Noor Diyana Osman

Monte carlo dose calculation in dental amalgam phantom

It has become a great challenge in the modern radiation treatment to ensure the accuracy of treatment delivery in electron beam therapy. Tissue inhomogeneity has become one of the factors for accurate dose calculation, and this requires complex algorithm calculation like Monte Carlo (MC). On the other hand, computed tomography (CT) images used in treatment planning system need to be trustful as they are the input in radiotherapy treatment. However, with the presence of metal amalgam in treatment volume, the CT images input showed prominent streak artefact, thus, contributed sources of error. Hence, metal amalgam phantom often creates streak artifacts, which cause an error in the dose calculation. Thus, a streak artifact reduction technique was applied to correct the images, and as a result, better images were observed in terms of structure delineation and density assigning. Furthermore, the amalgam density data were corrected to provide amalgam voxel with accurate density value. As for the errors of dose uncertainties due to metal amalgam, they were reduced from 46% to as low as 2% at d80 (depth of the 80% dose beyond Zmax) using the presented strategies. Considering the number of vital and radiosensitive organs in the head and the neck regions, this correction strategy is suggested in reducing calculation uncertainties through MC calculation.

Examination Two: Questions

Q1. The technique used to minimise motion blur includes: n n nA. Increasing the mA n n nB. Increasing the exposure time n n nC. Using a fast film-screen combination n n nD. Image magnification n n nE. Using a breath-hold technique

Examination Eight: Questions

Q1. Regarding the photographic emulsion of radiographic film: n n nA. It is made of silver halide crystals. n n nB. The emulsion layer is coated onto a base material. n n nC. The thickness of the emulsion is 1 mm. n n nD. It is sensitive to radiation. n n nE. It is sensitive to visible light.

Examination Seven; Questions

Q1. Regarding modulation transfer function (MTF): n n nA. It describes the image contrast of an imaging system. n n nB. It is based on Fourier analysis. n n nC. The MTF value increases with better visibility of small structures. n n nD. The MTF curve is specific to an imaging system. n n nE. The MTF value is not applicable for a digital system.

Examination Four: Questions

Q1. Regarding image receptor in digital radiography: n n nA. The image receptor is divided into a matrix of pixels. n n nB. Increasing the number of pixels reduces the spatial resolution. n n nC. Fill factor is the percentage of pixel area that is sensitive to radiation. n n nD. Signal in pixel array is read out using the associated electronic circuitry. n n nE. Each pixel contains a photoconductor.

Examination Five: Questions

Q1. Regarding display and post-processing of digital radiographic images: n n nA. Liquid crystal display (LCD) monitor utilises variation in light polarisation within the crystal for image visualisation. n n nB. The LCD monitor has to be calibrated to the DICOM standard to display images for primary diagnostic clinical interpretation n n nC. The size of a good quality digital image is over 10 megabytes of data. n n nD. Windowing improves spatial resolution. n n nE. Averaging a few images reduces the noise.

Examination One: Questions

Q1. Regarding digital radiographic image n n nA. A larger pixel size is required for a larger field of view if the number of pixels is the same n n nB. Increasing the pixel size increases the spatial resolution n n nC. The bit depth determines the number of greyscale range of a pixel n n nD. A 12-bit pixel stores up to 512 levels of grey n n nE. Lossless compression of an image causes degradation of the image quality

Examination Six: Questions

Q1. Picture archiving and communications system (PACS): n n nA. Stores digital radiographic images in DICOM format n n nB. Removes the need for film storage n n nC. Cannot be accessed from different locations simultaneously n n nD. Compresses the stored images to help reduce the storage requirement n n nE. Use Health Level Seven (HL7) standard

Examination Three: Questions

Q1. Overall detection efficiency of a detector in nuclear medicine department is affected by: n n nA. Quantum detection efficiency n n nB. Intrinsic efficiency n n nC. Photopeak efficiency n n nD. Geometric design of the detector n n nE. Distance of the source from the detector

Examination Nine: Questions

Q1. Optical density is: n n nA. The ratio of incident light to transmitted light in logarithmic form n n nB. Measured using densitometer n n nC. A measure of the degree of film darkening n n nD. Referred as radiographic density n n nE. 1.0 if 100% of the incident light is transmitted