WHAT IS PET/CT?
PET/CT provides the fusion of two powerful diagnostic imaging techniques in one machine. Positron Emission Tomography (PET) is an advanced molecular imaging procedure that provides a way to diagnose disease through the measurement of metabolic activity. PET is a functional imaging technique: the images are derived from the metabolism of radiopharmaceuticals absorbed by the tissue under study. Computed Tomography (CT) is an X-Ray method producing cross sectional imaging as well as other views of a patient’s anatomy. Using the two methods simultaneously allows for higher accuracy in image presentation.
PET/CT complements all other imaging modalities including routine X-ray, Ultrasound, MRI, and conventional CT; however PET/CT can often detect pathology before it becomes visible with conventional imaging modalities because metabolic changes usually precede anatomic ones.
PET is a nuclear medicine procedure. The patient is injected with a radiopharmaceutical which concentrates at the site of metabolic activity. A sophisticated detector images the distribution of the radiopharmaceutical in the body, thus imaging tissue function. PET can detect the spread of malignant tumors and differentiate cancerous tissue from benign tumors and scar tissue. When coupled with simultaneous CT providing high quality anatomic landmarks the PET/CT provides increased diagnostic accuracy. This can have a dramatic impact on patient diagnosis, patient treatment, and response to patient therapy, patient care planning and care.
HOW PET/CT WORKS
Radiopharmaceuticals based on positron emitting isotopes, such as fluorodeoxyglucose, become signal-emitting tracers when injected into the patient. For a PET/CT scan, patients are first injected with a radiopharmaceutical, usually FDG, a radioactive glucose compound. After the isotope uptake time, the patient is imaged on the CT portion of the PET/CT system creating the landmark images. With the isotope compounds distributed throughout the body and processed by the organ being targeted for imaging, the patient transits into the pet portion of the scanner and the PET scanner detects the FDG accumulated in glucose-avid organs or tissues and creates images that are displayed on a video monitor. The signals detected by both PET and CT are processed by a computer to create fused images that display on the monitor screen. The distribution of metabolic activity discretely landmarked by the CT anatomic images are presented as a set of tomographic slices. Because cancer cells usually have a higher metabolic rate than surrounding cells, they absorb more of the tracer and will show up more prominently on the image.
PET/CT’S ADVANTAGES FOR PATIENT DIAGNOSIS
PET/CT enables physicians to better determine the presence of a tumor, as well as the extent and spread of disease. With better information about the early presence or spread of cancer, physicians can select the treatment approach that’s most effective for the patient.
An important benefit of PET CT is its high-definition anatomically specific imaging which can detect tissue abnormalities even in the absence of structural changes. The detection of small amounts of malignant tissue, often undetectable by conventional imaging techniques, can have a major impact on the choice of treatment for patients, which may involve drug therapy, surgery, radiation, chemotherapy or a combination of all available options.
PET/CT AND CANCER
PET/CT is considered particularly effective in identifying whether or not cancers are responding to treatment, if a person is cancer free, or if a cancer has recurred—and where. Cancers for which PET/CT is considered particularly effective include: lung, lymphoma, melanoma, breast, colorectal, esophageal, head and neck, pancreatic, ovarian, cervical and thyroid. Cancer of the prostate, kidney and musculoskeletal system can be FDG avid and may be suitable for PET/CT scanning in select cases.
- Staging of Cancer: PET/CT is extremely sensitive in determining the full extent of disease, especially in the cancers noted above. Confirmation of metastatic disease allows the physician and patient to more accurately decide on how to proceed with the patient’s management.
- Checking for recurrences: PET/CT is currently considered to be the most accurate diagnostic procedure to differentiate tumor recurrences from radiation necrosis or post-surgical changes. Such an approach allows for the development of a more rational treatment plan for the patient.
- Assessing the Effectiveness of Chemotherapy: The level of tumor metabolism is compared on PET/CT scans taken before and after a chemotherapy cycle. A successful response seen on a PET/CT scan frequently precedes alterations in anatomy and is considered to be an earlier indicator of tumor shrinkage than might be seen with other diagnostic modalities.
