در مرکز پزشکی هسته ای دکتر دباغ – دکتر صادقی در خدمت شما هستیم مشهد، ملاصدرا 11 ، پلاک 1/4 www.DSNMC.ir Tel:+98(51) 38411524; +98(51)38472927
Nuclear Medicine In Thyroid gland (Brief) V. R. Dabbagh Kakhki, M.D. Nuclear Medicine Specialist Associate Professor DSNMC Nuclear Medicine Research Center (NMRC; MUMS) www.DSNMC.ir www.mums.ac.ir/nmrc
Thyroid ScanTc99m- 131I- 123I Left Cold Nodule
Thyroid Scan: Multinodular goiter with retrosternal extension
Thyroid Scan: Thyroglossal Cyst
Total Thyroidectomy After 4-6 weeks Ablation 1 week dxWBS 2 months TSH 4 moths: (6 M) Follow-up
Radioiodine Therapy : RAIT for • Thyroid remnants • Microscopic DTC • Nonresectable DTC • Incompletely resectable DTC • Metastatic Lesions • Two main forms of the procedure. • Radioiodine ablation: post-surgical • Radioiodine Treatment
Radioiodine ablation: post-surgical • Eliminate thyroid remnants to increase the sensitivity and specificity of follow-up testing: Tg and of diagnostic whole-body scintigraphy (dxWBS). • Ablation also allows sensitive “post-therapy” whole-body scintigraphy (rxWBS) that may detect previously occult metastases and serves to treat any microscopic tumour deposits. • May reduce long-term morbidity and mortality
Ablation success • Evaluated 6–12 months after the ablation procedure : criteria: • on follow-up dxWBS, negative thyroid bed uptake or thyroid bed uptake beneath an arbitrarily set, low threshold, e.g. 0.1%, • absence of detectable thyroid-stimulating hormone-(TSH-) stimulated Tg antibodies has been excluded, • absence of suspicious findings on neck ultrasonography
Radioiodine Treatment • Nonresectable or incompletely resectable lesions • Microscopic disease, • Macroscopic local tumour • Lymph node or distant metastases, either as a component of primary treatment of DTC or to address persistent or recurrent disease.
Radioiodine ablation after total or near-total thyroidectomy is a standard procedure in patients with DTC. • The only exception is patients with: • unifocal papillary thyroid carcinoma ≤1 cm in diameter who lack: • evidence of metastasis, • hyroid capsule invasion, • history of radiation exposure, • unfavourable histology: tall-cell, columnar cell or diffuse sclerosing subtypes. In these cases without the above risk factors, completion thyroidectomy or RAIT of large remnants may be avoided.
If total or near-total thyroidectomy: • Some centers refrain from radioiodine ablation: Prognosis? • Other centers consider radioiodine ablation as a means of improving follow-up and potentially decreasing relapse risk;
Contraindications Absolute 1. Pregnancy 2. Breastfeeding Relative Before the potential RAIT, clinically relevant: 1. Bone marrow depression, if administration of high 131I activities is intended. 2. Pulmonary function restriction, if a significant pulmonary 131I accumulation is expected in lung metastases. 3. Salivary gland function restriction, especially if 131I accumulation in known lesions is questionable. 4. Presence of neurological symptoms or damage when inflammation and local oedema caused by the RAIT of the metastases could generate severe compression effects.
Stunning • Diminution of RAIT uptake and efficacy due to suboptimal therapeutic effects, biological effects, or both, of prior diagnostic radioiodine administration. • In cases where RAIT clearly will be necessary, pre-therapeutic 131I dxWBS or thyroid bed uptake measurement should be avoided because their results will not modify the indication for RAIT and these procedures may induce stunning.
Stunning • To reduce the possibility of stunning when it is not yet known whether RAIT is indicated, thyroid bed uptake quantification or 131I dxWBS performed before the potential RAIT should employ low radioiodine activities. • Recommended quantities are approximately 3–10 MBq for uptake quantification and 10–185 MBq for WBS. • Alternatively, use of 40–200 MBq of 123-iodine (123I) for diagnostic imaging minimises the risk of stunning. However, the lower imaging sensitivity and higher cost of 123I compared with 131I are disadvantageous.
