Figure 2.

IsoCal results for three independent calibrations in a row for five linacs: the lateral (X) and longitudinal (Y) offsets in a full gantry rotation between the MV ((a) to (c)) and kV imager centers ((b) and (d)) (the origin) and the projected treatment isocenter. ${\mathrm{X}}_1$ ${\mathrm{X}}_2$, ${\mathrm{Y}}_1$ and ${\mathrm{Y}}_2$ are the points in each direction with the extreme values in that direction as illustrated in (b) (first curve); these extreme values were used as a metric of IsoCal reproducibility, as presented in Table 1. (a) and (b) are the results for linac M1, in (c) and (d): M1, Green, M2: Orange; M3: Red; M4: Black; M5: Blue.

Table 1.

Maximum differences ($\delta {\mathrm{X}}_1$, $\delta {\mathrm{X}}_2$, $\delta {\mathrm{Y}}_1$, $\delta {\mathrm{Y}}_2$) in extreme values (mm) for MV and kV panel corrections in each direction for the three IsoCal determinations for the five linacs. Figure 2 shows the full data for M1 and the definitions of ${\mathrm{X}}_1$, ${\mathrm{X}}_2$, ${\mathrm{Y}}_1$, $\delta {\mathrm{Y}}_2$. All corrections are given in the plane of the isocenter

	MV				kV
	$\delta {\mathrm{X}}_1$	$\delta {\mathrm{X}}_2$	$\delta {\mathrm{Y}}_1$	$\delta {\mathrm{Y}}_2$	$\delta {\mathrm{X}}_1$	$\delta {\mathrm{X}}_2$	$\delta {\mathrm{Y}}_1$	$\delta {\mathrm{Y}}_2$
M1	0.0	0.1	0.2	0.1	0.0	0.0	0.2	0.2
M2	0.1	0.1	0.1	0.1	0.1	0.1	0.2	0.1
M3	0.1	0.1	0.2	0.1	0.0	0.1	0.1	0.0
M4	0.0	0.0	0.1	0.1	‐0.1	0.0	0.1	0.1
M5	0.1	0.1	0.1	0.1	0.2	0.2	0.2	0.1