Fig. 1

Histogram displaying the frequency of fractions with bad to good alignment of delineated structures: Number of fractions with volumes of interest (VOIs) that were improved in terms of an increased similarity value by the radiation therapists. Light (dark) grey colored bars indicate the improvement achieved by expert correction in respect to the laser-based (bony-based) positioning = expert-IGRT vs. non-IGRT (= expert-IGRT vs. bone-IGRT). The x-axis of the histogram describes the fraction of VOIs per patient (e.g. 50–60% interval holds the number of fractions, where the expert correction achieved an improvement in 50–60% of all delineated VOIs of the corresponding patient). The numbers above the bars resemble the height of the bar for better comparison. The fraction number Fi framed in the upper part of the graph indicates the median fraction number within the series in the corresponding dark grey bar (e.g. the dark grey bar with 50–60% of VOIs per patient experiencing a similarity improvement has the median fraction number F14)