Abstract
Accurate patient positioning is extremely important in radiation therapy for head-and-neck cancer. With the introduction of three-dimensional cone beam computed tomography (CBCT) at the Wellington Blood and Cancer Centre (WBCC), it was agreed that positioning accuracy required improvement. This led to the establishment of a multidisciplinary team (MDT) focused on patient positioning. Following a number of process changes made by the MDT, improvements in setup accuracy were observed but not formally quantified.
The aim of this thesis was to retrospectively quantify setup accuracy at WBCC, using CBCT images of 96 patients treated for head-and-neck cancer. On average 7 CBCT scans per patient were sequentially registered using each of the following match structures: C1-C3, C3-C5, C5-C7, C7-caudal, mandible occipital bone and the larynx. This enabled quantification of patient deformation as the measure of setup accuracy, by calculating the position of each structure relative to C1-C3. Statistical Process Control (SPC) was then used to assess trends in setup accuracy over time, allowing identification of specific time points where improvements occurred and correlation with process changes to be made.
The multiple rigid registration protocol and deformation values calculated for this patient cohort clearly demonstrated the relative movement of anatomical sub regions in the head-and-neck. SPC charts showed that a significant and consistent reduction in deformation was achieved since the instigation of the MDT. A reduction in the magnitude and variation of the patient systematic 3D-deformation vector was observed, from 2.8 mm ± 0.1 mm (1 S.D.) in 2011 to 0.9 ± 0.0 mm (1 S.D.) in late 2013/early 2014. Statistical correlation analysis revealed that the introduction of new head supports (p = 0.003), as well as retraining of staff in making immobilisation equipment (p = 0.003) had a significant impact on patient systematic deformation. Both of these changes were actions initiated by the multidisciplinary team, which shows that a multidisciplinary approach to patient positioning had a positive impact on setup accuracy in our department.