☢️ Scintigrafie Whole-Body cu Iod-131 în Cancerul Tiroidian Diferențiat

Updated Thyroid I-131 Scan 9/8/2024 ●Indications  To assess for the presence of and localization of any functioning residual, recurrent, or metastatic differentiated thyroid carcinoma after thyroidectomy or before/after I-131 ablation and for surveillance. ●Radiopharmaceutical: Diagnostic Imaging - 1-4 mCi I-131 sodium iodine capsule administered by mouth Hyperthyroidism Ablation - 5-15 mCi I-131 sodium iodine capsule administered by mouth Thyroid Cancer Therapy - 30-150 mCi I-131 sodium iodine capsule administered by mouth ●Patient Preparation: No specific preparation prior to radionuclide administration. ●Conflicting Examinations/Medications: The following substances should be withheld for the indicated time frames as they can interfere with the uptake of radioiodine: ◦levothyroxine (Synthroid) - 4 wks ◦amiodarone - 3-6 mths ◦liothyronine (Cytomel) - 2 wks ◦iodine-containing medication/preparation - 4 wks ◦methimazole (Thiamazole) - 3-7 days ◦Lugol's / SSKI solution - 4-6 wks ◦carbimazole - 3-7 days ◦perchlorate - 1 wk ◦propylthiouracil (PTU) - 3-7 days ◦kelp - 4 wks Iodinated IV contrast musted be avoided for 3-4 wks. A low-iodine diet should be followed for 1-2 weeks. Diet adequacy can be confirmed with an AM spot urine iodine level. TSH level should be ≥30 mIU/L accomplished by either thyroid hormone withdrawal or rhTSH (Thyrogen) stimulation. A patient may be maintained on T3 until 10–14 days prior to ablation to avoid severely symptomatic hypothyroidism. ●Pregnancy/Lactation:  A negative urine pregnancy test is required in potentially-pregnant patients prior to I-131 administration. See Pregnant, Potentially Pregnant and Lactating Patients policy for specifics. Pregnancy should be avoided for 6 mths following I-131 administration.  Breast feeding mothers should discontinue breast feeding 6 wks (preferably 3-6 mths) prior to I-131 administration and should not resume breast feeding the current child. Breast feeding can resume with the next child. ●Imaging Technique: Collimator - medium energy high resolution Photopeak - 364 keV 15% window for I-131 Image Preset Counts ◦Whole Body Images - 8-10 cm/min ◦Static Images - 10-20 mins/image Matrix Size - 256 x 1024 (whole body), 256 x 256 (static) Zoom - 2.67 Patient Positioning - supine ●Imaging Views: Imaging is obtained at 24 hrs and 48-72 hrs after diagnostic imaging doses and usually at 2-7 days after ablative doses. Obtain anterior and posterior whole body images. Obtain anterior static images centered on the neck (from nasopharynx to upper chest) with chin and sternal markers present. ●Notes:  Thyroglobulin (Tg) is used as a tumor marker in differentiated thyroid cancer after total thyroidectomy and radioiodine ablation. Typically a Tg level <1.0 ng/mL indicates remission, while a level >10 ng/mL indicates persistent disease. Tg antibody is a class G immunoglobulin and can also be elevated in recurrent thyroid cancer.  Metastatic thyroid cancer has lower density of and poorer functioning of Na-I symporters. TSH elevation over time is important to promote increased RAIU and retention in tumors. rhTSH-stimulated scans failed to detect remnant cancer localized to the thyroid bed in 17% of patients and metastatic disease in 29% in whom it was detected after thyroid hormone withdrawal.

thyroid bed in 17% of patients and metastatic disease in 29% in whom it was detected after thyroid hormone withdrawal.  Tg elevation after rhTSH stimulation is 3–5 times less than that obtained after thyroid hormone withdrawal, which may result in suboptimal evaluation of post operative / post ablation disease burden.  Diagnostic RAI imaging may reveal unexpected iodine-avid metastatic disease in 22%–35% of cases and change management in approximately 30%–50% of cases.  Diagnostic RAI imaging is useful in determining the I-131 dose for ablation. Larger doses are usually given for treatment if regional or distant metastases are detected on the pre ablation scan. Only 1% of total thyroidectomies are truly total.