|Year : 2015 | Volume
| Issue : 1 | Page : 8-13
Incremental value of 131 I SPECT-CT versus planar whole body imaging in patients with differentiated thyroid carcinoma
Ajit S Shinto1, KS Deepu1, KK Kamaleshwaran1, Firoz Rajan1, KS Rajkumar1, P Velayutham1, G Govindaraju2, Suresh Venkatachalam3, M Vimala Kannan4
1 Department of Nuclear Medicine, Kovai Medical Center and Hospital, Coimbatore, India
2 Department of Surgical Oncology, Har Shamitra Superspeciality Cancer Center and Research Institute, Trichy, India
3 Department of Surgical Oncology, Sheela Hospital, Coimbatore, India
4 Department of Surgical Oncology, Aadhi Medical Foundation Pvt Ltd, Coimbatore, Tamil Nadu, India
|Date of Web Publication||18-Dec-2014|
Dr. Ajit S Shinto
Department of Nuclear Medicine, Kovai Medical Center and Hospital, Coimbatore - 641 014, Tamil Nadu
Source of Support: None, Conflict of Interest: None
Objectives: To evaluate the incremental diagnostic value of iodine-131 single-photon emission computed tomography/computed tomography ( 131 I SPECT-CT) compared to planar scintigraphy in patients with differentiated thyroid carcinoma (DTC). Materials and Methods: The study group consisted of 117 patients (Age group = 7-81 yrs; 70 females, 47 males) with DTC; post total thyroidectomy. A diagnostic dose of 111 Mbq (3 mCi) 131 I was administered and planar scan obtained after 48 hrs. Foci of uptake in planar scan were classified as thyroid remnants, lymph nodes, lung metastases, skeletal metastases, distant metastases or of indeterminate etiology. Single-photon emission computed tomography/computed tomography (SPECT-CT) of these areas was then acquired on a dual head gamma camera and reclassification was done. Results: Planar scans depicted 218 foci of 131 I activity classified as 194 neck foci and 24 distant foci. Incremental value of SPECT/CT compared with planar imaging was found for 72 of 194 neck lesions (37.1%) and 24 of 24 distant foci (100%) for a total of 95 of 218 iodine avid foci (44%). SPECT/CT findings led to down staging of 44 of the 72 foci from equivocal or lymph nodes to thyroid remnant and upstaging of 18 of the 72 foci from equivocal or thyroid remnant to lymph node involvement. An additional 8 of the 72 foci were reclassified as physiologic dental or salivary gland activity. The remaining 2 of the 72 foci was found out to be contamination on patient's skin. Conclusion: 131 I SPECT-CT provides increased diagnostic information compared with planar imaging alone, which may alter the patient management.
Keywords: 131 I, localization, SPECT CT, thyroid cancer, whole body scans
|How to cite this article:|
Shinto AS, Deepu K S, Kamaleshwaran K K, Rajan F, Rajkumar K S, Velayutham P, Govindaraju G, Venkatachalam S, Kannan M V. Incremental value of 131 I SPECT-CT versus planar whole body imaging in patients with differentiated thyroid carcinoma. Thyroid Res Pract 2015;12:8-13
|How to cite this URL:|
Shinto AS, Deepu K S, Kamaleshwaran K K, Rajan F, Rajkumar K S, Velayutham P, Govindaraju G, Venkatachalam S, Kannan M V. Incremental value of 131 I SPECT-CT versus planar whole body imaging in patients with differentiated thyroid carcinoma. Thyroid Res Pract [serial online] 2015 [cited 2022 Aug 17];12:8-13. Available from: https://www.thetrp.net/text.asp?2015/12/1/8/147276
| Introduction|| |
Differentiated thyroid carcinoma (DTC) is the most common endocrine cancer among adults (1.1% of cancer diagnoses per annum).  The most common cancer type was papillary, followed by follicular cancer.  With the exception of unifocal micro carcinoma, with no extension beyond the thyroid capsule and without lymph node metastases (LNM), the standard treatment for DTC includes total thyroidectomy and therapy with 131 I-iodide. With this combined approach, 5 years of survival rates exceed 90% overall. ,
The demonstration or exclusion of metastases in the regional lymph nodes play a major role since all the patients with LNMs are attributed to the high-risk group. 
