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Frank P. Dawry Thyroid Cancer Therapy Radioactive Iodine (I-131)
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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
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Imaging findings ~10% of nodules are hot nodules
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Thyroid Nodules Workup one approach <1cm 6m Follow-up >1cm Fine Needle Biopsy Benign Papillary Ca Follicular Lesion Surgery
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Post Surgical Ablation Performed to eliminate competition for I-131 by malignant cells throughout the body
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Beta Particle Therapy
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Benefit of RAI ablation Thyroglobulin (Tg) Can Be Used As A Tumor Marker After A Successful Ablation >10 ng/ml = elevated above normal
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Post Ablation Imaging 7-10 days following ablation dose Too much tissue!
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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)
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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 12-14 days Low iodine diet for 7-10 days
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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
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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
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Dosimetry D Ʃ = Dβ + Dγ
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PET-probe Guided Surgery Useful in finding Iodine negative carcinoma
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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
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Patient release >33 millicuries administered
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Bioassay Florida State Regulation: 64E-5.625 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.
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