Medical Radiography Program - PET Imaging and Oncology

Medical Radiography Program Objectives

  • Discuss the principles of PET/CT FDG oncology imaging.

  • State the principal reasons for the growth of PET oncology imaging.

  • Recognize the normal biodistribution of FDG, and list those organs with intense, moderate, or mild FDG activity.

  • Compare the various patterns of normal FDG myocardial activity.

  • Discuss the normal patterns of head and neck FDG activity.

  • Discuss benign causes of increased FDG activity.

  • Describe the variations in FDG biodistribution caused by improper patient preparation.

  • Recite the steps in properly preparing a patient for an FDG PET scan.

Introduction to Positron Emission Tomography (PET)

  • General Overview:

    • PET imaging in oncology is a rapidly emerging tool with increasing availability.

    • It represents one of the most effective diagnostic tools in nuclear medicine.

  • Historical Background:

    • In the late 1980s, PET began showing effectiveness in cancer imaging; reimbursement and cost were significant obstacles to widespread use.

    • In 1998, the Centers for Medicare and Medicaid Services (CMS) began to reimburse for FDG PET scans for specific conditions, such as solitary pulmonary nodules and non-small-cell lung carcinoma.

  • Impact on Practice:

    • The breakthrough in reimbursement led to expanded coverage for other cancers where PET was shown to be the most accurate imaging technique for identifying and staging diseases.

    • Payer reimbursement significantly drove the rapid growth of PET facilities for patients and their referring physicians.

Intracellular 18F-FDG Metabolism

  • Radiopharmaceutical:

    • The most commonly used radiopharmaceutical in PET cancer imaging is 2−[18F]−fluoro−2−deoxy−D−glucose2- [18F]-fluoro-2-deoxy-D-glucose (18F-FDG).

    • Structurally, 18F-FDG is a nonphysiological compound similar to glucose.

    • Acts as an external marker for cellular glucose metabolism.

  • Glucose Metabolism in Cancer:

    • Cancer cells utilize glucose at significantly higher rates than normal cells, increasing glucose flow into cancerous cells.

    • Higher activity of hexokinase, the first enzyme in glucose breakdown, in cancerous cells results in increased visualization of malignant tumors noninvasively.

  • Variability:

    • Intracellular FDG activity varies among different types of cancer.

    • Challenges:

    • Conditions like infection, inflammation, and others can also increase FDG use, complicating diagnosis.

    • Some cancers may use FDG at rates similar to normal tissues, remaining undetectable.

Patient Preparation and Injection for FDG PET Scans

  • Preliminary Recommendations:

    • Avoid strenuous exercise for at least 24 hours before the scan.

    • A high-protein, restricted carbohydrate diet may be recommended before fasting.

    • Patients should remain well hydrated prior to the procedure.

    • A fasting period of 4 to 6 hours is required before injection.

  • Medication Guidelines:

    • Patients can take regular medications unless contraindicated.

    • Breast-feeding mothers should pump milk to sustain their infants for about one day before radiopharmaceutical administration.

  • Records and Comfort:

    • Record height, weight, and fasting blood glucose before FDG administration.

    • Patients should rest quietly, with warm blankets provided for comfort during localization (60 to 90 minutes).

    • Ensure the patient voids completely just before imaging.

  • Optional Practices:

    • Anxiolytics, diuretics, bowel preparations, and urinary catheters are optional based on practice decisions.

Overview of Diabetic Patient Preparation

  • Consultation Prior to Appointment:

    • Discuss disease management regarding diabetes, including control mechanisms (diet, insulin, oral hypoglycemics).

    • Direct questions about the patient's fasting blood glucose measurements and journaling of glucose trends.

  • Scheduling Considerations:

    • Type I/insulin-dependent patients should be scheduled early, fasting without unnecessary insulin.

    • Type II/non-insulin dependent patients may have appointments later to accommodate a light breakfast before fasting.

  • Medication and Monitoring:

    • Patients must bring medications for diabetes management to the appointment, followed by medication reconciliation.

    • Monitor signs of hypoglycemia and establish policies for managing extreme blood glucose levels.

PET Scan Acquisition

  • Scan Types:

    • Methods include limited-area scanning, dynamic imaging, whole-body imaging (base of skull to mid-thigh), or total-body imaging.

    • Most oncology patients receive scans from base of skull to mid-thigh, with limited-area scanning reserved for specific needs.

    • Dynamic imaging only used when the precise lesion is known.

    • Total-body scans are frequently used for malignant melanomas or sarcomas.

  • Patient Positioning:

    • Ensure patients void prior to the procedure and remove potential image artifacts (e.g. metallic objects).

    • Use a recumbent position with support for comfort and steady arms.

    • For head and neck cancers, a head holder with chin restraint is utilized to minimize motion.

    • Continuous patient evaluation throughout the procedure is necessary.

Normal Whole-Body FDG Distribution

  • Evaluation Requirements:

    • Understanding normal anatomy and biodistribution of FDG is crucial for identifying pathological accumulations.

  • Common Sites of FDG Activity:

    • Intense FDG Activity: Brain.

    • Moderate FDG Activity: Liver, kidneys (especially the calyces and pelves).

    • Mild FDG Activity: Bladder.

