BACKGROUND: To compare setup errors and clinical target volume (CTV)-to-planning target volume (PTV) margins of three-dimensional cone beam computed tomography (3D CBCT) versus four-dimensional cone beam computed tomography (4D CBCT) based image-guided radiation therapy for liver cancer, and to evaluate the advantages of 4D CBCT in position verification. METHODS: From January 2021 to June 2022, patients with clinically or pathologically confirmed primary liver cancer scheduled for radiotherapy of intrahepatic lesions were prospectively enrolled. All patients underwent simulation using computed tomography and magnetic resonance. The target delineation and treatment planning were performed in the Pinnacle system. Image guidance for radiotherapy involved two sequential scans, with a 3D CBCT scan and a 4D CBCT scan. All CBCT images were registered with the planning CT and six-degrees-of-freedom setup errors were assessed. Linear mixed-effects models with random intercepts for patients and fractions nested within patients were used to evaluate differences in setup errors between 3D and 4D CBCT. Estimated marginal means were used for pairwise comparisons between modalities. The couch registration was based on the 4D CBCT. CTV-to-PTV margins were calculated using van Herk's formula and compared using the Wilcoxon test. RESULTS: Totally, 55 patients were enrolled, yielding 445 paired 3D CBCT and 4D CBCT images. The estimated marginal means (3D CBCT vs. 4D CBCT) were as follows: left-right direction (L-R), 0.033 vs. 0.033 cm (p = 0.994); superior-inferior direction (S-I), - 0.089 vs. 0.123 cm (p < 0.001); and anterior-posterior direction (A-P), 0.043 vs. 0.086 cm (p < 0.001). For rotational errors, no significant difference was observed in Rx (sagittal), 0.313° vs. 0.283° (p = 0.480), whereas significant differences were found in Ry (transverse), 0.622° vs. 0.978° (p < 0.001), and Rz (coronal), - 0.025° vs. 0.231° (p < 0.001). Calculated CTV-to-PTV margins in L-R, S-I, and A-P directions were 0.57, 0.98, and 0.58 cm for 3D CBCT and 0.51, 0.80, and 0.46 cm for 4D CBCT, respectively. CONCLUSIONS: 4D CBCT demonstrates superior setup accuracy and enables reduced CTV-to-PTV margins, supporting its use as the preferred image-guidance modality in liver cancer radiotherapy. CLINICAL TRIAL NUMBER: Not applicable.
Wan et al. (Mon,) studied this question.