Radiotherapy (RT) is one of the most important local treatments besides surgery, but currently, no consensus has been made regarding the optimal radiation volume for high grade gliomas. The most main growth characteristics of glioblastoma is infiltrative growth through the white matter tracts, regions along the white matter tracts especially at the direction of the main fiber bundles would have a higher risk of microscopic tumor cell dissemination. However, in current practice, recommends for the CTV definition is adding a 2 cm symmetrical margin to GTV or peritumoral edema in all directions, which hardly account for the growth characteristics of gliomas that are known from histopathological findings.

Patients with glioblastoma were recruited for this study based on the following eligibility criteria: Age between 18 and 70, performance status of 0-1 (Eastern Cooperative Oncology Group performance status), histologically confirmed glioblastoma, no cerebrospinal fluid and distant metastatic disease. All patients had adequate hematologic, hepatic, and renal function. Patients younger than 18 years; patients with a prior (i.e. within 5 years) or synchronous malignancy, other than non-melanoma skin cancer; and those with significant comorbidities were excluded.

Eligible patients received chemoradiotherapy (CRT) ( PTV-GTV: 60Gy at 2.0Gy per fraction, 5 fractions per week for 6 weeks; PTV-CTV: 54Gy at 1.8Gy per fraction, 5 fractions per week for 6 weeks) with a Temozolomide (TMZ) regimen（75mg/m2 per day during RT）, followed by 6 additional cycles of TMZ. (150 mg/m2 for the first cycle and 200 mg/m2 for the 2-6th cycles, on days 1-5, every 4 weeks) .

The investigators established a detailed protocol for target delineation of the CTV based on brain anatomy, white mater fiber tracts distribution and the growth patterns of tumor. Briefly, along the directions of the main nerve fiber bundles ，the CTV is defined as peritumoral edema plus 1cm. while in other directions, the CTV is defined as GTV plus 2cm and should be adjusted to anatomical borders such as the skull (0 mm, using bone window), ventricles (5 mm), falx (0 mm), tentorium cerebelli (0 mm), visual pathway/optic chiasm and brainstem (each 0 mm) and modified to include all regions of abnormal T2/FLAIR MRI signal. Deep brain white matter is the focus for RT target contour, regions of normal uninvolved gray matter should be modified to be protected.

Inclusion Criteria:

• Age between 18-70 years
• performance status of 0-1 (Eastern Cooperative Oncology Group performance status)
• histologically confirmed glioblastoma
• no cerebrospinal fluid and distant metastatic disease
• All patients had adequate hematologic, hepatic, and renal function.

Exclusion Criteria:

• younger than 18 years;
• patients with a prior (i.e. within 5 years) or synchronous malignancy, other than non-melanoma skin cancer; and those with significant comorbidities