I-131 Patient Release Dose Calculation Principles & Recent Research Lynn McGuire, MS, DABMP Consultant Medical Physicist (ret) UAMS Department of Radiology

Dose to others from an I-131 patient Dose calculation methods & fundamentals Physical principles, geometry and scenarios More realistic geometries per Young, et al publications

Dose calculation methods & fundamentals Source – Target Physical - T 1/2, decay scheme Geometry Scenarios –Time & distance –Phantoms Biology – kinetics, time course of activity

Isotope physical data T 1/2, decay scheme I-131: 8 da, 364 keV gamma, 80% emission. =.22 1m

Geometries Target Point 3D Source Point 2D – Line 3D (distributed, volume)

Point source geometry

Geometries Target Point 3D Source Point 2D – Line 3D (distributed, volume) Phantoms & patients –Gender –Age –Posture –Activity distribution Disease state

Dosimetry phantoms - early

ORNL stylized

UF/NCI

Exposure Scenarios –Time = Occ. Factor (OF or E) –distance –Phantoms

Exposure Scenarios –Time & distance –Phantoms

I-131 distribution

NOW we can do those pesky dose calcs…

Dosimetry First Principles Physical decay Physical + biological D(∞)= 34.6*D 0 *T p (34.6=24*1.44) D(∞)= 34.6*D 0 *T E (T E =Tp*Tb/(Tp+Tb)

Dosimetry First Principles (2) Physical + biological w/occup factor E NRC case, App U-2 D(∞)= 34.6*D 0 *T E *E D= 34.6*.22*33mCi*8da*1/4=500 mrem

Physical decay only, with E (occ factor) 34.6

Time-activity or Retention curve

MIRD dosimetry Teff

NUREG 1556 App U, eq B-5

Regulatory reqt.

NUREG-1556 assumes point target, source

Han et al publications

All pubs posted at elmmhp.wordpress.com

Han, et al publications PhD research UF UF/NCI phantom family MCNP code code for photon transport Dose as TEDE Develop s-factors for multiple scenarios Use NRC uptake& retention model Provides mSv/ (mR/h) values Suggested time restrictions

Han exposure scenarios Phantom – age/gender Orientation – Facing; side to side; holding (infants) Hyperthyroidism & cancer – activity distribution

(MCNP) Monte carlo

RPD paper

MP paper: S-factors, hyper & organ doses

8x-80x greater 2x-20x greater

Fraction of adult TEDE Tables 2 & 3, Han et al, JRP cm 100 cm 200 cm HyperDTCHyperDTCHyperDTC 1 yo.11E-21.8E-26.7E-210E-212E-2 5 yo7E-254E-279E-298E-2100E-2

Takeaways NRC point source method conservative Han et al -<1/2 NRC, implies thy ca discharge OK ~400 mCi -S-factors given for non standard or default cases -Dose with age -Distance: dose similar to point sources >1 m, <1 m

Future refinements? REAL patient specific data – Biodistribution – SPECT/PET/CT Useful for more precise patient treatment/dose Necessary for patient release?