Are cone beam CT image matching skills transferrable from planning CT to planning MRI for MR-only prostate radiotherapy?

Abstract

Objectives: Treatment verification for MR-only planning has focused on fiducial marker matching, however, these are difficult to identify on MR. An alternative is using the MRI for soft-tissue matching with cone beam computed tomography images (MR-CBCT). However, therapeutic radiographers have limited experience of MRI. This study aimed to assess transferability of therapeutic radiographers CT-CBCT prostate image matching skills to MR-CBCT image matching. Methods: 23 therapeutic radiographers with 3 months–5 years’ experience of online daily CT-CBCT soft-tissue matching prostate cancer patients participated. Each observer completed a baseline assessment of 10 CT-CBCT prostate soft-tissue image matches, followed by 10 MR-CBCT prostate soft-tissue image match assessment. A MRI anatomy training intervention was delivered and the 10 MR-CBCT prostate soft-tissue image match assessment was repeated. Limits of agreement were calculated as the disagreement of the observers with mean of all observers. Results: Limits of agreement at CT-CBCT baseline were 2.8 mm, 2.8 mm, 0.7 mm (vertical, longitudinal, lateral). MR-CBCT matches prior to training were 3.3 mm, 3.1 mm, 0.9 mm, and after training 2.6 mm, 2.4 mm, 1.1 mm (vertical, longitudinal, lateral). Results show similar limits of agreement across the assessments, and variation reduced following the training intervention. Conclusion: This suggests therapeutic radiographers’ prostate CBCT image matching skills are transferrable to a MRI planning scan, since MR-CBCT matching has comparable observer variation to CT-CBCT matching. Advances in knowledge: This is the first publication assessing interobserver MR-CBCT prostate soft tissue matching in an MR-only pathway.

Images and images: Current roles of therapeutic radiographers

“…A single centre study has demonstrated that TRs can competently match MR-CBCT with comparable results to CT-CBCT. 56 The transferable skills identified here, and the potential of this data is very promising and will hopefully propel more centres to trial this and assess their TRs.…”

Cone beam computed tomography image guidance within a magnetic resonance imaging-only planning workflow

“…Brooks et al indicated that the application of a training package resulted in a lower inter-observer variability in MRI-CBCT matching than without [20] . Due to the lack of pre-post testing in this study, it is difficult to determine in this study if the training package similarly affected the inter-observer variability in the MRI-CBCT matching.…”

“…An MRI image matching training package was developed by two MRI trained radiation therapists, based on a previously successful training model [20] . The training package comprised of basic MRI tissue weightings, MRI anatomy of the pelvis in males and females, identification of key anatomical features on T1 and T2-weighted MRI, and the rationale behind MRI matching for MRI-only planning workflows.…”

“…Two studies, which focused on MRI-CBCT image guidance, have assessed the soft tissue match accuracy for prostate treatments, while another study focused on anal canal and rectum, utilising only one matcher with automatic registration [17] , [18] , [19] . While the results of these studies appear promising, additional work on this topic has identified that a training package reduces the inter-observer variability in MRI-CBCT matching, to align with the variability of CT-CBCT matching values [20] .…”