Figure 2

Percentage of the total fractions outside the margins, for margins from 1 to 8 mm. The data (all the fractions, all the patients) are computed by using the absolute values of the shifts given by the T-match. Dotted-dashed lines show the results if no correction is made on patient position. Solid lines show the results of a simulated off-line protocol based on the first 5 CBCTs. The area in grey represent the 5% and 95% confidence levels. Dashed lines show the results if a daily correction is made on the basis of daily CBCT. For the antero-posterior (Z) axis the percentages are divided into two cases, Z positive and Z negative, because there is no symmetry in the margins we apply for the positive and negative directions. The vertical lines are positioned at the margins currently used.