Figure 3.

Distribution of measured gap errors for six patients treated with supine technique. Measurements done after planned couch shifts with BB placement described in Section II: a) gap 1: $\text{mean error}=1.0\hspace{0.17em}\text{mm}\hspace{0.17em}(\sigma =1.3\hspace{0.17em}\text{mm}$); b) gap 2: $\text{mean error}\hspace{0.17em}=\hspace{0.17em}1.6\hspace{0.17em}\text{mm}\hspace{0.17em}(\sigma =2.1\hspace{0.17em}\text{mm}$).