Educational Objectives

Releasing Nuclear Medicine
Patients to the Public:
Dose Calculations and Discharge
Instructions
Robert E. Reiman, MD
Radiation Safety Division
Duke University Medical Center
Durham, NC

Medically Useful Iodine Isotopes
IsotopeHalf-life

Primary
Emissions

Use

I-123

13.3 hours γ (0.158 MeV)

Diagnosis

I-124

4.2 daysβ+ and γ (0.511
MeV +)

Diagnosis,
Therapy(?)

I-125

59.4 daysγ (0.035 MeV)

Brachytherapy

I-131

8.0 daysβ- (0.606 MeV),
γ (0.364 MeV)

Diagnosis,
Therapy• Introduce participants to the medical conditions that aretreated with radioiodine.
• Review the regulatory considerations regarding
inpatient and outpatient radioiodine procedures.
• Review ways in which the regulatory requirements may
be satisfied, including “public” radiation dosecomputations, content of post-discharge instructions
and addressing the concerns of patients and theirfamilies.
• Introduce Web-based methods to facilitate
documentation of outpatient treatment.

Treatment of Toxic Goiter• Surgery (not done, except for very large
thyroid, low iodine uptake, cancer orpregnancy)• Drugs (propylthiouracil) and beta blockers(short-term)• Ablation with radioactive iodine

Radioiodine Treatment

Thyroid Carcinoma• I-131 sodium iodide solution, orally• 8 – 15 millicuries for diffuse toxic goiter• 15 – 40 millicuries for toxic multinodulargoiter• Must know the % uptake at 24 hours tocompute administered activity andclearance rates• Incidence: about 3 per 100,000 per year
• Females > Males (2:1)• About 80% papillary type; remainderfollicular or medullary types.
• Medullary thyroid carcinoma does nottake up radioiodine.

1Diagnosis of ThyroidCarcinoma• Usually asymptomatic except for apainless neck mass.
• “Cold” nodule on Tc-99m pertechnetate
scintigraphy.
• Non-cystic mass on ultrasound.
• Fine needle aspiration of nodule.

“Neuroendocrine” Tumors• Carcinoid Tumors• Pheochromocytoma• Neuroblastoma (mainly children)• Medullary Thyroid Carcinoma

Treatment of Carcinoid
Syndrome• Surgery• Embolization of liver metastases• I-131 MIBG
• Yttrium-90 Octreotide

Treatment of ThyroidCarcinoma• Surgical removal of thyroid gland anddissection of local lymph nodes.
• Total body diagnostic I-131 scan afterwithdrawal of thyroid hormone to detect
metastatic disease.
• I-131 sodium iodide, 150 – 200 millicuries
administered orally to ablate remaining
thyroid and metastases.

Carcinoid Tumors• Incidence: About 25 / million / year
• Most arise somewhere in the GI tract(75%) or lungs (25%).
• Usually small and do not cause
symptoms (benign).
• Malignant ones can metastasize to liver,bone and lung.

Non-Hodgkin’s Lymphoma• Incidence: About 200 / 100,000 per yearin U.S (7 – 8 times more common thanHodgkin’s Disease)• Average age at diagnosis: 60• Diffuse disease involving lymph nodes
and bone marrow• B-cell and T-cell types

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Treatment of Non-Hodgkin’sLymphoma• External beam irradiation of mantle fieldand/or pelvic lymph nodes• Chemotherapy• Immunotherapy with monoclonal
antibodies against B-cells (MAB)• Radioimmunotherapy: I-131 MAB or Y-90
MAB

The Reasons We Have Release
Regulations Are...

• To ensure that radiation exposure to
the public is ALARA.
• To reassure concerned members of
the public that the “risk” fromradiation patients is manageable andunder authoritative control.

Current Regulatory Criteria• Criteria are “risk-based” rather than“rules-based”.
• Can be adapted to other therapeutic
radionuclides, not just I-131.
• Flexible approach to determination of
expected dose to public.

Treatment with I-131 MAB• Serial images with I-131 MAB (5 mCi) to
determine total body clearance half-time.
• Titrate administered therapy activity
based on clearance half-time.
• Precede I-131 MAB with infusion of nonlabeled MAB.
• Administer 80 – 120 mCi via slow
intravenous infusion.

I-131 Patient Release:History• Prior to 1997, criteria for release werebased strictly upon activity or dose-rate.
• OK to Release if: < 30 millicuries, or < 5mrem per hour at one meter.
• After 1997, criteria based upon expectedradiation dose to a “member of thepublic” being < 500 millirem.

Current Regulatory
Requirements• Written Instructions on minimizing
exposure to others must be provided topatient if a member of the public could
receive > 100 mrem.
• Patient may be released if “public dose”,
as demonstrated by “default criteria” orby licensee’s computation, is < 500 mrem.

3Current Regulatory
Requirements

Where to Find Regulations andRegulatory Guidance• Written Documentation of release isrequired if licensee’s computation isbased on assumptions other thanthose underlying the “defaultcriteria”.
• Documentation must be maintainedby the licensee for three years.

