Set-up error validation with EPID images: Measurements vs Egs_cbct simulation

AimIn this study, the egs_cbct code’s ability to replicate an electronic portal imaging device (EPID) is explored.BackgroundWe have investigated head and neck (H&N) setup verification on an Elekta Precise linear accelerator. It is equipped with an electronic portal imaging device (EPID) that can capture a set of projection images over different gantry angles.Methods and materialsCone-beam computed tomography (CBCT) images were reconstructed from projection images of two different setup scenarios. Projections of an Anthropomorphic Rando head phantom were also simulated by using the egs_cbct Monte Carlo code for comparison with the measured projections.Afterwards, CBCT images were reconstructed from this data. Image quality was evaluated against a metric defined as the image acquisition interval (IAI). It determines the number of projection images to be used for CBCT image reconstruction.ResultsFrom this results it was established that phantom shifts could be determined within 2 mm and rotations within one degree accuracy using only 20 projection images (IAI = 10 degrees). Similar results were obtained with the simulated data.ConclusionIn this study it is demonstrated that a head and neck setup can be verified using substantially fewer projection images. Bony landmarks and air cavities could still be observed in the reconstructed Rando head phantom. The egs_cbct code can be used as a tool to investigate setup errors without tedious measurements with an EPID system

Development Of An Improved Wood’S Alloy End-Frame Casting Unit For Electron Field Shaping In Radiotherapy

Journal ArticleAs the second leading cause of death, cancer is a harsh reality. Skin cancer is one of the most prevalent cancers in South Africa and is commonly treated using electron radiation in radiotherapy. The applied radiation field needs to be shaped to the size of the cancer-affected area on the patient. This can be achieved through end-frames that fit into applicators that attach to the treatment unit. The end-frames are produced by casting Wood’s alloy into commercially available jigs. However, producing these end-frames presents various shortcomings such as lack of dimensional accuracy, the inconsistent density of the castings and the high cost of the jigs. The aim of this study was to develop a Wood’s alloy casting unit that can be made available to local oncology departments to produce endframes that are superior to what can be produced through commercial jigs. This paper describes the development and manufacturing of the new casting equipment and experiments performed to evaluate end-frames produced. Results showed that end-frames cast in the newly developed casting equipment are dimensionally more accurate, have consistent high density, and can be produced in a shorter time