Fig. 2

Box and whisker plots of the 3D-SS test performed using Varian and Elekta machines at 22 institutions (bold line, median; cross, mean; boxes, first and third quartiles; whiskers, 5th and 95th percentiles; circles, outliers). (A) Minimum distance (\(\:{d}_{\text{m}\text{i}\text{n}}\)) of the seven beams from the imaging isocenter in three directions. (B) Value of \(\:{d}_{\text{m}\text{i}\text{n}}\) for the seven beams, expressed in terms of the resultant vector. (C) Distance between the imaging isocenter and radiation isocenter (\(\:{d}_{\text{i}\text{I}\text{C}-\text{r}\text{I}\text{C}}\)) in three directions. (D) Value of \(\:{d}_{\text{i}\text{I}\text{C}-\text{r}\text{I}\text{C}}\) expressed in terms of the resultant vector. (E) Radius (\(\:r\)) of the smallest sphere that intersects all radiation beams. Notation: n.s. = not significant; *p < 0.05; **p < 0.01; ***p < 0.001. The positive and negative symbols on \(\:{d}_{\text{m}\text{i}\text{n}}\) and \(\:{d}_{\text{i}\text{I}\text{C}-\text{r}\text{I}\text{C}}\) indicate directions in DICOM reference coordinate systems.