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Sectional Optimization of Collimator Angles in VMAT for Multiple Brain Metastases

R Nanatsue*, F Araki , T Ohno , Kumamoto University, Kumamoto, 43


(Sunday, 7/14/2019)  

Room: ePoster Forums

Purpose: To reduce the dose to normal brain by optimizing sectionally collimator angles in volumetric modulated arc therapy (VMAT) for multiple brain metastases.

Methods: VMAT plans with a collimator angle of 45 degrees (standard plan) were created for 7 patients with three or four multiple brain metastases using an analytic anisotropic algorithm (AAA) in an Eclipse (ver. 10.1). To find optimal collimator angles, the RT-structure files were converted from TPS to the MATLAB files. The projected images of targets from beams eye’s views were created in a gantry angle range of 0 to 360 degrees. The optimal collimator angles were decided to minimize the island block problem area (IBPA) which was calculated using projected images. The optimal collimator angles at each sectional arc was calculated for VMAT plans with 9-arcs (every 40°), 6-arcs (60 °) and 4-arcs (90 °). Finally, the VMAT dose distributions were compared between a 1-arc VMAT plan with an optimal collimator angle (1-arc optimal plan), sectional VMAT plans with each optimal collimator angle (sectional arc optimal plan), and a standard plan.

Results: The Vâ‚?12Gyâ‚Ž and mean dose of normal brain for the 1-arc optimal plan decreased by 13.6% and 11.6% compared to those of the standard plan, respectively. The maximum doses in brain stem and optic nerves reduced by 58.7% and 49.6% compared to those of the standard plan, respectively. Similarly, Vâ‚?12Gyâ‚Ž and mean dose of normal brain for the sectional arc optimal plan further decreased compared to that of the 1-arc optimal plan in 7 patients. The optimal number of sectional arcs for the dose reduction of normal brain depends on the number of tumors and its location.

Conclusion: The sectional VMAT plan with each optimal collimator angle for multiple brain metastases was useful to reduce the dose of normal brain and OARs.


Optimization, MLC, Brain


TH- External beam- photons: VMAT dose optimization algorithms

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