|Year : 2016 | Volume
| Issue : 1 | Page : 178-180
Diagnostic whole body scan (pre-therapy scan) in differentiated thyroid cancer: A single center community hospital experience
P Santhanam1, HK Driscoll2, P Venkatraman3
1 Department of Medicine, Section of Endocrinology, Joan C Edwards School of Medicine, Marshall University, Huntington, WV 25701, USA
2 Department of Endocrinology, Joan C Edwards School of Medicine, Marshall University, Huntington, WV 25701, USA
3 Tristate Primary Care, Ashland, Kentucky 41101, USA
|Date of Web Publication||28-Apr-2016|
Department of Medicine, Section of Endocrinology, Joan C Edwards School of Medicine, Marshall University, Huntington, WV 25701
Source of Support: None, Conflict of Interest: None
Objective: Diagnostic whole body scan (pre-therapy scan) with either I-123 or I-131 (radioactive isotopes of iodine) is performed to assess the extent of thyroid cancer especially distant metastasis prior to administering the therapeutic dose of I-131. Our aim of the following study was to determine the utility of the diagnostic pre-therapy scan in the management of differentiated thyroid cancer. Materials and Methods: It was a case-control study carried out by retrospective chart review, of a randomly selected 100 patients with differentiated thyroid cancer who had followed in our community hospital over the course of 1 year. We collected data on multiple variables in the subjects - including age, gender, pre-operative size of the nodules, diagnosis, stage of the malignancy, size of the tumor, multifocality, lymphovascular invasion, dose of radioiodine used for remnant ablation, recurrence rates and persistence rates. Continuous variables were compared using the independent sample Mann-Whitney U-test whereas the Chi-square test was used for nominal variables. Results: The mean dose of radioactive iodine administered was 97.56 (±27.98) in the pre-therapy scan group and it was 97.23 (±32.40) in the control group. There was no difference between the two groups (P - 0.45). There was also no difference in the recurrence rates between the groups (P = 1.0). There was a trend toward a higher degree of persistent cancer in the group that had the pre-therapy scans (P - 0.086). Conclusion: Pre-therapy scan may not affect the dose of radio-iodine I-131 used for remnant ablation of differentiated thyroid cancer and does not influence the recurrence rates. This was especially true with respect to I-131 remnant ablation for low risk tumors.
Keywords: Differentiated thyroid cancer, I-131 therapy, pre-therapy scan,
|How to cite this article:|
Santhanam P, Driscoll H K, Venkatraman P. Diagnostic whole body scan (pre-therapy scan) in differentiated thyroid cancer: A single center community hospital experience. Indian J Cancer 2016;53:178-80
|How to cite this URL:|
Santhanam P, Driscoll H K, Venkatraman P. Diagnostic whole body scan (pre-therapy scan) in differentiated thyroid cancer: A single center community hospital experience. Indian J Cancer [serial online] 2016 [cited 2020 Dec 1];53:178-80. Available from: https://www.indianjcancer.com/text.asp?2016/53/1/178/180853
| » Introduction|| |
Radioiodine ablation of the thyroid remnant after total thyroidectomy for differentiated thyroid cancer is standard clinical practice. Recent studies as well as guidelines have implied that radioactive iodine (RAI)-131 may be of little benefit for low risk tumors. However prior to the guidelines; most thyroid experts were aggressive in treating remnant tissue with I-131 to ease the detection of recurrence and follow-up of the patients.
Prior to the American Thyroid Association (ATA) differentiated thyroid cancer management guidelines, it was unclear if pre-therapy whole body scan (WBS) (imaging prior to remnant ablation with I-131) would add to the diagnostic value and treatment of differentiated thyroid cancer. In our clinic, it was usually performed for high risk tumors in order to roughly determine the dose of RAI needed to be administered. In contrast, some high risk tumors were treated with a higher dose of radioiodine empirically. Low risk tumors usually received an empirical low dose of radioiodine I-131. Sometimes, even low risk tumors received a pre-therapy diagnostic WBS with I-123. The revised ATA guidelines recommends pre-therapy scan (with a very low dose of either I-123 or I-131), if it would alter the management plan - with a grade C level of recommendation.