LNM can be detected by elective neck dissection. However, elective neck dissection is not carried out in a number of patients with DTC. , Furthermore in a minority of patients, LNM may elude surgical removal. 
In our center, routine 131 I diagnostic studies are carried out to complete postoperative staging of disease and guide selection of radioiodine therapy. Many physicians choose to omit the diagnostic 131 I study and proceed directly to fixed dose radioiodine therapy. An inherent problem with this method is the inability to complete staging until after the patient has received the therapeutic dose of radioiodine.
Our interest was to ascertain whether hybrid single-photon emission computed tomography/computed tomography (SPECT/CT) technology, compared with planar imaging would facilitate characterization of residual thyroid tissue, enabling informed decisions on the treatment. The aim of this study was to investigate the importance of 131 I SPECT/CT fusion imaging in the evaluation of central neck and distant foci of radionuclide activities in a group of images composed of diagnostic 131 I scans.
| Materials and Methods|| |
At our institution, all patients who undergo total thyroidectomy routinely undergo diagnostic 131 I scanning 4-5 weeks after the operation to complete staging before the first dose of radioiodine therapy is administered. Based on staging information, incorporating clinical, histopathological, and imaging data, the 131 I therapy dose is adjusted according to the patient's risk classification. Our protocol typically involves administration of 100-125 mCi (3.7-4.6 GBq) for thyroid remnant ablation, 150 mCi (5.6 GBq) for regional nodal disease, 200-300 mCi (7.4-11.1 GBq) for distant metastasis.
Whole body and static neck images were obtained at 24/48 hours post administration of a diagnostic dose of 37 MBq (1 mCi) for the first-time radioiodine treatment patients and 111 MBq (3 mCi) for patients who had already undergone prior radioiodine treatment. Further evaluation was done by acquiring SPECT/CT images for patients who showed foci tracer uptake in the planar images. We have found out that SPECT/CT is useful in providing information for indications such as characterization of equivocal central neck activity, anatomic localization of distant metastatic foci, identification of regional LNM, evaluation of suspected physiologic mimics of disease and assessment of discrepancies between planar imaging and histopathological and biochemical data. A post-therapy scan obtained 7 days later is used to assess for additional foci of activity compared to the diagnostic scan.
Patient selection criteria
This retrospective study, included 117 patients (70 women, 47 men; 29.15 years, 7-81 years) with DTC and had undergone recent total thyroidectomy. The histologic types were follicular thyroid carcinoma (n = 27), papillary thyroid carcinoma (n = 77), follicular variant of papillary carcinoma (n = 10) and Hurthle cell carcinoma (n = 3). All the above mentioned patients underwent diagnostic I131 studies. SPECT/CT was done for all patients during the diagnostic scan. After the therapy, they went through post-therapy planar imaging. However, post-therapy SPECT/CT was not performed in most cases as additional foci were rarely identified. Four patients underwent both diagnostic and post-therapy SPECT/CT for evaluation of differences between radioiodine distribution on the diagnostic and post-therapy planar images.
The 131 I whole body planar and static neck images were acquired in both anterior and posterior projections with a dual head gamma camera (Symbia True Point SPECT/CT, Siemens Medical solutions) with parallel hole high energy collimators and a 20% energy window set at 364 keV. The table speed for the whole body images was 8 cm/s. SPECT/CT images were acquired in the same camera with 16 steps per head (20 s/stop), non-circular orbit over 360 degrees, and a 128 × 128 matrix. Standard reconstruction technique entailed Flash 3D ordered subset expectation maximization iterative reconstruction with four iterations and eight subsets and a CT-based attenuation corrected algorithm applied to the SPECT images. Low dose CT parameters consisted of 130 kV and 100 mA. Reconstruction was performed at 5 mm slice thickness on a 512 × 512 matrix and a field view of 53.3 × 38.7. Patients were imaged with their arms down without immobilizers.
Study design and image interpretation
The 131 I scans were viewed independently by two nuclear medicine physicians who are experienced in reading radioiodine scans.
All planar images were evaluated for foci of uptakes. First, the foci of uptake, interpreted as localized in the thyroid bed, were identified; these were then classified as thyroid remnants. Foci separable from these thyroid remnants were then identified and classified. A focus close to the thyroid bed, as indeterminate; and a focus at a greater distance from thyroid bed, as LNM. Foci seen elsewhere in the body were classified as distant metastases.
