Utilizing 18F-fluoroethyl-l-tyrosine positron emission tomography in high grade glioma for radiation treatment planning in patients with contraindications to MRI.

INTRODUCTION: Patients with high grade glioma (HGG) and contraindications to magnetic resonance imaging (MRI) are dependent on contrast-enhanced computerized tomography (CT) scan imaging for radiation therapy (RT) target volume delineation. This study reviews the experience with the utilization of 18F-fluoroethyl-l-tyrosine positron emission tomography (FET-PET) to define residual disease post craniotomy and optimize RT planning.

METHODS: Patients with HGG and a contraindication to MRI managed with radiation therapy between 2007 and 2015 were identified. RT target volumes including gross tumour volume (GTV) defined by CT-alone and the biological target volume (BTV) defined by PET-CT were recorded. Clinical target volumes (CTV) were created from the GTV and BTV respectively using standard protocol volume expansion. The expanded BTV was termed clinical target volume biological (CTV-B). Union and intersection between CTV and CTV-B, conformity index, volumetric parameters and individual patient outcomes were analysed.

RESULTS: Six patients fit study criteria. There was a mean increase in CTV-B from CTV by 31.6% with a conformity index of 0.78. Two out of six patients had FET-PET avid disease outside the constructed PTV when delineated by CT-alone. One patient with CT-only planning had a new contrast-enhancing mass within 1 month of completing RT, suggesting potential geographical miss.

CONCLUSION: Patients with contraindication to MRI the addition of FET-PET can improve target volume delineation for RT Planning.