What are the contouring guidelines for glioma?

Contouring Guidelines for Glioma

The clinical target volume (CTV) for gliomas should include a safety margin of 20 mm outside the gross tumor volume (GTV) in all three dimensions, which can be reduced depending on the grade, histological type, and tumor volume. 1

Imaging for Target Delineation

• MRI should be used in preference to CT scanning as the standard diagnostic tool for glioma contouring, with images taken using the same technique in three dimensions 1
• T1-weighted (with and without contrast medium), T2-weighted MR images and/or fluid-attenuated inversion recovery (FLAIR) imaging should be undertaken as standard 1
• MR images should be converted into a digital format on a numerical support system (e.g., CD) for possible subsequent dosimetric studies 1
• Functional MRI, MR diffusion imaging, MR perfusion studies, and/or proton MR spectroscopy can be combined with standard imaging as options 1
• PET or SPECT scans can be performed in clinical trial settings 1

Gross Tumor Volume (GTV) Definition

• For glioblastoma (WHO grade IV): GTV includes the surgical bed plus residual tumor area identified on T1-weighted MRI with contrast enhancement 1, 2
• For anaplastic gliomas (WHO grade III): GTV includes T2-weighted MRI sequences plus the region of contrast enhancement in T1 3
• For low-grade gliomas (WHO grade II): GTV includes T2/FLAIR abnormalities 2, 3

Clinical Target Volume (CTV) Definition

• For glioblastoma: Based on the EORTC recommendation, CTV should include the resection cavity and residual enhancing regions on T1-sequences with the addition of a 20 mm margin 2
• For anaplastic gliomas: An isotropic expansion of 15 to 20 mm from the GTV is recommended 3
• Currently, a single CTV definition based on postoperative T1/T2 FLAIR abnormalities is recommended, using isotropic margins without the need to cone down 2
• The safety margin can be reduced depending on the grade, histological type, and tumor volume 1
• Anatomical barriers such as ventricles, tentorium, and falx should be respected when defining the CTV 3

Planning Target Volume (PTV)

• A PTV margin based on the individual mask system and image-guided radiation therapy (IGRT) procedures is advised, usually of the order of 3-5 mm 2
• Non-coplanar focalized multiple beam (3-5) should be used to minimize the total fractionated dose delivered to the non-diseased brain 1
• Dose-volume histograms can be useful for defining the best treatment plan 1

Radiation Dose Guidelines

• All fields should be irradiated the same day with a fractionated dose varying from 1.8 to 2 Gy per fraction per day, five times per week 1
• The dose should be adapted according to the histological type and grade of the lesion and should not exceed a total of 60 Gy 1
• For glioblastoma: A total dose of 60 Gy in 30 fractions is usually delivered 3
• For anaplastic gliomas: A dose of 59.4 Gy in 33 fractions is typically given 3

Advanced Techniques and Considerations

• MRI-only workflow shows high level of agreement between GTV and CTV contours with a mean kappa of 0.88 and 0.89, respectively, comparable to CT-MRI workflow 4
• Integration of O-(2-(F-18)fluoroethyl)-l-tyrosine-positron emission tomography/computer tomography (FET-PET/CT) may improve GTV coverage by avoiding larger incongruences between physical and biological imaging techniques, particularly for high-grade gliomas during initial radiotherapy 5
• Intensity-modulated and stereotactic radiotherapy can help deliver a simultaneous integrated boost (SIB) >60 Gy to biologically active tumor regions 3

Special Considerations

• Prophylactic corticosteroid treatment should not be prescribed routinely but can be used to reduce the risk of acute or early-delayed encephalopathy (radiation-induced edema) 1
• Clinical and/or radiological deterioration in the 2 months after the end of radiotherapy should be interpreted with caution and not automatically considered as treatment failure 1
• Patients over 50 years old and/or with previous vascular disease (hypertension, diabetes, hyperlipidemia) have an increased risk for late neurological complications (radionecrosis, radiation-induced leukoencephalopathy) 1

Molecular Considerations for Treatment Planning

• Molecular characterization should complement standard histologic assessment to provide additional diagnostic and prognostic information that may aid in treatment selection 1
• MGMT promoter methylation, IDH mutations, and co-deletions of 1p/19q should be determined depending on the histological and clinical context 1
• Molecular markers can help identify tumor subtypes that may benefit from specific treatment approaches 1