Analysing the integration of MR images acquired in a non-radiotherapy treatment position into the radiotherapy workflow using deformable and rigid registration.

Abstract

Our aim was to analyse the feasibility of integrating an MRI acquired in a non-radiotherapy set-up into the prostate cancer radiotherapy workflow. The MRIs of 15 prostate cancer patients, acquired with a flat table-top (MRI-flat), and with a curved tabletop (MRI-curve) were analysed. MRIs were rigidly (RIR) and non-rigidly registered (DIR) with CT images. The prostate and rectum were contoured in each image set and translated to the CT, and IMRT plans were computed taking into account structural changes after RIR and DIR (P-flatRIR, P-curveRIR and P-curveDIR). In addition the P-curveDIR was overlaid with RIR structures. Spatial overlap parameters and dose-volume histogram metrics were generated. No significant differences were observed among P-flatRIR and P-curveRIR or P-flatRIR and P-curveDIR. Median gamma-values: P-curveRIR, 95.3%; P-curveDIR, 96%, translated-P-curveDIR, 95%. DVH metrics for translated-P-curveDIR were: Dmin, 64.5Gy; Dmean, 70.06Gy; V95%, 100%. No statistically significant differences were found in the dosimetric MRI-flatDIR values. The dosimetric reproduction of treatment position image following image registration of non-radiotherapy set-up images suggests that it is feasible to integrate these images into the radiotherapy workflow.