Session Item

This service evaluation project compared the IQ of dose optimised pelvic CBCT protocols, developed in house at Weston Park Cancer Centre, UK, based on work by Wood et al (2015), with that of the manufacturer’s (Varian) standard pelvis protocol.

20 patients receiving daily treatment verification imaging with CBCT as part of their radiotherapy for localised prostate cancer, were selected for inclusion in the service evaluation project.

Within the existing imaging schedule, the patients were scanned using the standard pelvis CBCT protocol for fractions one and two, and the dose optimised pelvis CBCT protocol was used for fractions three and four. For the remaining fractions the standard protocol was used. There was no additional radiation exposure to the patient than what was already set out within the agreed imaging protocols.

The IQ of the CBCTs was assessed by two independent observers. The Likert scale used in a study by Langmack, Newton, Jordan & Smith, (2016) was adapted and used to assess IQ:

3 = Excellent, no artefacts, 2 = Good, few artefacts, 1 = Poor, just about able to match.

Statistical analysis was performed to compare the IQ of the dose optimised and the standard pelvis CBCT protocols. 

No CBCT image, either standard protocol or dose optimised protocol, was deemed to be of too poor IQ to be used clinically.

Statistical analysis on the differences in the results of the two imaging protocols was performed using the paired t test and the Wilcoxon signed rank test. 

Both tests returned p values of 0.8 -a p value of <0.05 is required to show statistical significance.  Therefore there was not enough evidence to prove that the CBCT protocols gave different IQ results.

Kappa tests gave results close to zero, implying no better than random agreement between the raters.

The dose optimised CBCT protocols developed at Weston Park Cancer Centre provide images that are of suitable quality for their intended clinical purpose, and can safely be rolled out into clinical practice. 

References

1.      Wood, T., Moore, C., Horsfield, C., Saunderson, J., & Beavis, A. (2015).

Accounting for patient size in the optimization of dose and image quality of pelvis cone beam CT protocols on the Varian OBI system.

British Journal of Radiology, 88(1055).

2.      Langmack, K. A., Newton, L. A., Jordan, S., & Smith, R. (2016).

Cone beam CT dose reduction in prostate radiotherapy using Likert scale methods. 

The British Journal of Radiology, 89(1059), 20150460. doi:10.1259/bjr.20150460