Pet scan in chest
- 1. PET SCAN IN CHEST Dr Dileep MD Asst. Professor Pulmonary Medicine Mediciti Medical College Hyderabad
- 2. • What is a PET Scan? • Principle of PET Scan • What is PET-CT? • How to perform a PET Study? • Role of PET Scan in Pulmonology
- 3. What is a PET scan? • Positron Emission Tomography (PET) is a noninvasive, painless molecular imaging technology that allows to determine how organs inside the body are functioning on a cellular and molecular level • PET provides functional images of metabolic or physiologic processes
- 4. Principle of PET Scan • PET detects hypermetabolism in cells as a proxy for the presence of cancer • Tracer, 18-FluroDeoxyGlucose is a radio-labeled glucose analog that is selectively taken up by metabolically active cells • Mechanism of cellular uptake and initial phosphorylation of 18- FDG is similar to that of glucose • Once 18-FDG is phosphorylated (to FDG-6-phosphate) it cannot pass through complete glycolytic cycle, and it is trapped within cell
- 5. • The amount of intracellular 18- FDG is proportional to glucose uptake and, therefore, to the metabolic activity of the tissue • Malignant cells have increased glucose transport and metabolism due to accelerated cell proliferation and increased hexokinase activity
- 6. •The trapped 18-FDG undergoes radioactive decay by releasing a positron, which subsequently collides with an electron to produce two high-energy photons in a so-called Annihilation reaction •The photons travel in opposite directions and are detected by a ring scanner and are processed by computer into image
- 8. Integrated PET and CT (PET/CT) • PET and CT scans are now often done at the same time • Doing both scans at the same time gives anatomic detail as well as physiologic information • PET-CT is helpful in planning radiation therapy for patients with lung cancer associated with atelectasis
- 9. • Exact localization of a solitary metastatic lymphnode in the hilum (and, hence, classification as N1 or N2 disease) can be accomplished • In active granulomatous disease, such as tuberculosis, fungal lesions, pattern recognition on PET-CT, may improve characterization of the lesions • PET-CT increases the accuracy of malignant pleural mesothelioma staging and in determining appropriate therapy in patients being considered for extrapleural pneumonectomy
- 12. Performing a PET Study • Patient preparation: > 4 h fast, drink (but no sugar) • Blood sample for glucose(no hyperglycaemia) • 400 MBq of 18- FDG i.v., rest ½-1 hr • Scan time: – Regional Scan - 15-30 min – Whole body scan - 60 min
- 13. • “Standardized uptake value” (SUV),is a semiquantitative expression of the intensity of lesion by 18-FDG accumulation determined on PET scan • The SUV of an area is calculated as the amount of tracer in the tissue (microcuries per gram) divided by the amount of radiotracer injected (millicuries) divided by the patient’s body weight (kilograms). SUV= FDG Conc.in tissue dose injected / Bd wt. • An SUV >2.5 is considered suspicious for malignancy
- 14. PET IN Pulmonology Important indications in Pulmonology include • Lung Cancer • Mesothelioma
- 15. Role in Lung Cancer • Characterization of pulmonary nodules • Staging the mediastinum and identification of occult distant metastasis • Planning Radiotherapy • Monitoring for recurrence after completion of treatment
- 16. Solitary Pulmonary Nodule • SPN is defined as a single discrete pulmonary opacity that is surrounded by normal lung tissue that is not associated with adenopathy ,effusion or atelectasis and is commonly identified on chest radiographs and CT scans • PET provides an accurate, non-invasive diagnostic assessment of SPNs without the morbidity and costs associated with invasive tissue sampling
- 17. • Patients with positive PET scan requires further attention, as these lesions are considered malignant until proven otherwise • Lesions that do not have increased FDG uptake are usually benign. These patients can be followed with sequential imaging • Sensitivity and specificity of FDG-PET in detecting benign and malignant pulmonary nodules range from 92 to 98 percent and 79 to 100 percent, respectively
- 18. (A) Transaxial CT and fused FDG PET/CT image showing a solitary pulmonary nodule with spiculated borders in right lower lobe. Hypermetabolism is present within this nodule. Findings consistent with malignancy. (B) Solitary pulmonary nodule in a different patient in the right upper lobe. No hypermetabolism is present within this nodule. Findings consistent with a benign nodule.
