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BS, bone scan; CI, conventional imaging.

was 91% accurate and conventional imaging was 80%. FDG PET also was superior to bone scintigraphy for evaluating osseous metastases from lung cancer: sensitivity, specificity, PPV, and NPV for FDG-PET were 92%, 99%, 92%, and 99%, respectively, and for bone scintigraphy these were 50%, 92%, 50%, and 92%.

Erasmus et al.130 showed that FDG-PET was very sensitive and specific for evaluating adrenal metastases.

Metastatic disease to regional lymph nodes is categorized by location in relationship to the tumor. For N0 disease, the 5-year survival is 60%, for N2 it is 20%, and for N3 it is very poor.106

The "gold standard" method for mediastinal lymph node staging is supposed to be mediastinoscopy. The overall sensitivity of the "gold standard" is approximately 90%, and it has the disadvantage of sampling errors and the technical difficulty of obtaining overall coverage with a single entry port (i.e., inaccessibility in the aortopulmonary window lymph nodes).124

On the other hand, CT uses size criteria to assess nodal metastases (1 cm in the short axis dimension). The limitation of this approach is that enlarged nodes may reflect inflammatory changes rather than metastatic involvement and small nodes may contain tumor deposits. Dwamena et al.,131 in a meta-analysis of 514 patients, reported that the sensitivity, specificity, and accuracy of FDG-PET were 79%, 91%, and 92%, respectively, and those of CT were 60%, 77%, and 75%. The average sensitivity of PET for nodal disease from a variety of studies132-135 was 88% as compared with 63% for CT, and the average specificity was 91% for PET and 76% for CT.

The most common sites of metastases from lung carcinoma include lung (additional pulmonary lobes or to the contralateral lung), brain, adrenals, bone, and, less commonly, in liver and soft tissue.

Monitoring Therapy and Detection of Residual or Recurrent Disease

FDG-PET provides metabolic rather than anatomic information and allows functional assessment of lung tumors during or shortly after therapy. Patients with a complete resolution of FDG uptake in their tumor following therapy have been shown to have a good prognosis, as compared to those who have residual FDG uptake in their tumors. After treatment it is not necessary to find visible alterations in gross anatomic structure, but some posttreatment effects do occur. Tissue necrosis and concomitant macrophage-mediated inflammation after radiotherapy usually lead to the delay of a follow-up PET scan for 3 to 6 months. Radiographic findings usually peak within 6 to 12 weeks following completion of therapy and resolve by 6 months. The typical appearance on PET is diffuse low-grade or intermediate-grade FDG activity confined to a geographic field corresponding to the radiation port.

Bury et al.,136 in a study of 126 patients with stage I to IHB NSCLC treated with radiation therapy, showed that in detection of residual or recurrent disease FDG-PET had a sensitivity, specificity, accuracy, PPV, and NPV of 100%, 92%, 96%, 92%, and 100%, respectively, and the values for CT were 72%, 95%, 84%, 93%, and 79%. Because of its high sensitivity and negative predictive value, the investigators concluded that FDG-PET was a useful adjunct to CT in monitoring the effects of radiation therapy.

Prognostic Information and Future Trends in PET Imaging

FDG-PET is used in determining planning target volumes (PTV), target coverage, and critical organ dose for radiotherapy. In one study, inclusion of a PET scan resulted in a change in PTV in approximately 30% of the patients137 because of more accurate delineation of metabolically active tumor. In another study, PTV was changed in all patients after inclusion of a PET scan in the preprocedure evaluation.138 It has been shown that FDG uptake in NSCLC correlates with the grade of the primary tumor, but it is an independent risk factor.139 Ahuja et al.140 showed that FDG-PET provides prognostic information that is entirely independent of a tumor's size and clinical stage at the time of diagnosis. When the SUV in the primary tumor was less than 10, the median patient survival was 24.6 months. If it was greater than 10, survivals fell to 11.4 months. If the SUV was greater than 10 and the primary lesion was larger than 3 cm, survival was only 5.7 months. Dhital et al.141 reported that the 1-year survival of patients with tumor SUVmax less than 10 was 75% and with SUVmax greater than 20 it was only 17%.

Radiolabeled thymidine, a marker of DNA synthesis, choline agents (for the evaluation of membrane synthesis and turnover), and radiolabeled amino acids (for the evaluation of protein catabolism), are many of the agents that are under investigation for potential utility in patients with NSCLC.142'143

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