Program Information
Reduction of Normal Brain Dose by Optimizing Irradiation Angles for VMAT in Multiple Brain Metastases
N Yamaura*, F Araki , T Ohno , Kumamoto University, Kumamoto, Kumamoto
Presentations
SU-I-GPD-T-339 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: To reduce dose to normal brain by optimizing irradiation angles for VMAT in multiple brain metastases.
Methods: The VMAT plan with single arc and at single isocenter in four brain metastases was created by the Acuros XB algorithm (Eclipse ver.10). The calculation voxel size was 1 × 1 × 1.25 mm³. The prescription dose was 24Gy/3 fractions. The projection images from a beams eye’s view at each control point (CP) were calculated from a DICOM-RT file. An island blocking problem area (IBPA) is unblocked irradiation area in normal brain generated by sharing the same MLC-leaf pairs between multiple targets. The IBPA was calculated to optimize optimal irradiated directions (table angles of 350-10 degrees and collimator angles of 1-165 degrees) at each CP. The IBPAs at all CPs were integrated. A combination of optimized table and collimator angles was derived from minimum integrated IBPA. The usefulness of the optimized table and collimator angles to reduce the normal brain dose was confirmed by a comparison of dose volume histograms (DVHs) between minimum and maximum integrated IBPAs.
Results: The minimum integrated IBPA was 432 mm² at the combination of table and collimator angles of 350 and 21 degrees, respectively. Similarly, the maximum integrated IBPA was 3399 mm² at the combination of 5 and 90 degrees. DVHs for four PTVs were equivalent between minimum and maximum integrated IBPA. The mean dose in normal brain in the VMAT plan with the minimum integrated IBPA reduced by 11.8% compared to that with the maximum integrated IBPA. Similarly, MU reduced by 24% in VMAT plan with the minimum integrated IBPA.
Conclusion: It makes it possible to reduce the normal brain dose and MU for VMAT in multiple brain metastases, by use of the minimum integrated IBPA derived by optimizing table and collimator angles.
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