Serial PET studies of human cerebral malignancy with [1-¹¹C]putrescine and [1-¹¹C]2-deoxy-D-glucose

Serial PET measurements of [1-¹¹C]putrescine ([¹¹C]PUT) uptake and glucose metabolic rate (GMR) using [1-¹¹C]2-deoxy-D-glucose ([¹¹C]2DG) were made on eight human subjects with a radiological and, in most cases, pathological diagnosis of primary or metastatic brain tumor. Blood-to-brain influx constants (K(i)) were calculated for [¹¹C]PUT. Tumor uptake of ¹¹C after [¹¹C]PUT injection was unidirectional peaking at 15 min. The mean ± s.d. K(i)s for [¹¹C]PUT for tumor and normal brain tissue were 0.078 ± 0.045 and 0.024 ± 0.007 ml cc^-1 min^-1, respectively (average of ratio, 3.11) whereas the ratio of GMR for tumor and normal brain tissue was 1.2 ± 0.5. The mean K(i) for four active, high grade astrocytomas was 0.098 ± 0.030 in contrast to 0.027 ± 0.008 ml cc^-1 min^-1 for two patients with low grade astrocytoma. Active high grade astrocytomas also showed marked CT contrast enhancement and regional glucose hypermetabolism. In one subject with brain metatases, both [¹¹C]PUT and GMR correlated with a declining clinical picture in repeated studies over a 4-mo period. PET studies with [¹¹C]PUT provide a better signal:noise ratio than GMR measurements, are useful for locating small glycolytically hypometabolic tumors and, when used in longitudinal studies in a single subject, appear to provide an index of degree of malignancy.