Emerging role of PET in the diagnosis and staging of lung cancer

Efficacy of Tc-99m depreotide scintigraphy in the evaluation of solitary pulmonary nodules

PURPOSE

Tc-99m depreotide is a peptide analogue of a somatostatin receptor that preferentially binds to somatostatin receptors 2, 3, and 5. Many lung tumors may express these receptors to a greater extent than normal tissue. Tc 99m depreotide study is a noninvasive, receptor-specific imaging agent that is used to assess malignant versus benign single pulmonary nodules before biopsy.

MATERIALS AND METHODS

Thirty-nine consecutive patients (15 men, 24 women), with mean age 56.6 years (range 39-86) underwent 42 studies. The single-photon emission computed tomographic scan of the chest and whole-body imaging were performed 2 hours after intravenous injection of Tc 99m depreotide (average dose, 24 mCi). The region of interest was drawn around each lesion, and the tumor-to-background ratio was measured. Images were classified as true positive when the tumor uptake and histopathology were concordant. The results were classified as true negative when there was no uptake in the absence of malignancy. The results were classified as false positive when there was uptake in areas other than tumor and were false negative when no uptake in the tumor was identified. The computed tomographic and pathological correlations were performed.

RESULTS

The comparison of technetium Tc 99m depreotide imaging with computed tomographic study revealed a sensitivity of 1.0 versus 0.9, a specificity 0.43 versus 0.19, accuracy 0.71 versus 0.55, positive predictive value 0.64 versus 0.53, and negative predictive value 1.0 versus 0.67,. The tumor-to-background ratio ranged from 1.15 to 3.77. There was no relationship between the histology and the intensity of tumor uptake. The tumor uptake was high in sites of acute and active inflammation.

CONCLUSION

Technetium Tc 99m depreotide imaging is a sensitive imaging modality with better specificity and negative predictive value than computed tomography. There is no relationship between tumor uptake and differentiation of the tumor. We recommend a technetium Tc 99m depreotide study forthe evaluation of solitary pulmonary nodules, especially when positron emission tomography is not available before biopsy.

Value of positron emission tomography for lung cancer staging

OBJECTIVE

The therapeutic strategy in non-small-cell lung cancer (NSCLC) requires exact staging of tumour invasion (T) as well as differentiation between ipsi- and contralateral lymph node invasion (N1/2 vs N3). [18F]FDG-positron emission tomography (FDG-PET) has been shown to detect invaded N with high accuracy while correct determination of T appears to be unclear. The purpose of this prospective study was to evaluate benefit and necessity of 18FDG-PET as an additive to conventional staging modalities.

METHODS

Forty patients with suspected non-small-cell lung cancer (NSCLC) were staged by means of computed tomography (CT), bronchoscopy, mediastinoscopy and bone scintigraphy. Additionally, attenuation corrected FDG-PET of the thorax was performed pre-operatively for analysis of T and N topography. After surgical resection with radical lymphadenectomy T and N staging results of CT and PET were compared with the pathological diagnoses. Specificity, sensitivity, positive predictive value and accuracy of CT and PET were calculated.

RESULTS

Twenty three squamous cell carcinomas, 14 adenocarcinomas, and three non-malignant tumours were found. Accuracy of CT-T was 0.75 and of PET-T 0.78; accuracy of CT-N was 0.78 and of PET-N 0.80. By combination of CT-T and PET-T accuracy was 0.88. Combination of CT-N and PET-N yielded an accuracy of 0.90. In two out of three cases, PET correctly determined T0. In two cases non-malignant inflammatory lymph nodes were falsely staged as malignant by PET.

CONCLUSIONS

Adequate pre-operative T- and N-staging is possible with both CT and FDG-PET. Accuracy can be improved by combination of CT and FDG-PET. FDG-PET is superior to CT in order to differentiate between malignant and benign tumours. However, acute inflammation can mimic malignant lymph node invasion. FDG-PET is justified as a supporting staging measure in cases presenting unclear differentiation between N2 and N3 after conventional staging and is helpful in cases with unclear cell type of the primary tumour.

