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Evaluation of^99mTc-MIBI Scintigraphy in the Postsurgical Patients with DTC

Author: QiuLiHeng
Tutor: LinYanSong
School: Beijing Union Medical College
Course: Medical Imaging and Nuclear Medicine
Keywords: differentiated thyroid carcinoma 99m~Tc-MIBI radionuclide imaging RAI dedifferentiated thyroid cancer
CLC: R736.1
Type: Master's thesis
Year: 2011
Downloads: 42
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Abstract

99mTc-methoxyisobutylisonitrile(99mTc-MIBI, or MIBI) has been reported to show high sensitivity in detecting metastases of differentiated thyroid cancer (DTC), especially the non-radioiodine avid metastases which tend to be dedifferentiated. The aim of this study is to evaluate whether 99mTc-MIBI scintigraphy can be used in surveillance of the postsurgical patients with DTC. There are two sections in this study:Section 1 Research on application of 99mTc-MIBI scan compared with 131I whole-body scan to the postsurgical patients with DTCObjective:To evaluate the complementary role of 99mTc-MIBI to 131I whole-body scan in patients with initial radioactive iodine (RAI) treatment and in monitoring dedifferentiated metastases. Methods:A prospective study of 69 patients randomized picked out from 316 DTC patients in nuclear medicine department, PUMCH, from April 2009 to April 2010. They underwent 99mTc-MIBI regional and whole-body scan. The results of 99mTc-MIBI scan were compared mainly with the 131I whole-body scan 1 week after RAI therapy. The study of 99mTc-MIBI images included visual and semi-quantitative analysis. Visual study was done by two experienced nuclear medicine physicians without clinical findings and the results of other imaging. Semi-quantitative studies were done by calculating the tumor-to-background (t/b) ratio of metastases and non-metastases in lung, the lung metastases were confirmed by either high-resolution CT or post RAI 131I scan. The data were analyzed by SPSS 13.0 software. Results:1 patient who died of angiosarcoma was excluded. The patients were categorized into 2 groups according to RAI therapy for analysis. Group A(n=46,21 had metastases):prepare for initial RAI ablative therapy after thyroid surgery. Group B (n=22,11 had metastases):need further RAI treatment, duo to suspected elevated Tg level or residual metastases after initial RAI therapy. In group A,99mTc-MIBI scan detected thyroid remnants in 37.0% patients (17 of 46) and metastatic foci in 33.3% patients(7 of 21). In group B,99mTc-MIBI scan detected recurrent and metastatic foci in 63.6% patients (7 of 11). The thyroid remnants and metastatic focus accumulating the 99mTc-MIBI or not was simplified as MIBI+/MIBI-, likewise for 131I was I+/I-.5 patients (7.4%) had three types of metastases according to 99mTc-MIBI and 131I scan:MIBI+I-, MIBI-I+, and MIBI+I+. The status that the metastases have different presentation in concentrating 99mTc-MIBI and 131I was defined as the’mismatch’such as MIBI+I-, MIBI-I+. We divided the patients into two groups (non-metastatic and metastatic groups in lung), t/b ratio (p>0.05) showed no significant difference between two groups.Conclusion:99mTc-MIBI scan has limited utility in detecting thyroid remnants and functioning metastases, but it has advantages over 131I scan to discriminate lymph nodes and non-functioning metastases which tends to be dedifferentiated.Section 2:Study of 99mTc-MIBI positive cases and mismatch of 99mTc-MIBI and 131I scanObjective:Considering the clinical data such as medical history, imaging data and RAI therapy response, to determine the clinical significance of 99mTc-MIBI positive cases, and the mismatch of 99mTc-MIBI and 131I scan.Methods:A retrospective study of 44 cases selected from 112 patients with clinical data, imaging (99mTc-MIBI scan,131I scan, CT, bone scan,18F-FDG PET/CT scan) and laboratory data (TSH, Tg) from April 2009 to March 2011. According to the results of the 99mTc-MIBI and 131I scan, the patients with metastases were divided into four groups (MIBI+I+, MIBI+I-, MIBI-I+, MIBI-I-) in order to evaluate the significance of 99mTc-MIBI scan. Results: According to previous groups, cases in MIBI+I+, MIBI+I-, MIBI-I+, MIBI-I-among patients with metastasis were 4,11,27 and 2, respectively. In surveillance of metastatic cases, Tg level of MIBI+I+group was retained>1000ng/ml before and after RAI therapy, suggesting relative bad response to RAI therapy and some tumor cells tend to be dedifferentiated; while MIBI+I-group had a mild raise, suggesting worse response to RAI therapy and the tumor cells turn to be dedifferentiated; Tg level of MIBI-I+ group had a remarkable decrease after RAI therapy, suggesting good response to RAI therapy. Furthermore, we find 99mTc-MIBI scan had a good consistency with F-FDG PET scan, however, as the limitation of relative lower resolution of SPECT,99mTc-MIBI detected less foci than that of 18F-FDG PET scan. Moreover, the periodic 99mTc-MIBI scan might provide useful information of the metastases in patient follow-up. Conclusion: Combination of 99mTc-MIBI scan and 131I scan could afford comprehensive biological information of the metastases, and could identify dedifferentiated lesions irresponsive to RAI and foretell RAI therapy response. It might be a substitute of F-FDG PET, which is still not available for routine imaging (?)wadays in China.The above two sections showed that:Due to the low sensitivity of (?)MIBI scan in detecting thyroid remnants and functioning differentiated metastases, it cannot be used as a substitute of 131I scan. However the combination of 99mTc-MIBI scan with 131I scan could offer more diagnostic information than either. In addition,99mTc-MIBI scan is better than 131I scan in detecting the non-functioning dedifferentiated metastases, which might be a promising imaging alternative of the expensive 18F-FDG PET scan.

Evaluation of99mTc-MIBI Scintigraphy in the Postsurgical Patients with DTC

Abstract

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Evaluation of^99mTc-MIBI Scintigraphy in the Postsurgical Patients with DTC