoing 131I Therapy

Palmer G. Steward
Journal of Nuclear Medicine Technology June 2017, 45 (2) 102-110; DOI: https://doi.org/10.2967/jnmt.116.185322

Article Figures & Data

Figures

  • FIGURE 1.
    FIGURE 1.

    Geometric representation of parallel model. Fraction of administered radionuclide that initially resides in extrathyroidal space and remaining fraction taken up by thyroid are represented by F1 and F2, respectively. Radionuclide in each of these compartments biologically transfers directly into excretion compartment with rate constants λbio1 and λbio2. Although this flow pattern is biologically unrealistic, it provides typical biphasic retention profile, and it has advantage of being mathematically simple. Radionuclide content of extrathyroidal space, modeled as uniformly distributed cylindric volume source, and content of thyroid, modeled as point source, determine radiation field strength in vicinity of patient.

  • FIGURE 2.
    FIGURE 2.

    Biphasic retention function generated by parallel model using parameters that would be suitable for thyrogen-prepared 131I ablation patient. For phase 1 (extrathyroidal space), initial uptake is 97% and effective half-life is 8 h. For phase 2 (thyroid), initial uptake is 3% and effective half-life is 5 d.

  • FIGURE 3.
    FIGURE 3.

    Geometric representation of serial model. Radionuclide in compartment 2 (thyroid) biologically transfers into compartment 1 (extrathyroidal space) and that in compartment 1 transfers to bladder, which then periodically empties into environment. This model is used to estimate radioactive content of each compartment and of periodic urinations as function of time.

  • FIGURE 4.
    FIGURE 4.

    Small section of EXT worksheet of workbook 2. Cells that are unprotected and thus available to user for input have yellow fill. Cells corresponding to forbidden doses have magenta fill, and those with permitted doses are green.

Tables

  • TABLE 1

    Mathematic Notations and Definitions

    NotationDefinition
    B2The transmission factor for radiation emanating from compartment 2 (thyroid)
    d1The distance (m) to a bystander from the patient’s skin at the extrathyroidal source
    d2The distance (m) to a bystander from the patient’s skin at the thyroid
    Δd1The depth in the patient (m) of the extrathyroidal line source
    Δd2The depth in the patient (m) of the thyroidal point source
    Embedded ImageThe fraction of administered isotope initially partitioned into compartment 1
    Embedded ImageThe fraction of administered isotope initially partitioned into compartment 2
    giThe perpendicular distance from the cylinder’s ith line source to the dose point
    ΔgiThe perpendicular distance from the cylinder’s ith line source to the cylinder’s surface in the direction of the dose point
    HVLThe broad-beam half-value layer in water (m) of 131I’s 364-keV photon (the value 0.1 m is used, reference (9))
    Embedded ImageThe air kerma rate at the position of a bystander resulting from patient emanations
    Embedded ImageThe total air kerma at the position of a bystander beginning at a start time ts
    lVariable of integration, distance from midpoint of a line source to line source element dl
    LThe length (m) of the line source
    Embedded ImageThe amount of isotope remaining in metabolic compartment 1 (extrathyroid) at time t
    Embedded ImageThe amount of isotope remaining in metabolic compartment 2 (thyroid) at time t
    Embedded ImageThe amount of isotope in the bladder at time t when the previous urination was at time T
    Embedded ImageThe amount of isotope remaining in the patient at time t (parallel model)
    Embedded ImageThe amount of isotope initially administered
    Embedded ImageThe effective half-life for the radioisotope leaving metabolic compartment 1
    Embedded ImageThe effective half-life for the radioisotope leaving metabolic compartment 2
    TocThe occupancy factor, that is, the average fraction of time that a specific bystander is present at a specified location
    tsThe time that a family member or other bystander begins exposure to the patient’s radiation field
    ΓThe air kerma rate constant (mGy/h/MBq at 1 m) for the radioisotope (the value 5.1613E−5 is used for 131I)
    Embedded ImageThe rate constant for the radioisotope leaving a metabolic compartment by nuclear decay
    Embedded ImageThe rate constant for the isotope leaving metabolic compartment 1 by biologic processes
    Embedded ImageThe rate constant for the isotope leaving metabolic compartment 2 by biologic processes
    Embedded ImageThe effective rate constant for the isotope leaving metabolic compartment 1
    Embedded ImageThe effective rate constant for the isotope leaving metabolic compartment 2
    Embedded ImageThe relationship between rate constant and half-life, where ln(2) is the natural log of 2
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