NPC Patient Release Calculation

Initial Activity:  The dosage administered to the patient (in millicuries)

Uptake Fraction: The fraction of the administered activity that is taken up in the thyroidal tissue. The value is expressed as a decimal. Regulatory Guide 8.39 recommends a value of 0.80 for hyperthyroidism treatments and 0.05 for postthyoroidectomy treatments. The value measured for the specific patient should be entered if available.

Effective Half-life / Thyroidal:   The effective half-life, in days, of I-131 iodide in the thyoridal tissue. The values recommended in Regulatory Guide 8.39 are 5.2 days for hyperthyroidism and 7.3 days for postthyroidectomy cases.

Effective Half-life / Extrathyroidal:   The effective half-life, in days, of I-131 iodide in the body excluding thyroidal tissue. The value recommended in Regulatory Guide 8.39 is 0.32 days.

Occupancy Factor / First Eight Hours:   Regulatory Guide 8.39 recommends an occupancy factor of 0.75 at 1 meter for the first 8 hours. This value is recommended as the effective half-life for the extrathyroidal compartment is less than 1 day.

Occupancy Factor / After Eight Hours:   Regulatory Guide 8.39 recommends an occupancy factor of 0.25 at 1 meter after the first eight hours. This values is recommended as the effective half life for the thyroidal compartment is greater than one day. This factor is based on the assumption that the appropriate instructions are given to and followed by the patient.  Regulatory Guide 8.39 should be referenced for details.

Distance to Patient:  The distance at which the dose to other individuals is calculated. The occupancy factors are defined at this distance. Regulatory Guide 8.39 specifies a distance of 1 meter. (Distance must be entered in cm.)

Last modified: October 23, 2009