Positron emission tomography (PET) of non-small cell lung cancer

Positron emission tomography (PET) with FDG has shown to be of substantial value in differential diagnosis of pulmonary lesions and in the assessment of lymph node involvement with higher sensitivity and specificity than CT. A negative PET scan of the mediastinum suggests that mediastinoscopy is unnecessary and that these patients can proceed directly to thoracotomy. The method is also useful for the visualization of distant metastases. Since changes of treatment may result after identification of distant metastases PET is also cost-effective [Eur J Nucl Med 27(2000)1598; Australas Radiol 45(2001)9]. Furthermore, changes of tumor metabolism can be detected with PET at early stages after treatment, which can be used for therapy monitoring and for the detection of recurrent tumor tissue after completion of treatment.

Imaging of lung cancer with CT, MRT and PET

The staging of non-small lung cancer has to be performed in an interdisciplinary approach considering all clinical, radiological and histologic results. The staging using imaging procedures is done according to the TNM classification with T describing the extent of the primary tumor, N the presence and location of metastatic lymph nodes and M the presence or absence of distant metastases. It is important to remember that the individual stages of the TNM classification have undergone numerous revisions and thus need to be considered in their most recent version [Chest 111 (1997) 1718; Chest 111 (1997) 1710]. Noninvasive information about the stage of the disease is important for the planning and optimization of therapy. This may be done with imaging procedures such as, CT, MRT or PET.

Image-Guided Fine Needle Aspiration Strategies for Staging of Lung Cancer

Image-guided transthoracic, bronchoscopic, and endoscopic ultrasound fine needle aspiration (FNA) greatly facilitates lung cancer staging by having the potential to precisely biopsy lung lesions and virtually all mediastinal lymph node stations. Imaging modalities alone, including chest x-ray, computed tomography (CT), magnetic resonance imaging, and positron emission tomography identify lesions suspicious for cancer but cannot make a tissue diagnosis. We describe an algorithm for the diagnosis and tumor-node-metastasis staging of lung cancer that uses procedures with the least invasiveness and cost with the highest diagnostic yields. For the anterior mediastinum, fluoroscopic-, ultrasound-, or CT-guided transthoracic FNA (which has a greater yield than bronchoscopy and is less invasive than mediastinoscopy) should be the primary technique for lymph node sampling. In the middle mediastinum, CT-guided transthoracic FNA is preferred for all nodal stations except subcarinal. Endoscopic ultrasound-guided FNA (EUS-FNA), which enables real-time biopsies within 5 cm of the esophagus, is preferred for sampling subcarinal and posterior mediastinal nodes because the yield is similar to CT-guided transthoracic FNA, with minimal risk of pneumothorax. The posterior mediastinum is also accessed by fluoroscopic- or CT-guided transthoracic FNA or video-assisted thoracic surgery. Sampling of the aorticopulmonary window depends on lymph node size; if the nodes are large enough to displace the aortic arch and pulmonary vein, then EUS-FNA is attempted, and if the nodes are not sufficiently enlarged, CT-guided transthoracic FNA should be performed prior to thoracoscopy or thoracotomy.

Developments in imaging. An historical review

Following the discovery of X-rays by Roentgen in 1895, it was 70 years later that the specialty of imaging really took off, with ultrasound, CT, Nuclear medicine, and MRI now an integral part of all large departments. The recent progress has been accelerated by advances in computer technology which aided the development of imaging techniques that do not use ionising radiation. Some imaging techniques are replacing other more hazardous diagnostic procedures, (e.g. MRCP v ERCP, and MRA v catheter angiography) while some are able to provide almost perfect anatomical detail e.g. brain MRI. Techniques using radioisotopes provide more functional information which can be used to complement the morphological studies. We have witnessed the birth and maturation of Interventional Radiology. This is a highly skilled subspecialty enabling some surgical procedures to be replaced by minimally invasive methods using image guidance. These range from simple drainage procedures and guided biopsies to complex aortic bifurcation stent graft insertions. The potential for digital storage of all images is already established and the filmless radiology department in the more developed countries could be the norm by 2020.

Positron emission tomography in initial staging and diagnosis of persistent or recurrent disease

Positron emission tomography (PET) constitutes a major advance in the diagnosis, staging, prognostic assessment, and follow-up of lung cancer. However, it is not a magic bullet that can solve all of the uncertainties that beguile the imaging of this disease. Small lesions, particularly those in the brain, may often be missed with PET, and three-dimensional localization of suspected sites may also be unreliable. We are still learning how best to apply this new technology in an environment that demands the efficient use of medical resources. PET will probably be used most enthusiastically in the prethoracotomy staging of patients who are considered operable or probably operable on the basis of computed tomography and in the assessment of treatment response and disease recurrence when clinical management will be determined by prompt recognition of these events.