(Saturday, 4/4/2020) [Mountain Time (GMT-6)]
Purpose: To quantify beam-off latency time of RPM gating as a part of the development of a comprehensive quality assurance program for RPM commissioning suggested in TG-142.
Methods: A treatment plan was generated to deliver 400 MU of a static slit pattern created by a single 3mm leaf opening (Varian Edge linac). A respiratory motion phantom containing Gafchromic film was irradiated at a fixed 8 breath-per-minute sinusoidal pattern. Gated irradiation was repeated with six different gating window widths, as well as static non-gated irradiation with no phantom motion. Dose profiles of the irradiated slit patterns were analyzed using DoseLab to measure FWHM for each gating width.
Results: A linear relationship was observed between the irradiated FWHM and gating window. Extrapolation to a “zero” width gating window reveals a delta between gated and true static irradiation FWHM, which allows for quantification of beam gating cutoff time.
Conclusion: Measurement of dose slit pattern width of a series of gating windows during fixed-speed motion may enable quantification of beam gating cutoff time per TG-142 recommendation. Measurement at different motion speeds may be necessary to enhance temporal resolution of cutoff time measurement.
Contact Email
