Evaluation of radiotherapy setup accuracy for head and neck cancer using a 3-D surface imaging system

The purpose of this study was to measure the accuracy of a three-dimensional surface imaging system (3-D SIS) in comparison to a 3-laser system by analyzing the setup errors obtained from a RANDO Phantom and head and neck cancer patients. The 3-D SIS used for the evaluation of the setup errors was a C-RAD Sentinel. In the phantom study, the OBI setup errors without the thermoplastic mask of the 3-laser system vs. the 3-D SIS were measured. Furthermore, the setup errors with the thermoplastic mask of the 3-laser system vs. the 3-D SIS were measured. After comparison of the CBCT, setup correction about 1 mm was performed in a few cases. The probability of the error without the thermoplastic mask exceeding 1 mm in the 3-laser system vs. the 3-D SIS was 75.00% vs. 35.00% on the X-axis, 80.00% vs. 40.00% on the Y-axis, and 80.00% vs. 65.00% on the Z-axis. Moreover, the probability of the error with the thermoplastic mask exceeding 1 mm in the 3-laser system vs. the 3-D SIS was 70.00% vs. 15.00% on the X-axis, 75.00% vs. 25.00% on the Y-axis, and 70.00% vs. 35.00% on the Z-axis. These results showed that the 3-D SIS has a lower probability of setup error than the 3-laser system for the phantom. For the patients, the setup errors of the 3-laser system vs. the 3-D SIS were measured. The probability of the error exceeding more than 1 mm in the 3-laser system vs. the 3-D SIS was shown to be 81.82% vs. 36.36% on the X-axis, 81.82% vs. 45.45% on the Y-axis, and 86.36% vs. 72.73% on the Z-axis. As a result, the 3-D SIS also exhibited a lower probability of setup error for the cancer patients. Therefore, this study confirmed that the 3-D SIS is a promising method for setup verification.