Abstract
PurposeAdvanced radiotherapy delivery systems designed for high‐dose, high‐precision treatments often come equipped with high‐definition multi‐leaf collimators (HD‐MLC) aimed at more finely shaping radiation dose to the target. In this work, we study the effect of a high definition MLC on spine stereotactic body radiation therapy (SBRT) treatment plan quality and plan deliverability.Methods and MaterialsSeventeen spine SBRT cases were planned with VMAT using a standard definition MLC (M120), HD‐MLC, and HD‐MLC with an added objective to reduce monitor units (MU). M120 plans were converted into plans deliverable on an HD‐MLC using in‐house software. Plan quality and plan deliverability as measured by portal dosimetry were compared among the three types of plans.ResultsOnly minor differences were noted in plan quality between the M120 and HD‐MLC plans. Plans generated with the HD‐MLC tended to have better spinal cord sparing (3% reduction in maximum cord dose). HD‐MLC plans on average had 12% more MU and 55% greater modulation complexity as defined by an in‐house metric. HD‐MLC plans also had significantly degraded deliverability. Of the VMAT arcs measured, 94% had lower gamma passing metrics when using the HD‐MLC.ConclusionModest improvements in plan quality were noted when switching from M120 to HD‐MLC at the expense of significantly less accurate deliverability in some cases.
Highlights
The TrueBeam STx and the EDGE linear accelerator from Varian Medical Systems (Palo Alto, CA, USA) are equipped with a number of features designed to facilitate the high-precision, high-accuracy radiation treatment of small targets near critical structures both intra- and extracranially.[1]
The goal of this work was to evaluate the change in plan quality and delivery accuracy when switching from the M120 to high-definition multileaf collimator (HD-MLC), and to test the effect of an added optimization objective aimed at reducing plan modulation on these quality indices
The cases are sorted by the monitor units (MU) of the M120 plan
Summary
The TrueBeam STx and the EDGE linear accelerator from Varian Medical Systems (Palo Alto, CA, USA) are equipped with a number of features designed to facilitate the high-precision, high-accuracy radiation treatment of small targets near critical structures both intra- and extracranially.[1]. The HD-MLC provides essentially twice the resolution along the axis perpendicular to the leaf travel compared to the standard Varian Millennium MLC (M120) which uses 40 central 5 mm-width leaves and 20 outer 10 mm-width leaves in each bank. For inversely optimized treatment plans, the added resolution of the HD-MLC theoretically increases the ability of the optimizer to produce a highly conformal treatment plan, sparing organs at risk (OARs) while providing adequate target coverage This potential increase in plan quality depends on the ability of the optimizer to efficiently and effectively search the allowed solution space and is fundamentally limited by the physical properties of the photon beam and MLC leaves
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