Room: Exhibit Hall | Forum 9
Purpose: Cherenkov imaging has been used to analyze dose distribution in radiation therapies, including TSET. However, disagreement has been detected between dose measurement from diodes and Cherenkov measurement from different angle perspective. This study focuses on the angular dependence of Cherenkov signals to dose deposition. The angular correction factors are calculated in this study to compensate for the dose distribution derived from the Cherenkov analysis.
Methods: Tissue simulating phantoms are placed vertically at the location of the TSET patient. Arrays of diodes are taped vertically on the side of the phantoms facing the LINAC head to measure the dose on the corresponding locations. The time-gated intensified Cherenkov camera acquires the video frames with distributions of the Cherenkov signal generated from the phantom. The Linac delivers the electron beam towards the phantoms with different angles to the horizontal. The correction factors for different location in the camera image are derived from the angles to the horizontal that are used in the TSET treatment. These correction factors are applied to the Cherenkov images taken for the patient in TSET treatment to analysis the distribution deposited on the patient body. Monte-Carlo simulation will be performed to understand the cause of the perspective correction factor.
Results: The measurements of dose and Cherenkov intensity are normalized and compared in both horizontal and vertical directions. In the vertical direction, the correction factors, defined as ratios between the dose and Cherenkov intensity, change from 1.0 to a function of off-axis distances CF(y) (varies from 0.5 to 2.0) when the incident angle of electrons change from 0 to 16 degrees.
Conclusion: The study shows an angular dependence in vertical direction of Cherenkov signal to dose, which needs to be corrected by a perspective correction factor in order to convert Cherenkov imaging to dose map.