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

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.