Program Information
Patient-Specific QA for MLC-Equipped Robotic Radiosurgery Using a High-Resolution EPID
B Han*, L Xing , L Wang , Stanford Univ School of Medicine, Stanford, CA
Presentations
TH-AB-FS1-11 (Thursday, August 3, 2017) 7:30 AM - 9:30 AM Room: Four Seasons 1
Purpose: To systematically investigate a high spatial-resolution (0.2mm) electronic portal imaging device (EPID) for patient-specific quality assurance (QA) of MLC-equipped CyberKnife (CK).
Methods: An EPID-based dosimetric measurement technique is applied to CK radiosurgery plan dose distribution measurement. A Monte Carlo (MC) simulated pixel-to-pixel EPID response specific to CK is used to convert a raw EPID-measured image of a radiosurgery treatment field into water-based dose distribution. Physics verification plans were generated from original brain and prostate patient plans and set to deliver all treatment segments at the same beam direction perpendicular to a plastic water phantom with the size of 20cmx20cmx10cm. The dose distributions were measured using the EPID with a 2cm thick plastic water build-up slab. The raw EPID measurements were converted into planar doses in a water phantom at 1.5cm depth and compared with EBT2 film measurement. Gamma-index and MLC leaf positional accuracy were analyzed to estimate the treatment delivery accuracy.
Results: For both brain and prostate plans, the EPID measured dose distributions are in good agreement with the film measurements. The brain plan contained 92 segments with a total MU of 31573. The prostate plan contained 100 segments with a total MU of 28054. Comparing EPID and film measurements, the (3%,2mm) gamma-index pass rates are 92.6% and 95.1% for the brain and prostate plans, respectively. The mean EPID detected leaf position deviation from treatment plan is 0.5mm. The high detector density EPID is able to record and measure the whole radiosurgery plan delivery and identify the field edge segment by segment. The dose result can be analyzed in real time. Therefore, the QA setup and data processing time is greatly reduced comparing to film dosimetry.
Conclusion: The high spatial-resolution EPID is proved to be an accurate and efficient patient-specific QA tool for MLC-based radiosurgery treatment.
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