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Radiology Life • February 2017

11 | ADVANCE FOR RADIOLOGY LiFE | CANCER THERAPY Current Standard of Care in RAI Following a thyroidectomy, guidelines established by the American Thyroid Association indicate that use of remnant ablation involving administration of RAI can be considered, even among a select group of low-risk patients. However, the benefits of using RAI to reduce the risk of recurrence following thyroidectomy are not firmly established for all patients, especially among those with low-risk papillary thyroid cancer (PTC). Many of these patients achieve a TSH-stimulated thyroglobulin (Stim-Tg) less than 1 μg/L following total thyroidectomy alone, making remnant ablation unnecessary to reliably follow thyroglobulin as a tumor marker.3,4,5,6,7 Further, the literature does not report a definitive benefit for RAI in decreasing the rates of recurrence or death in lowrisk PTC.8,9,10 Despite questions about its usefulness, recommendations for RAI administration remain broad for low- and intermediate-risk PTC patients, with no objective criteria on which to base the recommendation for ‘selective use.2,11,12 Rates of RAI administration rose from 1990 to 200813, largely due to these broad guideline recommendations as well as physician-held beliefs regarding the potential benefits of RAI.14 In an effort to restrict use of RAI among patients where it may be unlikely to provide benefit in reducing risk of recurrence, researchers have worked to develop a personalized strategy for risk stratification and RAI administration in low- and intermediate-risk PTC based on a patient’s postoperative pathology, Stim-Tg and neck ultrasound Stim-Tg Protocol.4 Several retrospective studies15,16 and two prospective studies4,6 have supported the utility of post-operative Stim-Tg in selecting patients for RAI therapy, and its ability to safely avoid unnecessary radiation, especially among those with a Stim-Tg less than 1 μg/L. Moreover, two large systematic reviews have confirmed the high negative predictive value (NPV) of post-operative Tg for future disease-free status, measured during TSH stimulation17 and during levothyroxine therapy using an ultrasensitive assay.18 However, despite the increasing recognition of post-operative Tg’s high NPV in predicting future disease-free status, long-term prospective experience on RAI selection criteria using Tg and neck ultrasound remains limited. In an effort to develop clearer guidance related to use of RAI in low- and intermediate-risk thyroid cancer patients, our team has extended the follow-up of patients in our previous prospective study3,4 to 6.2 years.19 These observations support the utility of a personalized risk stratification and RAI selection protocol (PRSP) which uses serial post-operative Stim-TG and neck ultrasound results in PTC patients.19 About the Study Participants in the study all underwent total or subsequent completion thyroidectomy. Only patients with low- and intermediate-risk PTC followed from 2006 to 2013 were included in this study. Low- and intermediate-risk was defined as all PTC nodules equal or greater than 1 cm (T1–T3), confined to the thyroid or central (level VI) lymph nodes (N0–N1a), irrespective of patient age or tumor size. Exclusion criteria included (1) tumors less than 1 cm given that their risk for PTC recurrence was defined as very low, (2) detectable anti-thyroglobulin antibodies (TgAb) given their potential interference with the thyroglobulin (Tg) assay, (3) lateral compartment lymph node involvement (N1b), and (4) extrathyroidal extension (T4) or distant metastases (M1). Relevant demographic, surgical, pathologic, biochemical, treatment, clinical and outcome data were collected. The benefits of using RAI to reduce the risk of recurrence following thyroidectomy are not firmly established for all patients.” FEBRUARY 2017


Radiology Life • February 2017
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