Changes of gray matter volume during radiotherapy of nasopharyngeal carcinoma

There were 21 cases of nasopharyngeal carcinoma, including 17 male cases and 4 female cases, with an age range of 27~68 years old and an average age of 50 years. Patients underwent three MRI cranial imaging scans during radiation therapy, before radiation therapy (1-2 days before radiation start), during radiation therapy (19-20 days after radiation start), and after radiation therapy (1 to 2 days after radiation therapy ended). All MRI images used the same full-body Philips Achieva 3.0T imaging system and an eight-channel head coil (Philips Healthcare, Netherlands).3D-T1 weighted imaging parameters: repeat time = 30 ms, echo time = 2000 ms, flip angle = 8., field of view = 240×240 mm, layer thickness = 2 mm, voxel template size = 1 mm×1 mm×1 mm, matrix = 256×256, scan time = 4 min 59 s.The SPM 8 and VBM 8 software were run on the MATLAB (R2018a) platform to perform data preprocessing of the T1 structured image. Firstly, the DICOM format image is converted to NIFTI format, and VBM 8 software is used to segment the image to obtain gray matter, white matter and cerebrospinal fluid images. Normalize the segmented image to the MNI standard template with voxel sizes of 1.5mm×1.5mm×1.5mm; Smooth nuclei with a half-height full width (FWHM) of 8mm×8mm×8mm were used for spatial smoothing to obtain a brain gray matter map.