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BEST IN PHYSICS (THERAPY): Dosimetric Comparison of 4π and Clinical IMRT for Cortex-Sparing High-Grade Glioma Treatment

K Woods

K Woods1*, R Karunamuni2 , A Tran1 , V Yu1 , D Nguyen1 , J Hattangadi-Gluth2 , K Sheng1 , (1) UCLA School of Medicine, Los Angeles, CA, (2) University of California, San Diego, La Jolla, California


TH-EF-BRB-1 (Thursday, August 4, 2016) 1:00 PM - 2:50 PM Room: Ballroom B

Purpose: Thinning of the cerebral cortex has been observed in patients treated with fractionated partial brain radiation therapy and may contribute to cognitive decline following treatment. The extent of this thinning is dose-dependent, and was shown comparable to that of neurodegenerative diseases such as Alzheimer’s disease at one year post-therapy. This study investigates whether 4π radiotherapy can enable better sparing of the cortex and other critical structures when compared to conventional clinical IMRT plans.

Methods: Clinical cortex-sparing IMRT plans for 15 high-grade glioma patients were included in this study. 4Ï€ radiotherapy plans were created for each patient with 20 intensity-modulated non-coplanar fields selected with a greedy column-generation optimization. All plans were normalized to deliver 100% of the prescribed dose to 95% of the planning target volume (PTV). The mean and maximum dose to the cerebral cortex and other organs at risk (OARs) were compared for the two plan types, as well as the conformity index (CI), homogeneity index (HI), and 50% dose spillage volume (R50).

Results: The 4Ï€ plans significantly reduced the mean cortex dose by an average of 16% (range 6% to 27%) compared to the clinical plans. The mean dose to every other OAR compared was also reduced by 15% to 43%, with statistically significant reductions to the brainstem, chiasm, eyes, optic nerves, subcortical whit, and hippocampus. The average maximum doses were also reduced for 10/12 OARs. The R50 was significantly reduced with the 4Ï€ plans (>14%) and the homogeneity index was significantly improved.

Conclusion: 4Ï€ enables significant sparing of the cerebral cortex when treating high-grade gliomas with fractionated partial brain radiation therapy, potentially reducing the risk of harmful dose-dependent cortical thinning.

Funding Support, Disclosures, and Conflict of Interest: NIH R43CA183390, NIH R01CA188300, Varian Medical Systems

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