Comparison of 3DCBCT and 4DCBCT matching results in setup error assessment and correction for breast irradiation after breast-conserving surgery

Abstract

Objective To compare the differences in setup error (SE) assessment and correction between three-dimensional cone-beam computed tomography (3DCBCT) and four-dimensional CBCT (4DCBCT) in breast irradiation patients during free breathing after breast-conserving surgery. Methods Twenty patients with breast cancer after breast-conserving surgery were recruited for external beam breast irradiation and 4DCBCT and 3DCBCT simulation. The target volumes were delineated. Volumetric modulated arc therapy plans were designed using the MONACO v5.10 treatment planning system. 3DCBCT and 4DCBCT images were collected alternately five times each before breast irradiation. The CT images were matched, and the interfraction SEs were acquired. After online setup correction, the residual errors were calculated, and the SEs, systematic errors, and random errors were compared. The paired t test was used for comparison between groups. Results The SEs acquired by 4DCBCT were significantly larger than those acquired by 3DCBCT in three directions (P=0.035, 0.018, 0.040). After online setup correction, the random errors based on 3DCBCT were significantly smaller than those based on 4DCBCT in left-right and anterior-posterior (AP) directions (0.5±0.39 mm vs. 0.7±0.30 mm, P=0.005; 0.9±1.09 mm vs. 1.2±0.48 mm, P=0.000), and the residual errors based on 3DCBCT were also significantly smaller than those based on 4DCBCT in AP direction (0.2±0.33 mm vs. 0.6±0.63 mm, P=0.000). The setup margins based on 4DCBCT was significantly larger than those based on 3DCBCT in AP direction both before and after online setup correction (P=0.002). Conclusions Compared with 3DCBCT, 4DCBCT has more advantages in monitoring the SEs in three directions. Both 3DCBCT and 4DCBCT have similar efficacy in random error correction. The satisfying position repeatability and minimized target volume margins will be achieved by online setup correction. Key words: Tomography, X-ray computed, cone beam; Breast neoplasms/radiotherapy; Setup error