Description:
FDG-SPECT, also referred to as metabolic SPECT (single photon emission computed tomography), or PET using a gamma camera, is a general term describing imaging techniques in which a SPECT gamma camera is used to detect the paired 511 ke-V photons emitted from decaying positrons associated with the metabolism of radiolabeled 2-fluoro-2 deoxy-D-glucose (FDG), a radiotracer commonly used in PET (positron emission tomography) imaging. SPECT cameras are conventionally used to provide scintigraphic studies such as bone scans or cardiac thallium studies. When used in conjunction with FDG, specially equipped SPECT cameras can provide images reflecting the metabolic activity of tissues, similar to PET scanning.

Dedicated PET scanners consist of multiple detectors arranged in a full or partial ring around the patient, permitting the simultaneous detection of the high-energy paired photons that are emitted at 180 degrees from one another. The clinical value of PET scans is related both to the ability to image the relative metabolic activity of target tissues and the resolution associated with PET scanners. The expense of on-site manufacture of the FDG is prohibitive for most facilities. That, coupled with the expense of the PET scanner itself, has limited the widespread availability of PET scanning. However, radiolabeled FDG has a relatively long half-life of 110 minutes, permitting off-site manufacture at distribution centers with transport to nearby facilities. Thus, the lack of PET scanners may be emerging as the critical limiting factor to further diffusion of PET imaging. In response, researchers have begun to investigate whether the more readily available SPECT cameras, routinely used to detect low-energy photons, could be adapted for use to detect higher energy photons emitted from positrons.

FDG-SPECT imaging describes 2 general techniques. In 1 technique, SPECT cameras are adapted with collimators that screen out the lower energy photons and, thus, only detect the high-energy 511 ke-V photons. For the purposes of this policy, this technique will be referred to as FDG-collimated-SPECT. However, this approach decreases the sensitivity and resolution compared to that associated with PET scanners. In a second technique, a dual-headed rotating SPECT camera can be operated in the "coincidence mode," meaning that the camera will only count those photons that are simultaneously detected at 180 degrees from one another. This technique will be referred to as FDG-DHC (dual-head coincidence)-SPECT. PET scanners also rely on coincidence detection, and thus FDG-DHC-SPECT more closely resembles a PET scanner. However, the lower number of detectors in the SPECT approach compared to the full or partial ring of detectors used in PET imaging will result in a relative loss of sensitivity and resolution. An additional technical challenge is the use of sodium iodide crystals, which scintillate in response to bombardment by photons. In SPECT cameras, these crystals have been optimized to detect lower energy photons used in routine nuclear medicine studies and not the high-energy photons associated with FDG. These technical issues raise questions regarding the diagnostic performance of FDG-SPECT in comparison to PET scanning. Oncologic and cardiac applications have been most thoroughly studied.

Note: Conventional PET scanning is considered separately in Policy Nos. 60120, 60126 and 60106, addressing the cardiac, oncologic and other applications of PET scans, respectively.

Policy:
FDG-SPECT may be considered MEDICALLY NECESSARY as a technique to evaluate myocardial viability in patients with known coronary artery disease, specifically patients with severe left ventricular dysfunction who are under consideration for a revascularization procedure.

Other cardiac applications of FDG-SPECT are investigational/unproven therefore considered NOT MEDICALLY NECESSARY, including, but not limited to, the following:

• Coronary artery perfusion defects and other cardiac applications
• Known or suspected malignancies
• Motor neuron and other neurological disorders
• Dementias
• Psychiatric disorders
• Attention deficit disorder  

Policy Guidelines
Patient selection criteria for evaluation of myocardial viability
Candidates for assessment of myocardial viability are typically those patients with severe left ventricular dysfunction who are under consideration for a revascularization procedure. A PET, FDG-SPECT or thallium SPECT scan may determine whether the left ventricular dysfunction is related to viable or non-viable myocardium. Patients with viable myocardium may benefit from revascularization, while those with non-viable myocardium will not.

The following CPT code describes PET as a technique to assess myocardial viability (i.e., metabolic imaging)

CPT code
78459: Myocardial imaging, positron emission tomography (PET) metabolic evaluation.

