Radionecrosis of the frontal lobe as a consequence of malignant ethmoid tumor management: incidence, diagnosis, risk factors, prevention and management.

Malignant ethmoid tumors are treated by surgery followed by radiotherapy. This study aimed to evaluate the incidence, risk factors and outcome of radionecrosis of frontal lobe and determine preventive measures. Retrospective study of ethmoid malignancies treated from 2000 to 2011. All patients underwent surgery with/without anterior skull base resection using endoscopic or external approaches followed by irradiation (mean dose 64 Gy). Median follow-up was 50 months. Eight of 50 patients (16 %) presented with fronto-basal radionecrosis, connected to duraplasty, with a latent interval of 18.5 months. Although asymptomatic in six, radionecrosis triggered seizures and required surgery in two cases. Survival was not impacted. Risk factors included dyslipidemia, occurrence of epilepsy and dural resection. Radionecrosis may result from the combination of anterior skull base resection and radiotherapy for the treatment of ethmoid malignancies. Preventive measures rely on improving the duraplasty and optimization of the Gy-dose delivery.

Mapping radiation dose distribution on the fractional anisotropy map: applications in the assessment of treatment-induced white matter injury.

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.