Table 1 Overview of the HU accuracy evaluation in terms of mean absolute error (MAE) and mean error (ME) in the test set. The results are presented as mean ± 1σ and the range ([min; max]) for the whole breast CTV and CBCT-ROI

15 ± 3 [12;24]

2 ± 4 [−9;9]

32 ± 7 [23;51]

1 ± 8 [−18;23]

80 ± 25 [35;169]

73 ± 29* [15;167]

142 ± 21 [107;198]

18 ± 42 [−69;130]

50 ± 13 [29;81]

3 ± 8 [−19;22]

66 ± 9 [50;84]

2 ± 9 [−15;26]

35 ± 15 [17;75]

−7 ± 28 [−72;57]

61 ± 13 [42;110]

−18 ± 25 [−79;28]

19 ± 6 [12;42]

3 ± 5 [−10;15]

48 ± 6 [35;68]

−3 ± 9 [−24;27]