The above CPT code essentially describes the physician work (i.e., interpretation component) of the PET scan. Institutions may code for the preparation of the radiopharmaceutical and the scan itself by using the "TC" modifier (i.e., technical component modifier) in conjunction with the above CPT code. However, if the radiopharmaceutical is supplied by an outside distribution center, there may be a separate charge for this component, distinct from the scan itself. In addition, there may be an additional transportation cost if the radiopharmaceutical is not manufactured on the premises. When charged separately, the radiopharmaceutical may be coded using the appropriate HCPCS code for the supply.

Specific coding for FDG-SPECT would require coding for the SPECT scan in conjunction with distinct coding for the radiopharmaceutical separate from the scan itself. However, all CPT codes describing SPECT scans include their clinical use (i.e., studies of wall motion, etc.), and no code describes the use of a SPECT scan to determine metabolic activity.

In 2006, a specific HCPCS code for FDG was added:
A9552: Fluorodeoxyglucose F-18 FDG, diagnostic, per study dose, up to 45 millicuries

Benefit Application
BlueCard/National Account Issues
FDG-SPECT may be difficult to identify if the test is coded as if it is a conventional PET scan. Therefore, plans may want to consider the use of specific, distinct coding schemes for FDG-SPECT, either using the combination of existing codes for PET, SPECT and radiopharmaceuticals (see policy guidelines, above), or advising use of the HCPCS S code.

Cardiac Applications
For assessment of myocardial viability, conventional PET, FDG-SPECT and thallium SPECT scans provide equivalent diagnostic information in most clinical situations. According to the guidelines of the American College of Cardiology (J Am Coll Cardiol 1995; 25:521-47), in routine situations, thallium SPECT scans are generally preferred over PET scans due to their lower price. Therefore, plans may want to consider if their benefits or contractual language support a management strategy of steering patients to the lowest price option. It should be noted that in certain markets, PET and thallium SPECT scans may be competitively priced.

• FDG-SPECT represents complicated billing issues, and different plans may experience different billing practices.
• In some plans, the isotope may be billed separately from the scan, making it difficult to distinguish between an FDG-SPECT scan and a conventional SPECT scan.
• In some plans, the hospital (Blue Cross) component may be billed separately or billed through a Revenue code, both creating difficulties in identifying FDG-SPECT.
• Some plans without a dedicated PET scanner in their market may consider FDG-SPECT eligible for coverage, but at a negotiated rate based on a percentage of the CPT code for PET tumor imaging.
• Some plans have identified specific institutions that perform FDG-SPECT and, thus, implement the policy by flagging the institution.

Rationale
FDG-SPECT imaging has been most extensively studied in 2 settings where conventional PET scanning has accepted clinical applications: oncologic applications and assessment of myocardial viability. (See policy Nos. 60126 and 60120 for cardiac and oncologic applications of PET scanning, respectively.) For oncologic applications, the diagnostic performance of FDG-SPECT scanning must be evaluated in 2 settings; i.e., first, as an alternative to conventional PET scanning when PET facilities are locally available, and, second, as an alternative to anatomic imaging techniques (typically CT scanning or MRI) when conventional PET scanning is not locally available. In assessing myocardial viability, FDG-SPECT scans must be compared to PET scans or conventional SPECT scans. Conventional thallium SPECT scanning reflects myocardial viability on the basis of cell membrane integrity, while, in contrast, PET scanning assesses myocardial viability on the basis of metabolic integrity. However, as discussed in a separate policy on cardiac applications of PET scanning (policy No. 60120), the diagnostic performance of conventional PET and SPECT are considered clinically equivalent in the majority of cases.

Oncologic Applications
Both FDG-collimated-SPECT and FDG-DHC-SPECT have been evaluated in oncology patients. However, the early experience with FDG-collimated-SPECT suggested a significantly inferior performance of FDG-collimated-SPECT compared to PET scanning, and, thus, this technique has largely been abandoned in favor of FDG-DHC-SPECT.^1,2 Representative studies using FDG-DHC-SPECT are reviewed here.

