The purpose of this study is to see if 18F-fluciclovine (Axumin®) PET imaging is useful and safe in the management of children with High Grade Gliomas. Investigators seek to determine if this imaging will help doctors tell the difference between tumor growth (progression) and other tumor changes that can occur after treatment.

Following radiation and immunotherapy, many pediatric participants with high-grade gliomas (HGG), including diffuse midline glioma (DMG), demonstrate radiographic findings suspicious of disease progression. Differentiating post-treatment changes from true tumor progression is paramount to clinical decision-making, as true tumor progression may warrant a change in treatment, while post-treatment changes are typically not an indication to change treatment. Unfortunately, conventional MRI cannot reliably distinguish between true progression and post-treatment changes. Therefore, finding a physiological correlate to delineate true progression from pseudo-progression is critical.

The overall objective of this current application is to evaluate 18F-fluciclovine PET imaging as a diagnostic biomarker for tumor progression compared to post-treatment changes in pediatric HGG. The long-term goal of this research is to accurately differentiate tumor progression from post-treatment changes in pediatric HGG using 18F-fluciclovine PET imaging.

Inclusion Criteria

• 1. Histopathology-proven HGG (WHO grade III-IV) or DMG (WHO grade IV) or, in the case of DMG of the pons, imaging that is characteristic of Diffuse intrinsic pontine gliomas (DIPG) (diffusely infiltrating >=2/3 of the pons).
• 2. Measurable disease, measuring at least 1x1 cm.
• 3. Life expectancy of greater than 8 weeks.
• 4. Age > 1 years but < 21 years of age at enrollment.

For those without planned surgery:

• 1. Participants with clinical and/or radiographic suspicion of True progression (TP) or Pseudoprogression (PsP) during radiation but yet to have the initial post-radiation MRI scan.

or

• 2. Participants with suspicion for TP or PsP on first post-radiation MRI

For those with planned surgery:

• 1. Clinical or radiographic suspicion of tumor progression with plan to undergo surgery or biopsy.

Exclusion Criteria:

• 1. Inability to tolerate imaging procedures in the opinion of an investigator or treating physician.

• 2. Pregnant or breastfeeding participants.

• 3. Participant who would require sedation or anesthesia for imaging beyond standard of care (SOC).

• 4. Participants who weigh less than 8 kg.

• 5. Participants who cannot avoid contact with a pregnant woman or infant for at least 12 hours following injection.

• 6. Participants with a history of abnormal kidney function or creatinine >= CTCAE v5.0 grade 2 at time of study registration.

  7. Participants with primary tumors of the spinal cord.