SPECT/CT was then carried out for the same regions and the foci were later reclassified.
| Results|| |
Planar scans depicted 218 foci of 131 I activity classified as 194 neck foci and 24 distant foci [Table 1]. At SPECT/CT, these foci were further classified as thyroid bed remnants, lymph node metastatic lesions, contamination, physiologic activity and distant metastasis.
An additional diagnostic value was found in 72 of 194 foci, defined as a change in focus classification. SPECT/CT findings led to correct down staging of 44 of 72 foci from equivocal or LNM to thyroid remnant and correct upstaging of 18 of 72 foci from equivocal or thyroid remnant to LNM. An additional 8 of 72 foci were reclassified as physiologic dental or salivary activity. The remaining 2 of 72 foci was found out to be a contamination on patient's skin.
SPECT/CT brought about no change in the classification of the 24 distant foci. The final classification was 9 bone metastatic lesions, 12 lung metastatic lesions and mimics 3 physiologic diseases. SPECT/CT, however, enabled superior anatomic localization of activity in cases of bone metastasis, allowing exclusion of skin contamination with certainty. In all cases of distant metastasis, although, there was no change in focus classification, SPECT/CT improved lesion localization, provided additional anatomic information, and increased reader confidence. Therefore, incremental value of SPECT/CT compared with planar imaging was found for 72 of 194 central neck lesions (37.1%) and 24 of 24 distant foci (100%) for a total of 95 of 218 131 I foci (44%).
| Discussion|| |
This paper details the incremental diagnostic value of SPECT/CT over planar imaging in 117 patients with DTC. SPECT/CT helped correctly downstage 61.1% of indeterminates or LNM lesions to thyroid remnants [Figure 1] and further, helped upstage 25% of thyroid remnants or indeterminate foci to LNM [Figure 2]. SPECT/CT also helped correctly identify physiologic activity [Figure 3] and contamination on patient skin. Although, there was no change in the classification of distant metastases, improved localization and anatomical accuracy of lesions were brought about by SPECT/CT [Figure 4] and [Figure 5]. Compared to planar imaging, SPECT/CT thus yielded a total gain in information of 44% of the patients leading to a different patient management.
The superiority demonstrated by SPECT/CT in our patients clearly agree with previously published data obtained from more heterogeneous groups of patients. ,
|Figure 1: Anterior planar wholebody 131I image (a) showing uptake in the residual thyroid tissue (long arrow) and possible right cervical lymph node (short arrow). Corresponding axial CT (b), SPECT (c) and fused SPECT/CT (d) showing uptake localized to the right residual functioning thyroid tissue|
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|Figure 2: Anterior planar wholebody 131I image (a) showing uptake in residual thyroid tissue and? Right cervical node (arrow). Corresponding axial CT (b), SPECT (c) and fused SPECT/CT (d) confirms uptake localized to the lower cervical lymph node|
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|Figure 3: Anterior planar wholebody 131I image (a) showing asymmetric uptake in the region of left upper neck,? Left cervical node. Corresponding axial CT (b), SPECT (c) and fused SPECT/CT (d) showing focus localized to the physiologic uptake in the left submandibular gland|
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|Figure 4: Posterior planar wholebody 131I image (a) showing uptake in the chest. Corresponding sagittal CT (b), SPECT (c) and fused SPECT/CT (d) localizes the uptake to the D4 vertebra lytic lesion with soft tissue component|
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|Figure 5: Anterior planar wholebody 131I image (a) showing uptake in the thyroid remnant (long arrow) and multiple foci in the chest (short arrow). Corresponding axial CT (b), SPECT (c) and fused SPECT/CT (d) showing uptake localized to the lung nodules (short arrow)|
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The 131 I SPECT/CT is accurate for characterization of activity foci identified on planar images and when applied to a diagnostic, 131 I study allows completion of TNM staging and risk stratification based on the patient's disease burden.
