Multi-Tracer PET Assessment of Primary Brain Tumors

The standard treatment approach for patients with high-grade primary brain tumors includes maximum feasible surgical resection, followed by 6 weeks of concurrent cranial irradiation and daily low-dose temozolomide chemotherapy, followed by 12 cycles of high-dose temozolomide administered for 5 consecutive days every 4 weeks \[Stupp 2005\]. Contrast-enhanced MRI is the current standard for evaluating the success of therapy and monitoring for tumor recurrence. MRI is typically obtained prior to initial surgery, within 24 hours after surgery, at the conclusions of cranial irradiation, and then every 8 weeks during temozolomide chemotherapy until evidence of recurrence. Despite this careful clinical and radiographic surveillance, and despite decades of research into the histologic and molecular classification of primary brain tumors, our ability to predict tumor behavior remains very limited. Some gliomas will result in overall survival times of only months, whereas other histologically-identical gliomas may yield survivals of years to decades \[Carson 2007, Curran 1993, Lamborn 2004\]. Current assessment of tumor response to therapy is also poor. Patients with complete radiographic response after cranial irradiation often progress rapidly post-irradiation. In contrast, some patients with enhancing masses at the end of chemoradiotherapy may respond dramatically to further chemotherapy alone, or the masses may even disappear in the absence of further therapy (so called "tumor pseudoprogression") \[Chamberlain 2007\]. This confounding situation demonstrates a need for better assessment of tumor response.