Clinical target volume definition for glioblastoma radiotherapy planning: magnetic resonance imaging and computed tomography.

PURPOSE: To assess the differences between the target delineation using computed tomography (CT) and imaging fusion CT/magnetic resonance imaging (MRI) for the radiotherapy planning of glioblastoma.

METHODS: One hundred-twenty gross tumor volume and clinical target volume on CT and MRI (GTVCT/CTVCT, GTVMRI/CTVMRI, respectively) were contoured and evaluated. The treatments planning (total dose 60 Gy) based on CTVCT were analysed in terms of percentage of CTVCT and CTVMRI receiving 95 % of the prescribed dose (V95-CTVCT, V95-CTVMRI).

RESULTS: GTVs and CTVs contoured on MRI were significantly larger than those delineated on CT (p = 0.0003, p = 0.0006, respectively). Nighty-two percent of CTVCT was coincident with the CTVMRI and 8 % was normal tissue; 20 % of CTVMRI, considered as tumor volume, was not included on CTVCT. The V95-CTVMRI was significantly lower than the V95-CTVCT (p = 0.0005).

CONCLUSIONS: In the delineation of glioblastoma target volume, fusion CT/MRI was preferred. The CT only is insufficient for the CTV dose coverage.