Program Information
Dosimetric Impact of Multileaf Collimator Leaf Width On Stereotactic Radiosurgery (SRS) RapidArc Treatment Plans for Single and Multiple Brain Metastases
S Hossain*, V Keeling , S Ahmad , O Algan , University of Oklahoma Health Sciences Center, Oklahoma City, OK
Presentations
SU-E-T-331 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose:To determine the effects of multileaf collimator (MLC) leaf width on normal-brain-tissue doses and dose conformity of SRS RapidArc treatment plans for brain tumors.
Methods:Ten patients with 24 intracranial tumors (seven with 1-2 and three with 4-6 lesions) were planned using RapidArc for both Varian Millennium 120 MLC (5 mm leaf width) and high definition (HD) MLC (2.5 mm leaf width). Between 2 and 8 arcs were used with two full coplanar arcs and the rest non-coplanar half arcs. 6 MV beams were used and plans were optimized with a high priority to the Normal Tissue Objective (to achieve dose conformity and sharp dose fall-off) and normal brain tissue. Calculation was done using AAA on a 1 mm grid size. The prescription dose ranged from 14-22 Gy. Plans were normalized such that 99% of the target received the prescription dose. Identical beam geometries, optimizations, calculations, and normalizations were used for both plans. Paddick Conformity Index (PCI), V4, V8 and V12 Gy for normal brain tissue and Integral Dose were used for analysis.
Results:In all cases, HD MLC plans performed better in sparing normal brain tissue, achieving a higher PCI with a lower Integral Dose. The average PCI for all 24 targets was 0.75±0.23 and 0.70±0.23 (p ≤0.0015) for HD MLC and Millennium MLC plans, respectively. The average ratio of normal brain doses for Millennium MLC to HD MLC plans was 1.30±0.16, 1.27±0.15, and 1.31±0.18 for the V4, V8, and V12, respectively. The differences in normal brain dose for all criteria were statistically significant with p-value < 0.02. On average Millennium MLC plans had a 16% higher integral dose than HD MLC plans.
Conclusion:Significantly better dose conformity with reduced volume of normal brain tissue and integral dose was achieved with HD MLC plans compared to Millennium MLC plans.
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