Tatsumi and colleagues reported on a study of 23 patients with newly diagnosed lung cancer who were examined with both conventional PET and FDG-DHC-SPECT on the same day. Although FDG-DHC-SPECT detected 22 of the 23 lung nodules, since this study only included patients with known lung cancer, it does not duplicate the typical clinical application of PET as a technique to evaluate an indeterminant pulmonary nodule.³ Weber and colleagues reported on a case series of 96 patients who underwent FDG-DHC-SPECT scanning to evaluate pulmonary lesions with a mean size of 3.44 cm based on chest X-ray or CT scan.⁴ Patients were selected for the study only if they were scheduled to undergo biopsy. Therefore, while the FDG-DHC-SPECT studies were compared to histopathologic diagnosis, the patient population had a higher prevalence of malignancy (90%), compared to the usual 40% – 60% prevalence of malignancy in patients presenting with indeterminate lung lesions undergoing conventional PET scanning. The overall sensitivity and specificity of FDG-DHC-SPECT in diagnosing malignant lesions was 97% and 80%, respectively. CT scans were performed in 93 of the 96 patients. The sensitivity and specificity of CT scans in detecting malignancy was 99% – 100% and 29% – 38%, respectively, suggesting that compared to CT scanning, FDG-DHC-SPECT may have increased specificity. However, the authors note that the specificity of CT in this study is considerably lower than the 60% that is reported in the literature. The small number of benign lesions may explain the lower specificity in this series.

Delbeke and colleagues reported on a case series of 26 patients, 19 of whom had known or suspected malignancies in various sites.⁵ All patients underwent both FDG-DHC-SPECT and conventional PET within one half-hour of each other. Among the 19 oncology patients, FDG-DHC-SPECT identified only 28 of the 38 lesions identified by conventional PET scanning. Shreve and colleagues reported on a case series of 31 patients with known or suspected malignancies who underwent imaging with both conventional PET and FDG-DHC-SPECT.⁶ All images were read blindly. PET results were considered the gold standard. Of a total of 109 discrete lesions depicted by conventional PET scanning, only 60 were identified by FDG-DHC-SPECT, for a relative sensitivity of 55%. The relative sensitivity of FDG-DHC-SPECT was highest in the lung (FDG-DHC-SPECT correctly identified 13 of 14 lesions) and lowest in the abdomen (FDG-DHC-SPECT correctly identified only 6 of 23 lesions). The superior performance of FDG-DHC-SPECT in the lung compared to other sites may be related to the relatively low background noise in the lungs, which maximize contrast for pulmonary nodules. When background noise is higher, detection of small nodules (< 1.5 cm) was clearly inferior for FDG-DHC-SPECT compared to conventional PET. The authors conclude that FDG-DHC-SPECT cannot be considered comparable to conventional PET for oncologic diagnosis. Other case series of FDG-DHC-SPECT report similar results, i.e., an inferior diagnostic performance of FDG-DHC-SPECT compared to PET, particularly for smaller lesions, or those located outside the lungs. ^7,8,9,10

Conclusion:
Regarding oncologic applications, the data suggest that FDG-SPECT cannot be considered an equivalent diagnostic modality compared to conventional PET scanning, particularly for small lesions. There are inadequate data regarding the diagnostic performance of FDG-SPECT compared to other anatomic imaging techniques, such as CT or MRI scan.

Cardiac Applications
Both FDG-collimated and FDG-DHC-SPECT have been studied as techniques to evaluate myocardial viability. Srinivasan and colleagues reported on a case series of 28 patients with chronic coronary artery disease and left ventricular dysfunction.¹¹ All patients underwent FDG-collimated-SPECT, conventional PET and thallium SPECT studies. Conventional PET served as the gold standard. The authors reported excellent overall correlation among all 3 techniques, although differences emerged on subset analysis. For example, for those with severe left ventricular dysfunction (i.e., ejection fraction < 25%), conventional thallium SPECT tended to underestimate myocardial viability compared to FDG-collimated-SPECT and conventional PET. However, the majority of discordant lesions were located in the inferior wall, and the poorer performance of SPECT in this region may not be related to any limitation in thallium delivery or uptake, but instead due to the physical property of attenuation of the lower energy photons (compared to FDG) as they traverse the thorax. This limitation in thallium SPECT scanning may be corrected by attenuation correction.¹² More recently, Hasegawa and colleagues compared FDG-DHC-SPECT, FDG-collimated SPECT and PET scanning as techniques to evaluate myocardial viability in 25 patients.¹³ The authors reported that the image quality of FDG-DHC-SPECT was superior to that of FDG-collimated SPECT, and equivalent to conventional PET if adequate attenuation correction is used.

