title: Implications of contrast-enhanced CT-based and MRI-based target volume delineations in radiotherapy treatment planning for brain tumors.
abstract: Delineation of various target volumes using contrast-enhanced magnetic resonance imaging (MRI) and/or computed tomography (CT) constitutes the primary step for radiation therapy planning (RTP) in brain tumors. This study presents a quantification and comparative evaluation of the various clinical target volumes (CTV) and gross target volumes (GTV) as outlined by contrast-enhanced CT and MRI, along with its implications for postoperative radiotherapy of brain tumors. Twenty-one patients of gliomas were considered for this prospective study. Peritumoral edema as CTV and residual tumor as GTV were delineated separately in postoperative contrast-enhanced CT and MRI. These volumes were estimated separately and their congruence studied for contrast-enhanced CT and MRI. Compared to MRI, CT underestimated the volumes, with significant differences seen in the mean CTV (mean +/- SD: -62.92 +/- 93.99 cc; P = 0.006) and GTV (mean +/- SD: -21.08 +/- 36.04 cc; P = 0.014). These differences were found to be significant for high-grade gliomas (CTV: P = 0.045; GTV: P = 0.044), while they were statistically insignificant for low-grade gliomas (CTV: P = 0.080; GTV: P = 0.117). The mean differences in the volumes for CTV and GTV were estimated to be -106.7% and -62.6%, respectively, taking the CT volumes as the baseline. Thus, even though, electron density information from CT is essential for RTP, target delineation during postoperative radiotherapy of brain tumors, especially for high-grade tumors, should be based on MRI so as to avoid inadvertent geographical misses, especially in the regions of peritumoral edema.
authors.affiliation: Department of Radiation Oncology, Rajiv Gandhi Cancer Institute and Research Centre, New Delhi, India. nrdatta@yahoo.com
authors.forename: Niloy R
authors.initials: NR
authors.lastname: Datta
authors.forename: Rajasekar
authors.initials: R
authors.lastname: David
authors.forename: Rakesh K
authors.initials: RK
authors.lastname: Gupta
authors.forename: Punita
authors.initials: P
authors.lastname: Lal
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001932:Brain Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D003287:Contrast Media / Q000008:administration & dosage*; D006801:Humans; D008279:Magnetic Resonance Imaging; D008875:Middle Aged; D011446:Prospective Studies; D011880:Radiotherapy Planning, Computer-Assisted; D014057:Tomography, X-Ray Computed
chemical_list: D003287:Contrast Media