- 19. • False-positive studies are seen with active inflammation due to aspergillosis, tuberculosis, or sarcoidosis • False-negative results are unusual ,but may be seen with malignancies which have a low metabolic activity e.g., bronchoaveolar carcinoma , carcinoid tumors or tumours < 8 mm in diameter
- 21. PET imaging is probably not indicated, in (1) Patients with symptoms, signs, or imaging characteristics that suggest infection (2) Patients with larger (>3cm) pulmonary mass lesions (of which 90% are malignant) (3) Patients with small pulmonary nodules that measure less than 7 to 8 mm in diameter (4) Patients with nodular GGOs (5) Patients who are not candidates for curative treatment
- 22. Staging of Lung Cancer • Once a diagnosis of lung cancer has been made, accurate staging is essential • Goal of radiologic studies is to distinguish those in whom tumor is resectable (stages I to IIIA) from those in whom tumor is not resectable (stages IIIB and IV) • In patients with known NSCLC, the results of staging both within and outside the thorax are key in determining operability
- 23. • The negative predictive value of 18FDG-PET is sufficiently high that a negative mediastinum on PET may preclude mediastinoscopy, and a positive mediastinum on PET should be further assessed to exclude false positive results • The average sensitivity and specificity for PET are 84 and 89 percent, respectively • PET is useful in identifying optimal site for mediastinal lymph node biopsy and selection of additional invasive methods for sampling lymph nodes inaccessible by mediastinoscopy
- 24. • Although CT, and occasionally MRI, is used to evaluate hilar and mediastinal nodes, the accuracy of detecting nodal metastases is approximately 60%. • Normal-sized lymph nodes may harbor malignant cells, and enlarged nodes may be benign • PET is more sensitive and specific than CT alone, with accuracy reported to be greater than 80%
- 25. FDG PET for extrathoracic metastasis • 40% with NSCLC have distant metastases at presentation, most often in the adrenal glands, bones, liver, or brain • Adrenal glands: PET has high sensitivity (>92%) and specificity (80%– 100%) • Bone: PET good sensitivity (90%), but higher specificity (98%) and accuracy (96%). • PET can detect bone metastases before reactive bone formation takes place or prior to development of gross anatomic abnormalities
- 27. Planning Radiotherapy • Planning for radiation treatment uses conventional imaging, including chest x-ray, CT, or MRI for anatomic extent of tumor • The use of anatomic imaging alone leads to inadequate radiation coverage and a higher chance of local recurrence • PET/CT guided RT improves radiation dose to the tumor and metastases and reduces dose to adjacent normal tissue • Thus, for radiation planning, integrating CT-PET appears to be more accurate than CT alone in defining tumor extent.
- 28. Representative PET/CT images from patient with lung cancer associated with atelectasis in which computed tomography cannot delineate the exact localization of the tumor. (A) A 60-year-old man with left lung adenocarcinoma limited to the perihilar region causing distal normometabolic atelectasis
- 29. PET/CT guided RT improves radiation dose to the tumor and metastases and reduces dose to adjacent normal tissue
- 30. Post treatment Follow-up • In patients with residual parenchymal abnormalities following radiotherapy, PET-scan can be used to distinguish between persistent or recurrent cancer and radiation fibrosis • PET is more sensitive in measuring the effects of anticancer therapy and it can be used for early response assessment • PET has a role in restaging after induction therapy in multimodality approaches for locally advanced lung cancer
- 32. This is a baseline PET/CTscan of a 51 year-old woman diagnosed with NSCLC showing a mass in the right lung, lymph nodes enlargement, and multiple pulmonary and bone metastases. After only 1 month of treatment with gefitinib, the PET/CT scan revealed an important metabolic response.
- 33. • In patients treated for lung cancer, PET offers prognostic value that correlates strongly with survival rate • Patients with positive PET results have a significantly worse prognosis than those with negative results • Lack of clearance of mediastinal lymph nodes or unchanged FDG uptake in the primary tumour usually denotes a poor outcome
- 34. Mesothelioma • PET can differentiate between benign and malignant mesothelioma • FDG-PET has a sensitivity of 91 % and specificity of 100 % and has excellent correlation with thoracoscopic findings • FDG-PET is also useful in identifying the -extent of disease locally and in the mediastinum, -evaluating abnormal findings in the contralateral lung, and -detecting occult extrathoracic metastases
- 35. • Pleuritis may produce a false-positive response on PET • Mesothelioma tends to have low FDG uptake in early stage of disease • PET also provides a semiquantitative index of disease activity that may be used to monitor the response to therapies • Patients with highly active FDG uptake have a poor long- term prognosis
- 37. Increased FDG-PET uptake in some benign pulmonary conditions • Infections – Lung abscess – Tuberculosis (and M avium intracellulare) – Bacterial pneumonia, Actinomycosis, Histoplasmosis, Invasive aspergillosis, aspergilloma, blastomycosis • Inflammatory lesions – Sarcoidosis – Vasculitis: Wegeners granulomatosis, takayasu arteritis, etc – Pneumoconiosis (silicosis, coal workers-, fibrosis)
- 38. Increased FDG-PET in some benign mediastinal adenopathies • Inflammation – Sarcoidosis – Anthrasilicosis • Infections – Histoplasmosis, – Tuberculosis (and M avium intracellulare) – Actinomycosis
- 39. Thank You