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Evaluation of Volumetric Modulated Arc Therapy (VMAT) Efficiency Using the Elekta Agility

J Moore

J Moore*, K Smith, M Duhon, J Qian, R Gonzales, T McNutt, J Wong, Johns Hopkins University, Baltimore, MD

SU-E-T-394 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To evaluate the efficiency of VMAT delivery using the Elekta Agility head with 160 5mm leaves. The Agility head is promoted as having significantly faster leaf motion and therefore delivery time. Improvement of efficiency allows for more patients to be treated in a day and reduces the time that each patient must be on the treatment table.
Methods: Six plans initially treated on an 80-leaf Elekta Infinity were selected. The sites represented were Pancreas, two Head and Neck plans, Pelvis, Retroperitoneal Mass, and Rectal. For each plan, a film measurement in a 30x30x30 cm phantom is conducted. The beam-on time of each plan delivery is recorded. To compare plans with the 160-leaf Agility, the plans optimized for the 80-leaf Infinity are converted to 160-leaf plans by pairing adjacent MLC leaves. This produces a plan in which the aperture shapes on both machines are matched. Additionally, another plan is optimized using the 160-leaf Agility to show the improved capabilities of the higher resolution device.
Results: The plans delivered on the 80-leaf Infinity took on average 273 seconds to deliver. On the 160-leaf Agility, paired plans took on average 112 seconds to deliver. The re-optimized Agility plans took on average 204 seconds to deliver. All of the paired plans took significantly less time (less than half) to deliver (p<0.01). Plans re-optimized for the Agility took significantly less time on average (p=0.02), however one plan did result in an increase in delivery time from 267 seconds to 298 seconds.
Conclusion: The Agility head is shown to greatly improve the efficiency of VMAT delivery when compared to the Infinity. Additional research is needed to refine the planning objectives to reduce treatment time when optimized using the Agility MLC.

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