The role of nuclear medicine in pulmonary neoplastic processes.

It has been demonstrated that the single most important factor in determining survival in patients with bronchogenic carcinoma is the extent of spread of metastasis from the primary lesion. This explains the extensive efforts in developing accurate staging tests for pulmonary tumors, both primary and metastatic, with special emphasis on the determination of pulmonary hilar and mediastinal spread of disease. Continued improvements in nuclear medicine instrumentation along with the development of tumor specific radiopharmaceuticals, as well as agents that have the capability of tracking tumor viability, have changed the orientation of scintigraphic techniques in the evaluation of pulmonary neoplastic processes. Gallium scintigraphy is no longer considered as a primary imaging modality in the staging of pulmonary tumors, and in most institutions has been replaced by computed tomography (CT) for this purpose. It has been demonstrated that gallium, relative to other imaging modalities, is a sensitive indicator of hilar spread of tumor. However, because of the normally high background activity within the sternum and spine, mediastinal abnormalities are poorly detected. Since most pulmonary tumors metastasize via regional nodes to the pulmonary hilum and then to the mediastinum, the high sensitivity for the detection of pulmonary hilar abnormalities and the high specificity for mediastinal lesion detection suggest that gallium scintigraphy is a valuable adjunctive test when used appropriately. Thallium 201 as a tumor agent is being studied by several institutions. Preliminary results indicate a high degree of sensitivity for the detection of pulmonary hilar and mediastinal lesions and there are early indications that thallium is a promising agent to evaluate tumor viability. With the development of new generation monoclonal antibodies, the prospects for highly sensitive and specific agents for detecting hilar and mediastinal spread of tumor is extremely encouraging. CT and NMR have made major contributions to the noninvasive workup of patients with bronchogenic carcinoma. Neither modality has been demonstrated to be accurate enough to adequately evaluate this patient population. Thus, there is a critical need for new noninvasive tests that will accurately assess the status of the patient so that appropriate therapy can be instituted.