We performed a retrospective chart review of patients with differentiated thyroid cancer and examined the different variables and their relation to I-123 pre-therapy diagnostic WBS.
| » Materials and Methods|| |
We examined 100 randomly selected cases of thyroid cancer from our hospital and performed a retrospective chart review of the patients. They had been seen in our clinic as a regular follow-up visit in a single year. Prior approval was obtained from the Marshall University Institutional review board. Since it was a chart review of randomly selected 100 patients with thyroid cancer - data on all the variables was not available for all patients. Persons with anaplastic cancer, medullary thyroid cancer and multiple endocrine neoplasia were excluded from the study. We collected data on multiple variables in the subjects including demographic data-age, gender, pre-operative size of the nodules, diagnosis, stage of the malignancy, size of the tumor, multifocality, lymphovascular invasion, extrathyroidal extension, dose of radioiodine used for remnant ablation, recurrence rates and persistence rates. Recurrence was defined as one of the following; A biopsy proven thyroid carcinoma in a patient previously disease free for over 6 months, a positive I-123 and/or I-131 WBS in a patient known to have no previous positive uptake scan and an elevated serum thyroglobulin over 10 ng/ml after a T4 withdrawal study or greater than 5 ng/ml after a recombinant-thyroid - stimulating hormone administration. Persistent disease was defined as; incomplete resection with known residual tumor, an elevated serum thyroglobulin which has never fallen below 2 ng/ml. We considered age, pre-operative size of nodules, size of the tumor and the dose of radioiodine I-131 used for remnant ablation as continuous variables. Gender, diagnosis, multifocality, lymphovascular invasion, extra thyroidal extension, presence of recurrence and/or persistence were treated as nominal variables. Appropriate precautions were taken to protect the patient identity with de-identifiers.
The baseline characteristics were compared for the case group (with pre-therapy scan) with the control group (without pre-therapy scan). SPSS was used for statistical analysis. The continuous variables were compared using the independent sample Mann-Whitney U-test whereas the Chi-square test was used for nominal variables. The α level was set at 0.05.
| » Results|| |
There were 34 cases of papillary, 3 cases of follicular and 3 cases of other rare variants (tall cell and Hurthle cell) in the pre-therapy scan group. There were 49 cases of papillary, 1 case of follicular and 4 cases of other variants in the control group. The distribution of the diagnostic subgroups was no different between the two groups (P - 0.23).
The baseline characteristics of the groups have been listed in [Table 1]. There was no difference in the case and the control group in the baseline characteristics. There was a trend towards higher incidence of lymphovascular invasion in the pre-therapy scan group (P - 0.19).
The mean dose of RAI administered was 97.56 (±27.98) in the pre-therapy scan group and it was 97.23 (±32.40) in the control group. There was no difference between the two groups (P - 0.45) [Graph 1]. There was also no difference in the recurrence rates between the groups (P = 1.0). There was a trend toward higher degree of persistent cancer in the group that had the pre-therapy scan (P - 0.086). Patients who had the pre-therapy scan also had more number of metastatic recurrences but the difference did not reach clinical significance [Graph 2].
| » Discussion|| |
Total body scan in the pre-ablation stage was initially studied using 201-thalium and it was able to pick some lesions which were missed in the scan done after ablative therapy even though the post-ablation scan was better in many cases.
There have been studies comparing different isotopes of iodine and their respective doses for use in pre-therapy scan of patients with differentiated thyroid cancer. In one study, 74 MBq I-131 used for pre-therapy imaging yielded the same ablation rate as that of 14.8 MBq of I-123 (the usual isotope for pre-therapy scan) for similar doses of I-131 used for ablation. Even though the diagnostic accuracy may be higher with the I-131 pre-therapy scan, it has much more profound effects on stunning.
Some studies have suggested a very high impact of stunning with pre-therapy scan while others have implied that the effect is overemphasized., Furthermore the dose administered for remnant ablation varies widely according to the practice. Some studies have shown better results with doses as much as 3.7 GBQ as compared to 1.1 GBQ. Others have suggested that lower doses are as good as higher doses.
Our study in a random set of 100 patients seems to suggest that the pre-therapy scan does not affect the recurrence rates. Furthermore it does not impact the dose of radioiodine used for ablation. There was a trend towards higher incidence of lymphovascular invasion in the pre-therapy scan group but the sample size was small and there may have been a propensity to do pre-therapy scan in those individuals with lymphovascular invasion. In addition, there was a trend towards increased persistence in the pre-therapy scan which may be either due to their higher risk (selection bias) versus the stunning effect of I-123 or I-131 used for the same. Also, the patients who had the pre-therapy scan tended to have metastatic recurrences.
There are certain limitations in our study. It was a retrospective chart review and the duration of follow-up was different for individual patients. Also the sensitivity of the thyroglobulin assay has changed over time leading to differences in the assay used for detection of recurrence or persistence. Some patients have received more than one dose of I-131 for the ablation of residual or persistent disease which complicates the picture.
Most of the tumors in our practice were low risk and since these may not benefit with RAI therapy, these may not benefit with pre-therapy scan either.
| » Conclusion|| |
Pre-therapy scan may not have much utility in most cases of differentiated thyroid cancer and may have some stunning effect leading to lower ablation rates and higher recurrences. This is especially true for low risk malignancies.
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