  • Variable Activity Sites:

    • Includes salivary glands, thyroid, heart, thymus (children), spleen, esophageal ampulla, stomach, bowel (especially colon), endometrium (during menses), bone marrow, muscles, and testicles.

Normal Variations in FDG Localization

  • Variability of Normal Patterns:

    • Not all variations can be detailed; patient history and correlated imaging studies are essential for identifying deviations from normal.

    • Notable Variations: Myocardial activity, thyroid, mouth, salivary glands, extraocular muscles, and small bowel activity variation.

  • Diagnostic Frustrations:

    • Potential misdiagnoses can arise due to increased activity in:

    • Muscular or brown fat in neck and shoulders (trapezius, sternocleidomastoid, subclavius).

    • Gastrointestinal tract, particularly the colon activity.

    • Other sources of activity include surgical sites, ostomy sites, recovering bone marrow, arthritic joints, infections, inflammations, pleural effusions, biopsies, or injection sites.

Applications of PET in Oncology

  • Indications for FDG PET Oncology Studies: Important to note primary indications across various cancers such as solitary pulmonary nodules, non-small-cell lung carcinoma, lymphoma, melanoma, and more.

  • Solitary Pulmonary Nodule (SPN):

    • High-risk patients (e.g., smokers) are often screened for SPNs using CT and chest radiographs which may outline benign or malignant nodules.

    • Increased FDG uptake in SPNs indicates potential malignancy while absence is more indicative of benignity, although low-grade cancers may still show minimal uptake.

  • Non-Small-Cell Lung Carcinoma (NSCLC):

    • FDG PET shows superiority to CT and MRI for locating lymph node involvement and distant metastases, especially in adrenal glands, allowing better staging and treatment options.

  • Small Cell Lung Carcinoma (SCLC):

    • Represents about 15% to 20% of lung cancers, known for rapid progression and higher occurrence in women.

  • Melanoma:

    • Incidence has doubled in the last 30 years, effectively utilizing FDG for total-body PET scans which improve metastatic assessments compared to conventional techniques.

  • Lymphoma:

    • Classification into Hodgkin disease and Non-Hodgkin lymphoma (more common).

    • Lymphomas typically show high FDG accumulation; crucial for staging and monitoring treatment response.

  • Myeloma:

    • Initiates in the bone marrow with classification depending on whether it presents as a single mass (plasmacytoma) or multiple (multiple myeloma).

    • PET plays a significant role in staging and disease extent evaluation.

  • Colorectal Cancer:

    • The fourth most common cancer, FDG PET proves more accurate than CT in assessing tumor involvement, beneficial in surgical candidate selection.

  • Head and Neck Cancer:

    • Nearly all case present as squamous cell carcinomas, for which FDG PET is effective in detecting occurrences and recurrences.

  • Esophageal Cancer:

    • Typically diagnosed late, with poor survival rates; PET imaging approval by CMS in 2001.

  • Breast Cancer:

    • Leading cancer in women; critical for detecting lymph node metastases and for evaluating treatment responses.

  • Brain Cancer:

    • Generally secondary tumors; FDG PET acts as an adjunct tool for differentiating tumors from traditional necrosis.

  • Prostate Cancer:

    • Most frequently diagnosed cancer in men post skin cancers; current technology limitations necessitate future advancements in PET imaging solutions.

  • Cervical Cancer:

    • Useful for initial staging, with limited data on recurrent management management effectiveness.

  • Ovarian Cancer:

    • High FDG uptake offers PET a role in screening and managing responses to therapy.

  • Testicular Cancer:

    • Divided into seminomas and nonseminomas, with significant uptake in PET imaging, except for mature teratomas.

  • Thyroid Cancer:

    • FDG PET is a capable diagnostic approach for poorly differentiated cancers despite challenges with normal FDG variations.

  • Types of Thyroid Cancer (Papillary, Follicular, Medullary, Anaplastic):

    • Common forms include papillary and follicular; early detection aligns with successful treatment outcomes.

  • Pancreatic Cancer:

    • Silent killer with a very low 5-year survival rate; PET assists in differentiating chronic masses and assessing metastasis, with limitations on acute inflammation imaging.

  • Gastric Cancer:

    • Most commonly adenocarcinomas, with PET imaging added value in treatment response appraisal.

  • Hepatocellular Carcinoma:

    • Reflects primary liver cancers; metastases to liver from other impacts may also require assessment.

  • Endometrial Cancer:

    • The most prevalent female gynecological cancer; PET aids in staging and metastatic involvement evaluation.

  • Sarcomas:

    • Malignancies key to connective tissues, with PET providing valuable insights in clinical management.

  • Leukemia:

    • Blood-originating cancer classified based on implicated cell types; PET is approved for usage in liquid tumors.

  • Unknown Primary Tumors:

    • Gene profiling has become essential for management and diagnosis in malignancies without identifiable primary sites.

Future Trends in PET Imaging

  • Instrumentation and Algorithms:

    • Continuous evolution of instrumentation and development of more sophisticated and reliable processing algorithms.

  • Radiochemistry:

    • Improvements in stability and reproducibility of radiochemistry processes.

  • Emerging Technologies:

    • Advances in targeted gene therapies and monitored gene expression as forward-looking opportunities.

  • Accessibility and Affordability:

    • Increasing availability of radiopharmaceuticals for functional imaging enhancements.

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