• 10 CFR 35.75 , “Release of Individuals Containing
Unsealed Byproduct Material or Implants Containing
Byproduct Material”.

“Default” I-131 ReleaseCriteria• < 33 millicuries administered, or < 7
mrem/hr at one meter Æ FREE TO GO.
Need only written instructions (generic;provided by Nuclear Medicine).
• Based on: patient is an unshielded
point source, and only elimination is byphysical decay (conservative).

Licensee’s Computation– www.nrc.gov > Electronic Reading Room > Regulations (10 CFR)

• NUREG 1556, Vol. 9, Appendix U (formerly RegulatoryGuide 8.39)– www.nrc.gov > Electronic Reading Room > Document
Collections > NUREG-Series Publications“Default” I-131 Release
Criteria
D = 1.44 x T1/2 x O x R
D= “Public” dose
T1/2 = physical half-life (hr)O = Occupancy factor at one meter
R = Dose rate at one meter (mrem/hr)
For T1/2 = 196 hr, O = .25 and R = 7
mrem/hr, D = 500 mrem.

Licensee’s Computation⌠∞ R(t) dt
D = O⌡
0I-131 MIBG Clearance
1.2
1.0Fraction• May assume non-point source geometry.
• May assume tissue shielding.
• May take biological clearance intoaccount.
• May assume occupancy factor different
than 0.25 at one meter.

y = 0.8061e-0.0229x
R2 = 0.9253

0.80.60.4
0.2R(t) at 1 m0.00.0

50.0

100.0

150.0

Hours Post-administration

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External Dose From aThyroid Cancer Patient

What About Internal
Irradiation?

D = O ( 1.44 T1/2 R0 )D= “Public” dose
T1/2 = effective half-life (hr)O = Occupancy factor at one meter
R0 = Dose rate at one meter (mrem/hr)
R0

For T1/2 = 18 hr, O = 0.25 and R = 12
mrem/hr, D = 97 mrem.

What About Internal
Irradiation?

• Assume one part in 100,000 of the radioactivity
administered to patient (AA) is ingested by afamily member.
• Compute effective dose to family member fromingestion: D = 10-5 (AA) (53 rem/mCi)• If greater than 10% of computed external dose,must include it in total dose computation.

For Example...

• Avoid airplanes and buses at first.
• Limit interactions with others.
• Stay six feet or more away fromchildren and pregnant women.
• Spouse sleeps in a separate bed.
• Use separate bathroom.
• Shower / brush teeth frequently.

• Radioiodine from therapy patients may be
excreted in their urine, perspiration and saliva.
• These body fluids can contaminate household
surfaces.
• Family members might ingest thiscontamination through hand-to-mouth contact.

Instructions ShouldAddress...
• Public transportation.
• Children, pregnant women andnursing mothers.
• Spouse or spousal equivalent.
• Visitors and co-workers.
• Time-Distance considerations.
• Length of time to limit interaction.

How Long Should Patients
Limit Interaction?

• The higher the computed “generalpublic” dose, the longer the timecertain activities should be avoided.
• Times to avoid certain activities canbe calculated based on the estimated“public dose”.

5Maintaining Release Records• No record required if patient released
according to default criteria (< 33 mCi or
7 mrem/hr at one meter).
• Otherwise, release must be documented,
and the documentation maintained forthree years.
• Specific information regarding therelease must be included.

Duke’s Implementation of
Release Regulations

Release Record Must
Include...
• Patient identifier (NOT Name).
• Release activity and dose rate at one meter.
• Survey instrument used.
• Estimated “public” dose (mrem).
• Effective half-life used in computation of dose.
• Method used to compute dose.
• Times to limit certain activities.

The Radiation Safety Tech...

• Uses initial dose rate at one meter.
• Uses Duke population clearance curves fordifferent treatments.
• Data for a patient is entered into a Web site.
• Web site calculates expected “general public”
dose and creates a set of instructions anddocumentation.

• Interviews the patient to determine homesituation, transportation, work, visitors andcapacity for self-care.
• Obtains dose rate measurement at one meterfrom patient• Uses Web site to create “customized”
instructions and release documentation.
• Maintains documentation for three years.

Alternative to Web Site

What About Homeland Security?

• Interview patient, obtain effective half-life andmeasure dose rate.
• Look up “public dose” in pre-computed
tables and release patient if < 500 millirem.
• Look up length of time instructions are to befollowed in tables.
• Fill in pre-printed instruction form.

• Extremely sensitive radiation detectors aredeployed in train stations, airports, tunnels,etc.
• I-131 patients may set off alarms up to 95 days
following a procedure.*• Society of Nuclear Medicine recommends
giving patients letter containing radionuclide
and hospital contact information.
*Zukier LS, Stabin M, Garetano G, Monetti M, Lanka V. Presented at Annual
Meeting of RSNA, 30 November 2004.

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