Conclusion
The data suggest that all 4 methods — conventional thallium SPECT, FDG-collimated-SPECT, FDG-DHC-SPECT and PET scanning — may be clinically useful and considered equivalent in most cases. However, it is difficult to determine in which subsets of patients one technique may be superior to another, or if the diagnostic performance is improved with the combination of techniques. There are no data to suggest that the combination of FDG-SPECT with PET scans improves diagnostic performance of either technique alone. There are no data regarding the use of FDG-SPECT in the evaluation of coronary perfusion defects.

Neurologic Disorders
PET scans have been widely used in the evaluation of neurological disorders, ranging from epilepsy to dementias. There are inadequate data to compare FDG-SPECT to PET for neurological disorders.

References:

1. Martin WH, Delbeke D, Patton JA et al. Detection of malignancies with SPECT versus PET, with 2-[fluorine-18] fluoro-2-deoxy-D-glucose. Radiology 1996; 198(1):225-31.
2. Lonneux M, Delval D, Bausart R et al. Can dual-headed 18F-FDG SPET imaging reliably supersede PET in clinical oncology? A comparative study in lung and gastrointestinal tract cancer. Nucl Med Commun 1998; 19(11):1047-54.
3. Tatsumi M, Yutani K, Watanabe Y et al. Feasibility of fluorodeoxyglucose dual-head gamma camera coincidence imaging in the evaluation of lung cancer: comparison with FDG PET. J Nucl Med 1999; 40(4):566-73.
4. Weber W, Young C, Abdel-Dayem HM et al. Assessment of pulmonary lesions with 18F-fluorodeoxyglucose positron imaging using coincidence mode gamma cameras. J Nucl Med 1999; 40(4):574-8.
5. Delbeke D, Patton JA, Martin WH et al. FDG PET and dual-head gamma camera positron coincidence detection imaging of suspected malignancies and brain disorders. J Nucl Med 1999; 40(1):110-7.
6. Shreve PD, Steventon RS, Deters EC et al. Oncologic diagnosis with 2-[fluorine-18] fluoro-2-deoxy-D-glucose imaging: dual-head coincidence gamma camera versus positron emission tomographic scanner. Radiology 1998; 207(2):431-7.
7. Zimny M, Kaiser HJ, Cremerius U et al. Dual-head gamma camera 2-[fluorine-18]-fluoro-2-deoxy-D-glucose positron emission tomography in oncological patients: effects of non-uniform attenuation correction on lesion detection. Eur J Nucl Med 1999; 26(8):818-23.
8. Boren EL, Delbeke D, Patton JA et al. Comparison of FDG PET and positron coincidence detection imaging using a dual-head gamma camera with 5/8 inch NaI (T1) crystals in patients with suspected body malignancies. Eur J Nucl Med 1999; 26(4):379-87.
9. Weber WA, Neverve J, Sklarek J et al. Imaging of lung cancer with fluorine-18 fluorodeoxyglucose: comparison of a dual-head gamma camera in coincidence mode with a full-ring positron emission tomography system. Eur J Nucl Med 1999; 26(4):388-95.
10. Yutani K, Tatsumi M, Shiba E et al. Comparison of dual-head coincidence gamma camera FDG imaging with FDG PET in detection of breast cancer and axillary lymph node metastasis. J Nucl Med 1999; 40(6):1003-8.
11. Srinivasan G, Kitsiou AN, Bachrach SL et al. [18F] fluorodeoxyglucose single photon emission computed tomography: can it replace PET and thallium SPECT for the assessment of myocardial viability? Circulation 1998; 97(9):843-50.
12. Udelson JE. Steps forward in the assessment of myocardial viability in left ventricular dysfunction. Circulation 1998; 97(9):833-8.
13. Hasegawa S, Uehara T, Yamaguchi H et al. Validity of 18F-fluorodeoxyglucose imaging with a dual-head coincidence gamma camera for detection of myocardial viability. J Nucl Med 1999; 40(11):1884-92.
14. Medicare Decision Memorandum: Positron Emission Tomography Scanner Technology. 

Coding Section

Procedure and diagnosis codes on Medical Policy documents are included only as a general reference tool for each policy. They may not be all-inclusive.  

This medical policy was developed through consideration of peer-reviewed medical literature generally recognized by the relevant medical community, U.S. FDA approval status, nationally accepted standards of medical practice and accepted standards of medical practice in this community, Blue Cross Blue Shield Association technology assessment program (TEC) and other nonaffiliated technology evaluation centers, reference to federal regulations, other plan medical policies and accredited national guidelines.

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