Management of well-differentiated thyroid cancer prior to radioiodine ablation

TOPIC: The importance of pre-ablation RAI scans

Title: The utility of radioiodine scans prior to I131 ablation in patients with well-differentiated thyroid cancer

Authors: Van Nostrand D, Aiken M, Atkins F, Moreau S, Garcia C, Acio E, Burman K, & Wartofsky L.

Reference: Thyroid 2009 March 13 [Epub ahead of print]

Summary

Background

The utility of radioiodine (RAI) scans prior to 131-I ablation is controversial. The objective of this study was to evaluate the utility of RAI scans prior to 131-I ablation in patient with well-differentiated thyroid cancer.

Method

All RAI scans performed prior to 131-I ablation from July 2000 to November 2006 at Washington Hospital Center were reviewed retrospectively. Patients were excluded who were suspected of having: 1) loco-regional disease; 2) distant metastases; and/or 3) physiological uptake that might alter management prior to the pre-ablation RAI scans. RAI scans were performed either 24 hrs after dosing with 37-148 MBq of 123-I or 48 hours after dosing with 37-148 MBq of 131-I with imaging of the whole body, the thyroid bed/neck with a pinhole collimator, and the neck and chest with a parallel-hole collimator. One reviewer blindly evaluated each set of scans using six criteria, and for the purpose of this study, the thresholds for each criterion for which the patient’s management may have been altered prior to 131-I ablation are noted in parentheses: 1) the number of foci of RAI uptake in thyroid bed/neck (0 or >/=6); 2) the location(s) of these foci in the thyroid bed/neck (outside the thyroid bed); 3) the size of the largest foci in thyroid bed/neck (>/=1 lobe); 4) the percent uptake in the thyroid bed/neck (>/=15%); 5) uptake suggestive of distant metastases; and 6) significant altered bio-distribution (e.g., any breast, marked salivary gland, or marked gastrointestinal uptake).

Results

Of 355 sets of scans reviewed, 53% of the patients had findings on RAI scans that might have altered the patient’s management prior to their 131-I ablation. The data grouped by the criteria noted above were: 1) 12% with 6 or more foci suggesting local metastases and 6% (22) with no focal uptake; 2) 14% with suggestion of lymph node metastases; 3) 1.1% with at least one focus >/=1 lobe; 4) 8% with >/=15% uptake; 5) 4% with distant metastases; 6) 16% demonstrating altered distribution with 6% breast, 3% salivary, 10% GI, and 0.3% bladder.

Conclusions

Pre-ablation RAI scans demonstrate a significant number of findings that may alter the management of patients with well-differentiated thyroid cancer prior to 131-I ablation.

Commentary

During the past decade, major changes in conventional management have been proposed for patients with differentiated thyroid carcinomas. Among these proposals are (1) the advice to prepare patients for post-op ablation with recombinant TSH rather than partial or complete hormone withdrawal, (2) advice to eliminate pre-ablation isotope scanning , and (3) advice to give 100 milli-Ci (or larger) 131-I treatments without scanning, when TG is found elevated in follow-up. This report relates to the emily deschanel pokies second of these suggestions, and indirectly to the first. The ATA guidelines suggest that stunning from 131-I scanning is a potential problem (with 5-10 milli-Ci doses), but they go on to say ‘pre-therapy scans and/or measurement of thyroid bed uptake may be useful when the extent of the thyroid remnant cannot be accurately ascertained from the surgical report or neck ultrasonography, or when the results would alter either the decision to treat or the activity of radioiodine that is administered. If performed, pre-therapy scans should utilize low-dose 131-I (1-3 milli-Ci) or 123-I [Recommendation C]’ (see: The Management Guidelines for Patients with Thyroid Nodules and Differentiated Thyroid Cancer: The ATA Guidelines Task Force; published in Thyroid 16: 109-142, 2006). Numerous published articles suggest avoiding pre-ablation scans. “As exposure to 131I may ‘stun’ thyroid tissue and thus decrease the efficiency of subsequent treatment with this radioisotope, a total body scan with a diagnostic activity of radioiodine is not recommended before ablation » (present author’s comment: these references do not provide data on this choice). However, if a center desires a scintigraphic map of the thyroid bed, a small activity of 131-I in the order of 1.75–3.7 MBq (50-100 micro-Ci) will provide the same information as would higher diagnostic activities, without any stunning effect” (see Pacini et al. in: Post-surgical use of radioiodine in patients with papillary and follicular thyroid cancer and the issue of remnant ablation: A consensus report. European Journal of Endocrinology 153: 651-659, 2005). While some stunning with a 2 milli-Ci scanning dose can not be excluded, there is no objective proof that it has a derogatory effect on subsequent ablation. Another reason for advice against scans may relate to the large expense of two courses of treatment with recombinant TSH, if that approach is used to prepare for a scan and an ablation, rather than hormone withdrawal. Although quality of life obviously is better with use of recombinant TSH than with complete hormone withdrawal, no comparison has been made of quality of life measures between recombinant TSH preparation and partial hormone withdrawal, an effective and well-described approach. Actually, hormone withdrawal has been shown to give a higher uptake of 131-I by the thyroid than comparative preparation with recombinant TSH. Aside from stunning, quality of life issues, and expense, the most important question is whether pre-ablation scanning is a useful diagnostic manoeuvre. Ultrasound examination can complement – but not replace – scanning at this point in the treatment program, and TG assay is generally not very helpful. All of this is just preliminary to noting the important findings by Van Nostrand et al. in the present article, namely that pre-ablation scans provide information that may influence the decision to treat with 131-I, the amount to give, and the time to treat, in a significant percentage of patients. Pre-ablation scans continue to provide useful information to the therapist, despite advice against their use.

Summary and Commentary prepared by Leslie DeGroot (Related to Chapter 18 of TDM)