ESTRO 2024 - Abstract Book

S5565

RTT - Patient care, preparation, immobilisation and IGRT verification protocols

ESTRO 2024

Table 1. shows Likert score results for duodenum and small bowel contouring.

Likert score

Duodenum (total scans=33)

Small bowel (total scans=30)

1: Unable to contour any small bowel or duodenum 6 2: Unsatisfactory: contours mostly approximated and high number of artefacts, able to contour some but not complete, or very low level of confidence in contours. 8 3: Adequate image quality: able to fully contour the organ but much is approximated. 4: Good image quality: can be outlined with only a few approximations, minimal artefacts. 8 5: Excellent image quality: easy to outline, comparable quality with planning CT scan. 0

7

16

11

6

1

0

For the duodenum, 19 scans out of 33 scored as either adequate or good. 14 were classed as unsatisfactory or below. This suggests that the visualisation of the duodenum may be consistent enough to use verification CBCTs to measure and quantify motion of the duodenum. The small bowel was more difficult to visualise and contour, with the majority of scans (23 out of 30) classed as unsatisfactory or unusable. Only six scans provided adequate contours and only one was deemed of good image quality. Therefore, these CBCTs cannot be used to accurately measure positional variation of the small bowel.

The results also suggested that both increased volumes of gas and increased patient separation may have an impact on image quality.