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 (GTV_CT/ CTV_CT, GTV_MRI/CTV_MRI, respectively) were contoured and evaluated. The treatments planning (total dose 60 Gy) based on CTV_CT were analysed in terms of percentage of CTV_CT and CTV_MRI receiving 95 % of the prescribed dose (V₉₅-CTV _CT, V₉₅-CTV_MRI). 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 CTV_CT was coincident with the CTV_MRI and 8 % was normal tissue; 20 % of CTV_MRI, considered as tumor volume, was not included on CTV _CT. The V₉₅-CTV_MRI was significantly lower than the V₉₅-CTV_CT (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.