In radiotherapy of head and neck cancer (HNC) and non-small cell lung cancer (NSCLC), hypoxia is known to be an important prognostic factor for long-term survival and local tumor control. The PET tracer (18)F-fluoromisonidazole (FMISO) allows noninvasive assessment of tumor hypoxia. This study analyzed whether FMISO PET could predict tumor recurrence after radiotherapy.
Methods: Forty patients with advanced HNC (n = 26) or NSCLC (n = 14) were studied before curative radiotherapy. Dynamic (0-15 min) and static PET scans were acquired up to 4 h after injection of 400 MBq of FMISO. Standardized uptake values (SUVs) and ratios to reference tissues (mediastinum or muscle) were calculated. In addition, time-activity curves up to 14 min after injection were classified visually. PET data were correlated with clinical follow-up data (presence or absence of local recurrence within 1 y), which were available for 21 patients.
Results: For HNC, patients with local recurrence could be separated from disease-free patients by SUV 4 h after injection (all recurrences had an SUV > 2). For NSCLC, no such correlation was observed. The tumor-to-muscle ratios (T/Mu) and tumor-to-mediastinum ratios (T/Me) at 4 h after injection correlated with the risk of relapse in both tumor entities: All patients with a T/Me greater than 2.0 (NSCLC, n = 5) or with a T/Mu greater than 1.6 (HNC, n = 5) presented with tumor recurrence, whereas only 3 of the remaining 11 patients experienced recurrence (27%). Qualitative analysis of time-activity curves for 37 patients revealed 3 curve types (rapid washout, n = 9; intermediate [delayed washout], n = 12; and accumulation, n = 16). Eighteen patients categorized by curve type could be followed up: In 5 of 6 patients with an accumulation curve, disease recurred locally within 1 y, compared with 5 of 8 patients with a delayed-washout curve and 0 of 4 with a rapid-washout curve.
Conclusion: Our results indicate that outcome after radiotherapy can be predicted on the basis of kinetic behavior of FMISO in tumor tissue. An accumulation-type curve, high SUV, and high T/Mu and T/Me at 4 h after injection are highly suggestive of an incomplete response to treatment and might be used to select patients for intensified therapy protocols.