Fig. 6

Images showing intra-fraction displacement. The pre (a, c, e) and post-treatment (b, d, f) CBCT scans for 3 patients are displayed. In patient 1′s pre-treatment a the superior clip in within the prostate bed PTV (red volume) but on the post-treatment b the bladder had continued to fill by a small amount and caused the prostate bed and superior clip to move posterior and superior causing a marginal miss. Patient 2’s pre-treatment c had little rectal gas present but on the post-treatment d a large amount of gas appeared in the prostate bed region which caused the prostate bed to move anteriorly resulting in a marginal miss. The third patient’s pre-treatment e showed relaxed buttock check and in the post-treatment f the left buttocks cheek had tensed after the bladder continued to fill and caused the prostate bed to move laterally