Program Information
Evaluation of the Accuracy of Free-Breathing and Deep Inspiration Breath-Hold Gated Beam Delivery Using An Elekta Linac
M Jermoumi1*, R Xie2 , D Cao1 , D Housley1 , D Shepard1 , (1) Department of Radiation Oncology, Swedish Cancer Institute, Seattle, WA, (2) Ironwood Cancer and Research Centers, Chandler, AZ,
Presentations
SU-F-T-514 (Sunday, July 31, 2016) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose:
In this study, we evaluated the performance of an Elekta linac in the delivery of gated radiotherapy. We examined whether the use of either a short gating window or a long beam hold impacts the accuracy of the delivery
Methods:
The performance of an Elekta linac in the delivery of gated radiotherapy was assessed using a 20cmΧ 20cm open field with the radiation delivered using a range of beam-on and beam-off time periods. Two SBRT plans were used to examine the accuracy of gated beam delivery for clinical treatment plans. For the SBRT cases, tests were performed for both free-breathing based gating and for gated delivery with a simulated breath-hold. A MatriXX 2D ion chamber array was used for data collection, and the gating accuracy was evaluated using gamma score.
Results:
For the 20cmΧ20cm open field, the gated beam delivery agreed closely with the non-gated delivery results. Discrepancies in the agreement, however, began to appear with a 5-to-1 ratio of the beam-off to beam-on. For these tight gating windows, each beam-on segment delivered a small number of monitor units. This finding was confirmed with dose distribution analysis from the delivery of the two VMAT plans where the gamma score(±1%,2%/1mm) showed passing rates in the range of 95% to 100% for gating windows of 25%, 38%, 50%, 63%, 75%, and 83%. Using a simulated sinusoidal breathing signal with a 4 second period, the gamma score of free-breathing gating and breath-hold gating deliveries were measured in the range of 95.7% to 100%.
Conclusion:
The results demonstrate that Elekta linacs can be used to accurately deliver respiratory gated treatments for both free-breathing and breath-hold patients. The accuracy of beams delivered in a gated delivery mode at low small MU proved higher than similar deliveries performed in a non-gated (manually interrupted) fashion.
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