Methionine and PBR28-PET (Peripheral Benzodiazepine Receptors) in Brain Metastases Following Radiosurgery

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