Use In Radiotherapy Treatment Research Articles

The impact of smart metal artefact reduction algorithm for use in radiotherapy treatment planning.

The presence of metal artefacts in computed tomography (CT) create issues in radiation oncology. The loss of anatomical information and incorrect Hounsfield unit (HU) values produce inaccuracies in dose calculations, providing suboptimal patient treatment. Metal artefact reduction (MAR) algorithms were developed to combat these problems. This study provides a qualitative and quantitative analysis of the "Smart MAR" software (General Electric Healthcare, Chicago, IL, USA), determining its usefulness in a clinical setting. A detailed analysis was conducted using both patient and phantom data, noting any improvements in HU values and dosimetry with the GE-MAR enabled. This study indicates qualitative improvements in severity of the streak artefacts produced by metals, allowing for easier patient contouring. Furthermore, the GE-MAR managed to recover previously lost anatomical information. Additionally, phantom data showed an improvement in HU value with GE-MAR correction, producing more accurate point dose calculations in the treatment planning system. Overall, the GE-MAR is a useful tool and is suitable for clinical environments.

Evaluation of MRI Distortion Correction for Use in Radiotherapy Treatment Planning

Aims: The aim of this work was to investigate the distortion correction feature of a dedicated Siemens Espree 1.5T MRI scanner for use in radiotherapy treatment planning. This application of MRI requires a high degree of spatial accuracy to allow fusion of CT and MRI images to improve tumour delineation. Commercially available phantoms did not satisfy requirements as they did not allow testing over a sufficiently large field of view, and needed repositioning between scans to image different planes.

Evidence-based estimation and radiotherapy utilisation rate in Andalusia

The objective of this study was to estimate the theoretical needs -based on evidence- of radiotherapy treatments (RDT) in Andalusia, compare these needs with actual use of RDT in 2006 and analyse their evolution from 2003. Correlation between quantitative variables was analysed with Pearson's correlation coefficient. This dealt with differences between administered/estimated treatments and treatments carried out in years with the Student's t-distribution, and the Xi2 test among qualitative variables. In Andalusia, the evidence-based rate of cancer irradiation is 55%. Eighty-five percent of theoretical treatments were administered in 2006. From this group, 107% were in gynaecological tumours, 100% in breast cancer cases, 71% in head and neck cancer and 48% in lung cancers; differences in the last two conditions were significant (p<0.01). As for regional distribution, differences were reported with reference to irradiation rates (p<0.0002) and resource distribution. In the last three years, an increment of 17% was observed in treatments conducted in public hospitals. The rate increased from 61% (with regard to optimal values) to 85% in 2006; in a parallel way, an increment was seen in therapy units (from 22 to 26) and radiation oncologists (from 57 to 69). Despite the increment of irradiation rates seen in the last years, there is still a serious underutilisation of RDT for some cancer types (lung, head and neck cancer), as well as a great variability in the use of RDT between hospitals.

649 poster Automated brain segmentation method for FMRI and it's use in radiotherapy treatment planning

649 poster Automated brain segmentation method for FMRI and it's use in radiotherapy treatment planning

Analysis and correction of geometric distortions in 1.5 T magnetic resonance images for use in radiotherapy treatment planning

The aim of this study is to investigate and correct for machine- and object-related distortions in magnetic resonance images for use in radiotherapy treatment planning. Patients with brain tumours underwent magnetic resonance imaging (MRI) in the radiotherapy position with the head fixed by a plastic cast in a Perspex localization frame. The imaging experiments were performed on a 1.5 T whole body MRI scanner with 3 mT m-1 maximum gradient capability. Image distortions, caused by static magnetic field inhomogeneity, were studied by varying the direction of the read-out gradient. For purposes of accuracy assessment, external and internal landmarks were indicated. Tubes attached to the cast and in the localization frame served as external landmarks. In the midsagittal plane the brain-sinus sphenoidalis interface, the pituitary gland-sinus sphenoidalis interface, the sphenoid bone and the corpora of the cervical vertebra served as internal landmarks. Landmark displacements as observed in the reversed read-out gradient experiments were analysed with respect to the contributions of machine-related static magnetic field inhomogeneity and susceptibility and chemical shift artifacts. The machine-related static magnetic field inhomogeneity in the midsagittal plane was determined from measurements on a grid phantom. Distortions due to chemical shift effects were estimated for bone marrow containing structures such as the sphenoid bone and the corpora of the cervical vertebra using the values obtained from the literature. Susceptibility-induced magnetic field perturbations are caused by the patient and the localization frame. Magnetic field perturbations were calculated for a typical patient dataset. The midsagittal head image was converted into a susceptibility distribution by segmenting the image into water-equivalent tissues and air; also the Perspex localization frame was included in the susceptibility distribution. Given the susceptibility distribution, the magnetic field was calculated by numerically solving the Maxwell equations for a magnetostatic field. Results were shown as magnetic field perturbations and corresponding spatial distortions of internal and external landmarks. The midsagittal head images were corrected for the machine imperfections (gradient non-linearity and static magnetic field inhomogeneity). The locations of the external landmarks in the frame were also corrected for susceptibility artifacts. The efficacy of the corrections was evaluated for these external landmarks in the localization frame with known geometry. In this study at 1.5 T with read-out gradient strength of 3 mT m-1, machine-related, chemical shift and susceptibility-induced static magnetic held inhomogeneity were of the same order, resulting in spatial distortions between -2 and 2 mm with only negative values for the chemical shift effect. Both the patient and the localization frame proved to perturb the magnetic field. The field perturbations were shown to be additive. In total, static magnetic field inhomogeneity led to spatial distortions ranging from -2 to 4 mm in the direction of the read-out gradient. Non-linearity of the gradients resulted in spatial distortions ranging from -3.5 to 0.5 mm. After correction for the machine imperfections and susceptibility artifacts, the geometric accuracy of the landmarks in the localization frame was better than 1.3 mm.

The relation between x-ray CT numbers and charged particle stopping powers and its significance for radiotherapy treatment planning

The theoretical results for CT number and relative stopping power given appear to be very reliable, except possibly when large components of high Z elements are present. This implies that the calibration curve given could be used to convert measured CT numbers to relative stopping powers for use in radiotherapy treatment planning for charged particles, such as protons, heavy ions and negative pions, particularly in regions where experimental data are not available. As materials which are tissue-equivalent for electrons and x-rays are not tissue-equivalent for pions (Lewis et al., 1982), it may be more reliable to use theoretical results for real tissues, rather than experimental results for the tissue substitutes in common use.