Computed tomography-magnetic resonance image registration in radiotherapy treatment planning.

Magnetic resonance imaging (MRI) is being increasingly used in radiotherapy treatment planning (RTP). MRI has the potential to provide improved localisation of target volumes, leading to better tumour control rates and reduced normal tissue complications, due to capabilities including excellent soft-tissue discrimination and the ability to provide scans in which the image contrast is weighted according to different tissue properties. When computed tomography (CT)-MRI image registration is deployed, MR's advantages are combined with CT's geometrical security and its ability to provide electron density information. The quality of CT-MRI image registration can be favourably influenced by aspects of scan acquisition, including patient positioning/immobilisation and scan protocols. Appropriate protocols can ameliorate the possible presence of MR spatial distortions and other artefacts, but quality assurance of scanning remains essential. Here, the methods and quality assurance of CT-MR image registration are discussed. Developments in MRI scanner technology are progressively offering advantages for RTP, in terms of the possibility of better matching of patient positioning versus CT in a greater range of anatomical regions, while allowing thinner slices for better image quality in reformatted orthogonal planes.

MRI image-based FE modelling of the pelvis system and bladder filling.

In this study, high-resolution magnetic resonance imaging was performed in the transaxial, coronal and sagittal planes to provide comprehensive structural details of the bladder and surrounding systems. Detailed finite-element (FE) models that were specific to each participant were developed by rendering the images, and the process of bladder filling was simulated. The overall model of bladder deformation was compared with repeated images of the filled bladder that were obtained using computed tomography to validate the FE models. The relationship between the changes in the key dimensions of the bladder and the increase in bladder volume during the filling process was also investigated. The numerical results showed that the bladder dimensions increased linearly with its volume during the filling process and the predicted coefficients are comparable to some of the published clinical results.

Monte Carlo simulation and polymer gel dosimetry of 60 MeV clinical proton beams for the treatment of ocular tumours.

Monte Carlo (MCNPX) simulations of a clinical proton beam-line under a range of beam conditions have been compared with MR analysis of irradiated polymer gel (BANG-1). Gel results were found to under-estimate the height of the full energy Bragg peak relative to simulation by the order of 30%, due to increased LET in this region, which has been reported elsewhere. Comparison of narrow-beam lateral profiles suggests a slight over-prediction of lateral proton scatter in MCNPX, which has been reported previously.