Author: Yingxuan Chen, Jun Li, Alexis N. Webb 👨🔬
Affiliation: Thomas Jefferson University 🌍
Purpose: Cone-beam computed-tomography (CBCT) is widely used for image-guided therapy. Cumulative dose from repeated CBCT might be a concern. This study aims to measure and compare the CBCT dose for commonly used clinical protocols on a Varian Truebeam and an Elekta VersaHD.
Methods: RaySafe X2 CT Sensor chamber paired with the RaySafe Nested Adult Head and Body CTDI Phantom were used for CTDI measurement. Five commonly used Truebeam CBCT protocols and three VersaHD protocols were included in this study. For each protocol, measurements were taken at the center and at four peripheral positions (top, bottom, left, right) of the phantom. The five measurements were used to calculate the volume CT dose index (CTDIvol) for each protocol, which was then compared with the doses provided by the respective vendor. Additionally, the measured doses from three similar protocols between the two machines were compared.
Results: The measured CTDIvol were 11.7 mGy, 4.2 mGy and 11.09 mGy using the Head and Neck Enhanced, Chest M20 and Pelvis Fast L20 protocol for VersaHD, respectively. Compared with the values provided by the vendor, measurements are higher by 65%, 10%, and 17%. The measured CTDIvol were 3.0mGy, 3.6mGy ,16.2mGy, 34.7mGy, and 12.9 mGy using the Head, Thorax, Pelvis, Pelvis Large, and Spotlight at Truebeam, respectively. Compared with vendor-reported values, the relative differences are -4%, -8%, 2%, -6%, and 5% for each protocol. Comparing the two machines, the largest deviation was observed for the head protocols, with the Head and Neck Enhanced (Elekta) measuring 8.67 mGy greater than the Head (Varian) protocol.
Conclusion: In general, the measured doses showed better agreement with the vendor-reported values for the Truebeam. Comparison of the three most similar protocols between the two machines revealed a minimal dose difference for the chest protocols, but a larger dose difference for the head protocols.