- Early Detection: Since PET images biochemical activity, PET/CT can accurately characterize a tumor as benign or malignant, thereby avoiding surgical biopsy when the PET/CT scan is negative. Conversely, since a PET/CT scan images the entire body, confirmation of non-local metastasis can alter treatment plans in certain cases from surgical intervention to chemotherapy.
PET IN NEUROLOGY
- Epilepsy: PET/CT has helped advance the diagnosis of refractory epilepsy leading to cures in certain cases. PET is one of the most accurate methods available to localize the areas of the brain causing epileptic seizures and to determine if surgery is a viable treatment option.
- Dementia: The brain is highly dependent on glucose metabolism. PET/CT can reveal abnormal patterns of uptake in the brain and is, therefore, a valuable tool for assessing patients with various forms of dementia. It is particularly useful in diagnosing Alzheimer’s disease and in distinguishing Alzheimer’s disease from other dementia disorders, such as vascular dementia, Parkinson’s disease, Pick’s disease and Huntington’s disease.
- Alzheimer’s Disease: Although the only definitive test for Alzheimer’s disease (AD) is autopsy, PET/CT can supply important diagnostic information. When comparing a normal brain vs. an AD-affected brain on a PET/CT scan, a distinctive image appears in the AD-affected brain. This pattern may be seen very early in the course of Alzheimer’s disease, when other imaging is normal. The confirmation of AD is a long process of elimination that averages between two and three years of diagnostic and cognitive testing. PET/CT can help to shorten this process by identifying distinctive patterns earlier in the course of the disease. Since currently available medical treatments seem to be more effective if started early, a correct and early diagnosis may have important patient ramifications.
PET IN CARDIOLOGY
PET/CT has a number of important uses in cardiology. PET/CT can be particularly helpful in the diagnosis of CAD if conventional perfusion (nuclear cardiac stress test) or echocardographic stress tests are equivocal.
Myocardial viability offers the most important role for PET/CT in cardiology. PET/CT flow/metabolism studies are generally regarded as the “gold standard” in identifying hibernating myocardium, a critical element in determining successful functional recovery after revascularization.
PET/CT and CT or MRI:
PET/CT measures metabolism, unlike MR or CT, which “see” structure. It therefore complements these modalities, as it can often detect an active tumor before it can be seen on MR or CT. PET/CT can also often differentiate malignant from non-malignant masses such as scar tissue formed from surgery or radiation therapy. PET/CT is often used in conjunction with an MR through “fusion” to provide a full three-dimensional view of an organ and the location of cancer within that organ, by superimposing the functional and structural information for PET onto CT or MR.
Cost & Reimbursement:
Many private insurance companies reimburse for PET/CT scans. Medicare reimburses for PET/CT for the following cancers: breast, colorectal, lung, lymphoma, melanoma, head and neck and esophageal. Medicare also reimburses for myocardial viability and for refractory seizures (epilepsy). See the attached 2013 CMS approved procedures for reimbursement below. For the most accurate information, please contact your patient’s insurance carrier directly.
HOW TO PREPARE YOUR PATIENTS FOR A PET/CT SCAN
For most patients, the PET/CT scan takes about two hours to complete, depending on whether the whole body, or a particular part of the body is scanned.
On the day of the test, patients should bring:
- All previous studies, including CT and/or MR films and reports.
- Any prior PET or PET/CT images and reports if one was performed at some other time or site.
- Their chemotherapy history, including date of most recent treatment.
- Insurance information.
Restrictions and Preparing for the Test:
- Patients should not eat or drink (other than water) 6 hours prior to the exam.
- Patients are encouraged to drink plenty of water prior to the exam.
- Patients should refrain from strenuous excise for 2 days prior to the exam.
- Diabetic patients require special preparation and should call the PET/CT Center for instructions
Medicare Indications for PET Scans:
A list of specific indications, including those currently reimbursed by Medicare.
Effective for dates of service on or after June 11, 2013, this is a summary of FDG PET coverage for oncologic diagnoses.
