Program Information
Commissioning of Breath-Hold for Motion Management of Stereotactic Body Radiation Therapy Using a Six Degrees-Of-Freedom Motion Platform and Three-Dimensional Diode Array
J James*, A Cetnar , B Wang , University of Louisville, Louisville, KY
Presentations
PO-BPC-Exhibit Hall-4 (Saturday, March 7, 2015) Room: Exhibit Hall
Purpose: The motivation for using breath-hold as a motion management technique for SBRT instead of respiratory gating is that it allows you to acquire a pre-treatment cone beam CT for direct setup verification. In order to commission breath-hold for motion management of SBRT, a six degrees-of-freedom motion platform and three-dimensional diode array was used.
Methods: Respiratory waveforms that include a breath-hold period were created for varying levels of deep inspiration breath hold (DIBH) and breath-hold at end of expiration. These waveforms were then used in conjunction with the Scandidos Hexamotion motion platform to create planning CTs of the Scandidos Delta4 three-dimensional diode array in the breath-hold position. VMAT plans were optimized for each breath-hold CT and delivered to the Delta4 phantom using the Varian TrueBeam gating system in breath-hold mode. The expected dose was compared to the delivered dose using a gamma analysis. In addition, the breath-hold gating limits were investigated to determine how wide the gating range can be with acceptable dosimetric accuracy.
Results: Each breath-hold treatment delivery had a gamma passing rate within our clinical criteria, ranging from 99.7% to 100.0% for 3%/3mm and 96.3% to 99.0% for 2%/2mm. When allowing the breath-hold waveform to drift between gating limits or to hold steady at one extreme of the gating range, the gamma passing rates decreased as expected. The most significant decrease occurred when increasing the gating range from 4mm to 5mm. The 3%/3mm and 2%/2mm gamma pass rates decreased from 99.7% to 95.7% and from 95.1% to 72.9%, respectively.
Conclusion: Breath-hold was shown to be an effective and dosimetrically accurate way to provide motion management for SBRT using the TrueBeam gating system. We recommend the use of a 4mm gating window when implementing breath-hold in the clinic to provide the proper balance between treatment efficiency and dosimetric accuracy.
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