Frank P. Dawry Thyroid Cancer Therapy Radioactive Iodine (I-131)

Types of Thyroid Cancer  Papillary or Papillary-Follicular  Most common type;  Slow growing  Single encapsulated tumor  Spreads to regional lymph nodes, later lung and bone.  Follicular  Less common  More aggressive  Metastasizes via the blood stream  Hurthle Cell Tumor – similar to follicular but does not concentrate I- 131  Medullary  Originates in the parafollicular C-cells  Little or no I-131 concentration  Anaplastic  Dedifferentiated papillary or follicular cancer  Locally invasive with regional spread and early distant metastases  Little or no I-131 concentration  About 75% of Thyroid Cancers are Papillary and Papillary/follicular  About 15% are Follicular and Hurthle cell  About 7% are Medullary  About 3% are Anaplastic

Imaging findings ~10% of nodules are hot nodules

Thyroid Nodules Workup one approach <1cm 6m Follow-up >1cm Fine Needle Biopsy Benign Papillary Ca Follicular Lesion Surgery

Post Surgical Ablation Performed to eliminate competition for I-131 by malignant cells throughout the body

Beta Particle Therapy

Benefit of RAI ablation Thyroglobulin (Tg) Can Be Used As A Tumor Marker After A Successful Ablation >10 ng/ml = elevated above normal

Post Ablation Imaging 7-10 days following ablation dose Too much tissue!

RAI Ablation laboratory workup  TSH  Thyroglobulin (Tg) baseline  CBC  Serum BUN/creatinine  Urinalysis  Serum calcium  BETA HCG (serum pregnancy test - in women of child bearing age)  Chest X-ray (to screen for pulmonary mets)

RAI Ablation Patient preparation  Near total thyroidectomy  Discontinue Thyroxine (T4) 6 weeks prior to treatment to cause an increase in TSH  (goal >30-50 uIU/ml)  T3 substituted for the first 3-4 weeks and then discontinue for days  Low iodine diet for 7-10 days

Treatment Guidelines Ablation  30 to 75 millicuries I-131 or more.  <30 millicuries traditionally used to avoid patient being admitted  30,000 rad to the remnant  Requires individual dosimetry

Metastases Treatment Guidelines Empirical  Beierwaltes protocol -  Local metastases  75 to 150 millicuries  Distal metastases  150 to 300 millicuries Dosimetric  Benua -  Blood samples, and whole-body counts to determine retention and clearance rates to determine the maximum safe dose  Delivers no more than 2 Gy (200 rad) to the whole blood  Whole-body 48 hour retention rate < 120 millicuries (4440 MBq)  <80 millicuries (2960) with pulmonary metastases  Maxon  Thyroid remnant – 8,000 rad to nodal metastases

Dosimetry D Ʃ = Dβ + Dγ

PET-probe Guided Surgery Useful in finding Iodine negative carcinoma

Patient release >33 millicuries administered The maximum likely dose to an individual exposed to the patient [D (mrem)] must be less than 500 millirem – if not, patient must be hospitalized until less than 30 millicuries or exposure rate at 1 meter is <5 mR/hour

Patient release >33 millicuries administered

Bioassay  Florida State Regulation: 64E Safety Instruction and Precautions for Radiopharmaceutical Therapy, Brachytherapy, and Teletherapy.  measure the thyroid burden of each individual who helped prepare or administer a dosage of liquid iodine 131 within 3 days after administering the dosage.  Nuclear Regulatory Commission, Part 35  requires that, for staff who helped prepare or administer a dosage of 131I to patients who were hospitalized for compliance with the patient-release criteria, a measurement of thyroid burden must be made within three days of such administration.