FDG PET for Solid Tumors and Myeloma
Initial Treatment Strategy (formerly “diagnosis” & “staging”)
Subsequent Treatment Strategy (formerly “restaging” and “monitoring response to treatment”)
|Head and Neck (not thyroid or CNS)||Cover||Cover|
|Non-small cell lung||Cover||Cover|
|Cervix||Cover with exceptions *||Cover|
|Small cell lung||Cover||Cover|
|Soft tissue sarcoma||Cover||Cover|
|Breast (male and female)||Cover with exceptions *||Cover|
|Melanoma||Cover with exceptions *||Cover|
|All other solid tumors||Cover||Cover|
|All other cancers not listed||Cover||Cover|
*Cervix: Nationally non-covered for the initial diagnosis of cervical cancer related to initial anti-tumor treatment strategy. All other indications for initial anti-tumor treatment strategy for cervical cancer are nationally covered.
*Breast: Nationally non-covered for initial diagnosis and/or staging of axillary lymph nodes. Nationally covered for initial staging of metastatic disease. All other indications for initial anti-tumor treatment
*Melanoma: Nationally non-covered for initial staging of regional lymph nodes. All other indications for initial anti-tumor treatment strategy for melanoma are nationally covered.
Decision Memo for Positron Emission Tomography (FDG) for Solid Tumors (CAG-00181R4) – http://www.cms.gov/medicare-coverage-database/details/nca-decision-memo.aspx?NCAId=263
A. The Centers for Medicare & Medicaid Services (CMS) has determined to end the requirement for coverage with evidence development (CED) under §1862(a)(1)(E) of the Social Security Act (the “Act’) for 18F fluorodeoxyglucose positron emission tomography (FDG PET) for oncologic indications which are contained in section 220.6.17 of the Medicare National Coverage Determinations Manual. This removes the requirement for prospective data collection by the National Oncologic PET Registry (NOPR) for those cancers or cancer types that had been covered under CED (as listed in Appendix A).
B. CMS has determined that three FDG PET scans are covered under § 1862(a)(1)(A) when used to guide subsequent management of anti-tumor treatment strategy after completion of initial anticancer therapy. Coverage of any additional FDG PET scans (that is, beyond three) used to guide subsequent management of anti-tumor treatment strategy after completion of initial anti-tumor therapy will be determined by local Medicare Administrative Contractors.
As reflected in the proposed decision memorandum (PDM), CMS found little evidence about effects of FDG PET on outcomes for patients whose initial therapy for prostate cancer had been completed. Current literature on PET tracers for recurrence or tumor response seemed to focus mainly on a different radiopharmaceutical, 11C choline.
However, public comments about the PDM indicated that evidence of the value of FDG PET scans was in some cases provided in therapeutic studies and was also available in more recent articles. After review of these important components of the evidence base, CMS agrees that a significant benefit of FDG PET scans is their use to determine effect of treatment, especially at certain types of progressive prostate disease.
As examples of the importance of this, NOPR findings (e.g., Hillner 2012) indicate that in about 40% of instances, physicians would change their intended therapy for patients with prostate cancer. Despite the known concerns about lack of glucose avidity of prostate cancer cells, as mentioned in Hillner 2009 other studies indicated that FDG PET CT could be valuable even for assessing activity of bone metastases of prostate cancers in a large majority of patients (Meirelles 2010).
Nevertheless, we are convinced that FDG PET/CT imaging’s selective use in assessing progression of prostate cancer does provide valuable additional information for managing treatment decisions, and therefore we consider its use for subsequent treatment strategy planning to be reasonable and necessary. We note that in many of these studies, a rising PSA level was key to the clinical suspicion of progressive or recurrent prostate cancer.
We also agree with the NOPR public comments emphasizing that physicians were found to selectively employ FDG PET for subsequent anticancer treatment planning in appropriate patients. We expect that post-coverage analysis (PCA) review by CMS will confirm this NOPR observation.
Consequently, CMS proposes that use of FDG PET/CT when used to guide subsequent anti-tumor treatment strategy for patients with cancer of the prostate is reasonable and necessary under § 1862(a)(1)(A).