Evaluation of PET/MRI for Tumor Volume Delineation for Head and Neck Cancer.
BACKGROUND
Computed tomography (CT), combined positron emitted tomography and CT (PET/CT), and magnetic resonance imaging (MRI) are commonly used in head and neck radiation planning. Hybrid PET/MRI has garnered attention for potential added value in cancer staging and treatment planning. Herein, we compare PET/MRI vs. planning CT for head and neck cancer gross tumor volume (GTV) delineation.


METHODS
We prospectively enrolled patients with head and neck cancer treated with definitive chemoradiation to 60-70 Gy using IMRT. We performed pretreatment contrast-enhanced planning CT and gadolinium-enhanced PET/MRI. Primary and nodal volumes were delineated on planning CT (GTV-CT) prospectively before treatment and PET/MRI (GTV-PET/MRI) retrospectively after treatment. GTV-PET/MRI was compared to GTV-CT using separate rigid registrations for each tumor volume. The Dice similarity coefficient (DSC) metric evaluating spatial overlap and modified Hausdorff distance (mHD) evaluating mean orthogonal distance difference were calculated. Minimum dose to 95% of GTVs (D95) was compared.


RESULTS
Eleven patients were evaluable (10 oropharynx, 1 larynx). Nine patients had evaluable primary tumor GTVs and seven patients had evaluable nodal GTVs. Mean primary GTV-CT and GTV-PET/MRI size were 13.2 and 14.3 cc, with mean intersection 8.7 cc, DSC 0.63, and mHD 1.6 mm. D95 was 65.3 Gy for primary GTV-CT vs. 65.2 Gy for primary GTV-PET/MRI. Mean nodal GTV-CT and GTV-PET/MRI size were 19.0 and 23.0 cc, with mean intersection 14.4 cc, DSC 0.69, and mHD 2.3 mm. D95 was 62.3 Gy for both nodal GTV-CT and GTV-PET/MRI.


CONCLUSIONS
In this series of patients with head and neck (primarily oropharynx) cancer, PET/MRI and CT-GTVs had similar volumes (though there were individual cases with larger differences) with overall small discrepancies in spatial overlap, small mean orthogonal distance differences, and similar radiation doses.
Department of Radiation Oncology, University of North Carolina Hospitals , Chapel Hill, NC , USA.
Kyle
K
Wang
Department of Radiation Oncology, University of North Carolina Hospitals , Chapel Hill, NC , USA.
Brandon T
BT
Mullins
Department of Radiation Oncology, University of North Carolina Hospitals , Chapel Hill, NC , USA.
Aaron D
AD
Falchook
Department of Radiation Oncology, University of North Carolina Hospitals , Chapel Hill, NC , USA.
Jun
J
Lian
State Key Laboratory for Novel Software Technology, Nanjing University , Nanjing , China.
Kelei
K
He
Department of Radiology, University of North Carolina Hospitals , Chapel Hill, NC , USA.
Dinggang
D
Shen
Department of Radiation Oncology, University of North Carolina Hospitals , Chapel Hill, NC , USA.
Michael
M
Dance
Department of Radiology, University of North Carolina Hospitals , Chapel Hill, NC , USA.
Weili
W
Lin
Department of Radiology, University of North Carolina Hospitals , Chapel Hill, NC , USA.
Tiffany M
TM
Sills
Department of Radiation Oncology, University of North Carolina Hospitals , Chapel Hill, NC , USA.
Shiva K
SK
Das
Department of Radiology, University of North Carolina Hospitals , Chapel Hill, NC , USA.
Benjamin Y
BY
Huang
Department of Radiation Oncology, University of North Carolina Hospitals , Chapel Hill, NC , USA.
Bhishamjit S
BS
Chera
CT; GTV; PET/MRI; head and neck cancer; radiation treatment planning