Fig. 3

The illustration of three pairs of CBCT to planning CT registration. a shows F-CBCT to planning CT registrations (upper) and D-CBCT to planning CT registration (lower) of a head phantom. The translation differences were − 0.2 mm, − 0.1 mm and − 0.2 mm for x, y and z directions, respectively. The rotational differences were 0.1°, − 0.1°and − 0.1°for x, y and z directions, respectively. b shows F-CBCT to planning CT registrations (upper), and D-CBCT to planning CT registration of a typical case 1 (lower). The translation differences were − 0.2 mm, 0.2 mm and − 0.3 mm for x, y and z directions, respectively. The rotational differences were 0.2°, − 0.1°and − 0.0°for x, y and z directions, respectively. The registration result of case 1 was close to the average performance among 62 cases. c shows F-CBCT to planning CT registrations (upper) and D-CBCT to planning CT registration (lower) of a typical case 2. The translation differences were 0.4 mm, − 0.1 mm and − 1.8 mm for x, y and z directions, respectively. The rotational differences were − 0.1°, − 0.3°and − 0.2°for x, y and z directions, respectively. The registration difference of case 2 was the maximum among 62 cases