Development of the next generation radiation therapy based on molecular imaging

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To visualize intratumoral hypoxic areas and their reoxygenation before and during fractionated radiation therapy (RT), 18F-fluoromisonidazole positron emission tomography and computed tomography (F-MISO PET/CT) were performed. Ten patients, consisting of four head and neck cancers, four gastrointestinal cancers, one lung cancer, and one uterine cancer, were included. F-MISO PET/CT was performed twice before RT and during fractionated RT of approximately 20 Gy/10 fractions for eight of the 10 patients. F-MISO maximum standardized uptake values (SUVmax) of normal muscles and tumors were measured. The tumor-to-muscle (T/M) ratios of F-MISO SUVmax were also calculated. Mean SUVmax ± standard deviation (SD) of normal muscles was 1.25 ± 0.17, and SUVmax above the mean + 2 SD (≧1.60 SUV) was regarded as a hypoxic area. Nine of the 10 tumors had an F-MISO SUVmax of equal to or more than 1.60. All eight tumors examined twice showed a decrease in SUVmax, T/M ratio, or percentage of hypoxic volume (F-MISO ≧1.60) at approximately 20 Gy, indicating reoxygenation. In conclusion, accumulation of F-MISO of ≧1.60 SUV was regarded as an intratumoral hypoxic area in our F-MISO PET/CT system. Most human tumors (90%) in this small series had hypoxic areas before RT, although hypoxic volume was minimal (0.0-0.3%) for four of the 10 tumors. In addition, reoxygenation was observed in most tumors at two weeks of the fractionated RT.