Educational Objectives • Introduce participants to the medical conditions that are Releasing Nuclear Medicine treated with radioiodine. • Review the regulatory considerations regarding Patients to the Public: inpatient and outpatient radioiodine procedures. Dose Calculations and Discharge • Review ways in which the regulatory requirements may be satisfied, including “public” radiation dose Instructions computations, content of post-discharge instructions and addressing the concerns of patients and their families. Robert E. Reiman, MD Radiation Safety Division • Introduce Web-based methods to facilitate Duke University Medical Center documentation of outpatient treatment. Durham, NC Medically Useful Iodine Isotopes Treatment of Toxic Goiter Isotope Half-life Primary Use Emissions I-123 13.3 hours γ (0.158 MeV) Diagnosis • Surgery (not done, except for very large thyroid, low iodine uptake, cancer or I-124 4.2 days β+ and γ (0.511 Diagnosis, pregnancy) MeV +) Therapy(?) I-125 59.4 days γ (0.035 MeV) Brachytherapy • Drugs (propylthiouracil) and beta blockers (short-term) I-131 8.0 days β- (0.606 MeV), Diagnosis, • Ablation with radioactive iodine γ (0.364 MeV) Therapy Radioiodine Treatment Thyroid Carcinoma • I-131 sodium iodide solution, orally • 8 – 15 millicuries for diffuse toxic goiter • Incidence: about 3 per 100,000 per year • 15 – 40 millicuries for toxic multinodular • Females > Males (2:1) goiter • About 80% papillary type; remainder • Must know the % uptake at 24 hours to follicular or medullary types. compute administered activity and • Medullary thyroid carcinoma does not clearance rates take up radioiodine. 1 Diagnosis of Thyroid Treatment of Thyroid Carcinoma Carcinoma • Surgical removal of thyroid gland and • Usually asymptomatic except for a dissection of local lymph nodes. painless neck mass. • Total body diagnostic I-131 scan after • “Cold” nodule on Tc-99m pertechnetate withdrawal of thyroid hormone to detect scintigraphy. metastatic disease. • Non-cystic mass on ultrasound. • I-131 sodium iodide, 150 – 200 millicuries • Fine needle aspiration of nodule. administered orally to ablate remaining thyroid and metastases. “Neuroendocrine” Tumors Carcinoid Tumors • Carcinoid Tumors • Incidence: About 25 / million / year • Most arise somewhere in the GI tract • Pheochromocytoma (75%) or lungs (25%). • Usually small and do not cause • Neuroblastoma (mainly children) symptoms (benign). • Medullary Thyroid Carcinoma • Malignant ones can metastasize to liver, bone and lung. Treatment of Carcinoid Non-Hodgkin’s Lymphoma Syndrome • Surgery • Incidence: About 200 / 100,000 per year in U.S (7 – 8 times more common than • Embolization of liver metastases Hodgkin’s Disease) • Average age at diagnosis: 60 • I-131 MIBG • Diffuse disease involving lymph nodes • Yttrium-90 Octreotide and bone marrow • B-cell and T-cell types 2 Treatment of Non-Hodgkin’s Treatment with I-131 MAB Lymphoma • External beam irradiation of mantle field • Serial images with I-131 MAB (5 mCi) to and/or pelvic lymph nodes determine total body clearance half-time. • Titrate administered therapy activity • Chemotherapy based on clearance half-time. • Immunotherapy with monoclonal • Precede I-131 MAB with infusion of non- antibodies against B-cells (MAB) labeled MAB. • Radioimmunotherapy: I-131 MAB or Y-90 • Administer 80 – 120 mCi via slow MAB intravenous infusion. The Reasons We Have Release I-131 Patient Release: Regulations Are... History • Prior to 1997, criteria for release were • To ensure that radiation exposure to based strictly upon activity or dose-rate. the public is ALARA. • OK to Release if: < 30 millicuries, or < 5 • To reassure concerned members of mrem per hour at one meter. the public that the “risk” from • After 1997, criteria based upon expected radiation patients is manageable and radiation dose to a “member of the under authoritative control. public” being < 500 millirem. Current Regulatory Criteria Current Regulatory Requirements • Written Instructions on minimizing • Criteria are “risk-based” rather than exposure to others must be provided to “rules-based”. patient if a member of the public could • Can be adapted to other therapeutic receive > 100 mrem. radionuclides, not just I-131. • Patient may be released if “public dose”, • Flexible approach to determination of as demonstrated by “default criteria” or expected dose to public. by licensee’s computation, is < 500 mrem. 3 Current Regulatory Where to Find Regulations and Requirements Regulatory Guidance • Written Documentation of release is • 10 CFR 35.75 , “Release of Individuals Containing Unsealed Byproduct Material or Implants Containing required if licensee’s computation is Byproduct Material”. based on assumptions