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Release of Patients Administered Radioactive Materials

Procedures for Calculating Doses Based on Patient-Specific Factors

Based on NRC Regulatory Guide 8.39

RegGuide 8.39 (revised April 1997)


This web form calculates the potential dose to other individuals based on Appendix B of RegGuide 8.39.
D(t) = Accumulated dose to time t, in rems
34.6 = Conversion factor of 24 hrs/day times the total integration of decay (1.44)
Γ = Exposure rate constant for a point source, R/mCi x hr at 1 cm
Qo = Initial activity at the start of the time interval
Tp = Physical half-life in days
r² = Distance in centimeters - typically 100 cm
E1 = Occupancy factor for the first 8 hours
E2 = Occupancy factor from 8 hours to total decay
F1 = Extrathyroidal uptake fraction
F2 = Thyroidal uptake fraction


Equation B-1



Equation B-5


For I-131 patients there are three factors that must be determined:

  1. Initial Activity (in millicuries)
  2. Medical Condition
  3. Occupancy Factor from 8 hours to total decay

Initial Acitivity (in millicuries):

Which of the following Medical Conditions applies to the patient?
Hyperthyroidism.
Postthyroidectomy for thyroid cancer.
None of the above.

Which of the following Occupancy Factors applies to the patient during the period from 8 hours after administration until total decay?
E = 0.75 - When a physical half-life, an effective half-life, or a specific time period under consideration (e.g., bladder holding time) is less than or equal to 1 day.

E = 0.25 - When an effective half-life is greater than 1 day if the patient has been given instructions, such as,
Maintain a prudent distance from others for at least the first two days,
Sleep alone in a room for at least the first night,
Do not travel by airplane or mass transportation for at least the first day,
Do not travel on a prolonged automobile trip with others for at least the first two days,
Have sole use of a bathroom for at least the first two days,
Drink plenty of fluids for at least the first two days.

E = 0.125 - When an effective half-life is greater than 1 day if the patient has been given instructions, such as,
Follow the instructions for E = 0.25 above,
Live alone for at least the first two days,
Have few visits by family or friends for at least the first two days.