Patients should be advised to discontinue breast feeding for 6–8 weeks before radioiodine administration. • Conception should be avoided by means of effective contraception for 6 months after RAIT
Alternative or additional treatments Besides surgery , treatments that may be used instead of or in addition to RAIT include : • Cytotoxic chemotherapy: doxorubicin monotherapy • External beam radiotherapy (XRT), The main settings for these treatments are late-stage, progressive DTC or symptomatic or progressive lesions that are unresectable and that have failed to respond to RAIT or are unlikely to do so.
Traditional indications for XRT in the DTC setting • Nunresectable gross disease, • Gross tumours left behind after operation, • Gross evidence of local invasion • Tracheal invasion even when only microscopic disease remains. • Painful bone metastases • Metastases in critical locations likely to result in fractures or neurological or compressive symptoms, if these lesions are not amenable to surgery
Differentiated thyroid carcinoma:Tg • Levels more than 2ng/ml in patients after 131I treatment is very sensitive and specific for recurrence • 20% of recurrences can be missed if we obtain Tg without adequate TSH rising(80 vs. 100%) • Tg is not accurate in the presence of anti-thyroglobulin Abs (all serums should be checked)
Differentiated thyroid carcinoma:Imaging • WBS with 131I is 95% specific and 50-70% sensitive • Post 131I treatment can increase sensitivity about 45% • WBS+Tg has sensitivity of 85-100%
Differentiated thyroid carcinoma:Imaging (non-Iodine tracers) • Includes: 18F-FDG,201Tl,99mTc agents • May be more useful in: • Non-Iodine avid tumors • Non-hypothyroid patients • Patients with expanded Iodine pool
Differentiated thyroid carcinoma:Imaging (non-Iodine tracers) • 201Tl is 60-90% sensitive for metastatic DTC • 99mTc-sestamibi is highly sensitive for lymphadenopathy but not lung mets • 18F-FDG is much better than the two previous tracers
Differentiated thyroid carcinoma:Treatment (dose consideration) • Thyroid bed:100 mCi • Cervical LN: 150-175 mCi • Lungs: 175-200 mCi • Bones: 200 mCi
Differentiated thyroid carcinoma:Follow up • TSH, T4,T3, CBC, Plt at 4w • T4,TSH,Tg at 8w • WBS every year or 6 mo • After 2 negative WBS every 2-5 years • Tg every 6 mo • TSH should be undetectable in high risk patients
Differentiated thyroid carcinoma:Follow up : TSH • >0.1 for high risk patients • 0.1-0.5 for low risk patients • Persistent disease <0.1 • In patients who are clinically and biochemically free of disease but who presented with high risk disease: TSH 0.1-0.5 for 5–10 years. • In patients free of disease, especially those at low risk for recurrence, the serum TSH may be kept within the low normal range (0.3–2). • In patients who have not undergone remnant ablation who are clinically free of disease and have undetectable suppressed serum Tg and normal neck US, the serum TSH may be allowed to rise to the low normal range (0.3–2mU/L).
Differentiated thyroid carcinoma:Re-treatment • 6 mo-1 year interval between treatments is recommended • Low grade positive WBS and stable Tg after several re-treatments only needs follow up with Tg • No fixed upper limit for 131I dose exists
rhTSH The approved regimen of rhTSH is two consecutive daily intramuscular injections of 0.9 mg. Radioiodine is given 1 day and serum Tg testing is performed 3 or 4 days after the second rhTSH injection.
Left image shows uptake of 131I in the thyroid bed. Right image is follow-up scan one year after 131I treatment demonstrating successful ablation of that remnant. There is physiological activity in the bowel in both images and bladder in the right image
uptake of 131I in functioning metastases in cervical lymph nodes and faintly in the lungs