other than – www.nrc.gov > Electronic Reading Room > Regulations (10 CFR) those underlying the “default criteria”. • NUREG 1556, Vol. 9, Appendix U (formerly Regulatory Guide 8.39) • Documentation must be maintained – www.nrc.gov > Electronic Reading Room > Document by the licensee for three years. Collections > NUREG-Series Publications “Default” I-131 Release “Default” I-131 Release Criteria Criteria • < 33 millicuries administered, or < 7 D = 1.44 x T1/2 x O x R mrem/hr at one meter Æ FREE TO GO. Need only written instructions (generic; D= “Public” dose T1/2 = physical half-life (hr) provided by Nuclear Medicine). O = Occupancy factor at one meter • Based on: patient is an unshielded R = Dose rate at one meter (mrem/hr) point source, and only elimination is by For T1/2 = 196 hr, O = .25 and R = 7 physical decay (conservative). mrem/hr, D = 500 mrem. Licensee’s Computation Licensee’s Computation ∞ D = O ⌠ R(t) dt ⌡0 • May assume non-point source geometry. I-131 MIBG Clearance 1.2 • May assume tissue shielding. 1.0 y = 0.8061e-0.0229x 0.8 R2 = 0.9253 • May take biological clearance into 0.6 account. Fraction 0.4 0.2 • May assume occupancy factor different R(t) at 1 m 0.0 0.0 50.0 100.0 150.0 than 0.25 at one meter. Hours Post-administration 4 External Dose From a What About Internal Thyroid Cancer Patient Irradiation? D = O ( 1.44 T1/2 R0 ) • Radioiodine from therapy patients may be D= “Public” dose excreted in their urine, perspiration and saliva. T1/2 = effective half-life (hr) O = Occupancy factor at one meter • These body fluids can contaminate household R0 = Dose rate at one meter (mrem/hr) surfaces. For T = 18 hr, O = 0.25 and R = 12 • Family members might ingest this R 1/2 0 mrem/hr, D = 97 mrem. contamination through hand-to-mouth contact. What About Internal Instructions Should Irradiation? Address... • Public transportation. • Assume one part in 100,000 of the radioactivity • Children, pregnant women and administered to patient (AA) is ingested by a nursing mothers. family member. • Spouse or spousal equivalent. • Compute effective dose to family member from ingestion: D = 10-5 (AA) (53 rem/mCi) • Visitors and co-workers. • If greater than 10% of computed external dose, • Time-Distance considerations. must include it in total dose computation. • Length of time to limit interaction. For Example... How Long Should Patients Limit Interaction? • Avoid airplanes and buses at first. • Limit interactions with others. • The higher the computed “general • Stay six feet or more away from public” dose, the longer the time children and pregnant women. certain activities should be avoided. • Spouse sleeps in a separate bed. • Times to avoid certain activities can • Use separate bathroom. be calculated based on the estimated “public dose”. • Shower / brush teeth frequently. 5 Maintaining Release Records Release Record Must Include... • No record required if patient released according to default criteria (< 33 mCi or • Patient identifier (NOT Name). 7 mrem/hr at one meter). • Release activity and dose rate at one meter. • Otherwise, release must be documented, • Survey instrument used. • Estimated “public” dose (mrem). and the documentation maintained for • Effective half-life used in computation of dose. three years. • Method used to compute dose. • Specific information regarding the • Times to limit certain activities. release must be included. Duke’s Implementation of The Radiation Safety Tech... Release Regulations • Interviews the patient to determine home • Uses initial dose rate at one meter. situation, transportation, work, visitors and • Uses Duke population clearance curves for capacity for self-care. different treatments. • Obtains dose rate measurement at one meter • Data for a patient is entered into a Web site. from patient • Web site calculates expected “general public” • Uses Web site to create “customized” dose and creates a set of instructions and instructions and release documentation. documentation. • Maintains documentation for three years. Alternative to Web Site What About Homeland Security? • Extremely sensitive radiation detectors are deployed in train stations, airports, tunnels, • Interview patient, obtain effective half-life and etc. measure dose rate. • I-131 patients may set off alarms up to 95 days • Look up “public dose” in pre-computed following a procedure.* tables and release patient if < 500 millirem. • Society of Nuclear Medicine recommends • Look up length of time instructions are to be giving patients letter containing radionuclide followed in tables. and hospital contact information. • Fill in pre-printed instruction form. *Zukier LS, Stabin M, Garetano G, Monetti M, Lanka V. Presented at Annual Meeting of RSNA, 30 November 2004. 6.