Lack of available funding.

The goal of this protocol is to evaluate the potential of PET imaging of amino acid transport and microglial activation to improve the differentiation of tumor recurrence and radiation necrosis in patients with brain metastases after treatment with stereotactic radiosurgery (SRS) who have re-growing lesions. These state-of-the-art imaging tools will be used in combination with standard magnetic resonance imaging (MRI), MR spectroscopy (MRS) and FDG-PET (fluorodeoxyglucose).

The investigators hypothesize that by using two different PET tracers, one sensitive to tumor metabolic activity, and one sensitive to inflammatory processes, investigators can separately identify metabolically active tumor from radiation necrosis related inflammation. This can be accomplished with quantitative assessments of tracer uptake using kinetic modeling techniques, as well as by high-resolution imaging to assess the distribution of tracer uptake in the tumor region. All participants in the study will have the receive the same diagnostic tests.

Inclusion Criteria:

• Patients over 18 years with brain metastases from melanoma or non-small cell lung cancer
• Patients must have had SRS and regrowth in at least one lesion > 0.5 cm in greatest dimension and fall into one of two categories: a) patient is deemed clinically appropriate for surgical intervention (biopsy or craniotomy) OR b) patient is asymptomatic and has a life expectancy of > 6 months so that serial follow-up imaging is appropriate
• Willingness to participate in imaging studies
• Able to give informed consent

Exclusion Criteria:

• Subjects with history of prior radiation exposure for research purposes within the past year, such that participation in this study would place them over the FDA limits for annual radiation exposure. This guideline is an effective dose of 5 rem received per year.
• Subjects who are pregnant or currently breastfeeding
• Women of child-bearing age who are sexually active, unless they agree to two forms of contraception, and have a negative urine pregnancy test at screening and on the days of the PET imaging
• Patients unable to undergo MRI with gadolinium-based contrast for standard clinical reasons which include:
• Cardiac pacemaker, aneurysm clip, cochlear implants, Intra Uterine Device (IUD), shrapnel, neurostimulators, defibrillator, artificial heart valve, or history of metal fragments in eyes.
• Pregnancy
• Body size too large for closed MRI
• Known hepatic fibrosis.
• Claustrophobia
• Contraindication to MR contrast agents: eGFR (epidermal growth factor receptor) < 30 by the Cockcroft- Gault formula if > 60 years old or with chronic renal disease
• Anaphylactic allergy to gadolinium

Patients who received SRS for melanoma or NSCLC brain metastases with regrowing lesions who are candidates for surgical intervention (biopsy or excision) at the Smilow Cancer Center or are candidates for monitoring by serial imaging will be screened for eligibility and offered enrollment