In 2004, Tharp et al., reported that SPECT/CT had an incremental diagnostic value, compared with planar imaging, in 57% of the thyroid patients with thyroid carcinoma in a retrospective study.  A similar study by Wong K K et al., reported a higher incremental diagnostic value of 70.7% with the use of SPECT/CT.  Another study by Chen et al., conducted in 66 patients, SPECT/CT showed incremental value over planar imaging in increasing diagnostic accuracy, reducing pitfalls, and modifying therapeutic strategies in 73.9% of the patients. In addition, the role of SPECT/CT in DTC patients has been described in a few case reports, including detection of benign struma ovarii in a patient with invasive papillary thyroid cancer,  renal metastases from follicular thyroid cancer,  retention in Warthin's tumor  and retained radioiodine in the respiratory tract of a papillary thyroid carcinoma. 
Our study indicated that lesions can be identified by planar scanning in majority of patients and that SPECT/CT after planar scanning should be considered in select patients showing inconclusive planar scan results. Although, we describe the additional benefits of SPECT/CT in the management of DTC, it should always be used in conjunction with planar imaging and not as a standalone diagnostic tool.
Benefits of fusion 131 I SPECT/CT
The availability of SPECT/CT has been of a great influence in our nuclear therapy clinical practice. Various shortcomings of planar 131 I imaging such as low resolution, and a scarcity of anatomic information along with a long list of physiologic variants makes image interpretation difficult. In order to differentiate between physiologic and pathologic foci, multiple methods such as swallowing water, oblique and lateral imaging, washing the patient's skin and reacquiring, correlating with other imaging techniques are to be carried out. There is also a need to ensure pitfalls such as dentures, handkerchiefs, and other sources of contamination are avoided to make an accurate diagnosis. In our experience, 131 I SPECT/CT has facilitated a fast, accurate, and reliable assessment of radioiodine activity found outside the expected bio distribution. On SPECT/CT images, central neck activity is characterized as thyroid remnant or loco regional disease, and the number of equivocal foci on planar assessment is reduced. In the detection of distant metastatic disease, the superior lesion localization and additional CT-derived anatomic information obtained with SPECT/CT increase reader's confidence and helping clinical management decisions.
Limitations of fusion 131 I SPECT/CT
Despite the many benefits of 131 I SPECT/CT, we have faced certain technical problems and challenges in our experience when applying this technology to diagnostic radioiodine scintigraphy. Considerable mis-registration of functional and anatomic data was seen. Generally, integrated SPECT/CT cameras image patients in the same bed position during the same session to achieve image fusion. In practice, however, patient movement on the bed continues to occur and may be only limited with immobilizers. The difficulty with 131 I SPECT/CT is the lack of background tissue activity on functional images, which facilitates recognition of mis-registration. However, we use salivary gland activity as a check for registration by ensuring alignment of activity to the correct anatomic location of the glands. Mis-registration may also be related to the fusion software used and may arise from the use of different header information on tomographic data from different vendors.
SPECT with low amperage CT also adds a radiation dose ranging from 1 to 2 mSv to that of radioiodine. However, we feel that the risk brought about by this, gets considerably outweighed by the benefits due to hybrid imaging.
Another limitation of our study was that no histopathologic tests were carried out to confirm the nature of lesions confirmed through SPECT/CT, as they were not deemed necessary in the present clinical context.
We have also found that planar images are very useful, if not essential for interpretation of SPECT/CT images. Problems encountered with SPECT of low-level 131 I activity included poor spatial resolution that blurred two adjacent foci seen distinctly on planar images, reconstruction of septal penetration activity into discrete foci, streak artefacts due to reconstruction of intense 131 I activity, and attenuation of central neck activity by the shoulders. We, therefore, support the view that SPECT/CT images should always be interpreted in conjunction with planar images and not in isolation.
From 2011 until 2013, 91% of all patients referred to our institution for radioablation were also studied using SPECT/CT. The reason for not examining the remaining 9% was no definite foci of uptake noted in the planar scan or the unsuitability of the patient for this procedure, as would be the case in a severely ill patient or uncooperative patient. The group we studied may therefore be considered representative of the all patients being referred to our hospital.
| Conclusion|| |
Iodine-131 SPECT/CT provides greatly increased diagnostic information compared to that obtained with planar imaging alone. This information can be used for accurate characterization of central neck activity, superior localization of distant metastatic lesions, evaluation and rapid confirmation of suspected physiologic mimics of disease, and increasing reader's confidence. By upstaging or downstaging disease, SPECT/CT may alter the management of patients with thyroid carcinoma.
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