title: Mapping radiation dose distribution on the fractional anisotropy map: applications in the assessment of treatment-induced white matter injury.
abstract: We describe a method to map whole brain radiation dose distribution on to diffusion tensor MR (DT-MR) fractional anisotropy (FA) images and illustrate its applications for studying dose-effect relationships and regional susceptibility in two childhood medulloblastoma survivors. To determine the FA changes voxel-by-voxel in white matter, the post-treatment follow-up FA maps were coregistered to baseline pre-treatment FA maps and automatic segmentation for white matter was carried out. DeltaFA maps representing relative FA change in white matter were hence generated for visual inspection and quantitative analysis. The radiation dose distribution, calculated from radiotherapy plan and exported as images, was coregistered to baseline FA images. DT-MR imaging and processing noise was small with root mean square value of 1.49% for mean DeltaFA. We evaluated the mean DeltaFA changes of regions-of-interest according to radiation dose regions to provide an estimate of the dose-response and found increasing reduction in mean DeltaFA with increasing radiation dose up to 45 Gy after which there was a reversal in the mean FA trend and mean FA approached baseline value. We also found more severe mean FA reduction in the frontal lobes compared to the parietal lobes despite the same radiation dose, suggesting regional susceptibility in the frontal lobe, and mean FA increase in the brainstem after radiation in both patients. We conclude that the method described may be useful in estimating dose-effect relationships and studying regional susceptibility of the brain to radiation in medulloblastoma survivors.
authors.affiliation: Department of Diagnostic Radiology, Blk. K, Rm 406, Queen Mary Hospital, The University of Hong Kong, 102 Pokfulam Road, Hong Kong.
authors.forename: Deqiang
authors.initials: D
authors.lastname: Qiu
authors.forename: Lucullus H T
authors.initials: LH
authors.lastname: Leung
authors.forename: Dora L W
authors.initials: DL
authors.lastname: Kwong
authors.forename: Godfrey C F
authors.initials: GC
authors.lastname: Chan
authors.forename: Pek-Lan
authors.initials: PL
authors.lastname: Khong
mesh_terms: D016880:Anisotropy; D001921:Brain / Q000528:radiation effects*; D001931:Brain Mapping; D001933:Brain Stem / Q000528:radiation effects; D002528:Cerebellar Neoplasms / Q000188:drug therapy / Q000532:radiotherapy* / Q000601:surgery; D002648:Child; D003131:Combined Modality Therapy; D016371:Cranial Irradiation; D038524:Diffusion Magnetic Resonance Imaging; D004307:Dose-Response Relationship, Radiation; D005260:Female; D005625:Frontal Lobe / Q000528:radiation effects; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D008527:Medulloblastoma / Q000188:drug therapy / Q000532:radiotherapy* / Q000601:surgery; D010296:Parietal Lobe / Q000528:radiation effects; D011832:Radiation Injuries / Q000175:diagnosis*; D011879:Radiotherapy Dosage; D018714:Radiotherapy, Adjuvant; D012016:Reference Values; D012680:Sensitivity and Specificity; D017741:Survivors