PET is clearly accepted for lung cancer staging while deciding on potentially operative therapy. For restaging, Medicare accepts it as follows: PET is covered for restaging: (1) after completion of treatment for the purpose of detecting residual disease, (2) for detecting suspected recurrence or metastasis, (3) to determine the extent of a known recurrence, or (4) if it could potentially replace one or more conventional imaging studies when it is expected that conventional study information is insufficient for the clinical management of the patient. Restaging applies to testing after a course of treatment is completed, and is covered subject to the conditions above.
The literature supports PET for restaging. PET has been investigated in 3 different scenarios: restaging after neoadjuvant therapy, early assessment of response to therapy, and restaging after completion of therapy. In the first scenario, PET could be used after induction chemotherapy or chemoradiation to evaluate for tumor resectability. Few studies have been performed to investigate the reliability of PET in assessing mediastinal “downstaging.” From the studies that are available, it appears that there is much variability in the results. Studies evaluating for a complete pathologic response appear to have high false-positive and false-negative rates. The second scenario was investigated in a study of 57 patients who were evaluated by PET 1 wk before and 3 wk after the first cycle of chemotherapy. It was found that a reduction in metabolic activity correlated closely with the final outcome of the therapy. An early metabolic response predicted better survival, and a poor response predicted disease progression within the first 3 cycles of chemotherapy. The impact of this evaluation on the morbidity and cost of nonresponding tumors suggests much merit in this strategy. The third scenario is the most commonly performed scenario for restaging. Multiple studies have demonstrated a high specificity for the characterization of viable tumor and scar tissue after therapy. Furthermore, Patz et al. have shown that 18F-FDG PET has prognostic value and correlates strongly with rates of survival of patients with treated lung cancer; patients with positive 18F-FDG PET results have a significantly worse prognosis than patients with negative results. Hicks et al. demonstrated a significant impact of PET on further management, with major changes being made in 63% of studied cases.
However, NCCN does not clearly recommend PET on p. MS-23-25 for restaging on therapy. SNM(Revised February 2011) does not recommend it for restaging either.
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