No abstract

This paper presents the preliminary results of PET system simulation using Monte Carlo code. We also present the implementation of attenuation correction for MCNP-generated PET image. Using MCNP5 we constructed a data base for a uniform cylindrical source. The data obtained from the simulation were then used for PET image reconstruction. During the image reconstruction, calculated attenuation correction method was implemented to the PET raw data. This method was chosen due to the fact that our study involved homogeneous and simple geometry phantom.

Numerous methods have been introduced to segment the thyroid tumors in iodine-124 (124I) Positron Emission Tomography/Computer Tomography (PET/CT) imaging. An adaptive threshold-based is preferable to a manual and fixed threshold-based approach for forecasting accurate and precise tumor volume in real-patient studies, as it was reported to be more resistant to noise and resolution. Manual segmentation was reported to be time-consuming, subjective, subject to inter- and intra-observer variability and prone to segmentation errors [1]. This study aimed to determine the optimal adaptive threshold for thyroid tumor segmentation in 124I PET/CT imaging.   The objective of this study was firstly to determine the segmented volume using the standardized uptake value threshold method. Secondly, to compare the adaptive threshold and recovery coefficient (RC) value between the time of flight (TOF) and non-time of flight (non-TOF) PET/CT reconstructions in 124I phantom studies. Finally, to determine the accuracy and RC for 124I PET/CT studies. This study was done by placing NEMA 2012/IEC 2008 PET IQ Phantom and filled with 1 kBq/ml and 20 kBq/ml in its background and sphere each to model tumor background ratio (TBR) 20:1 of 124I PET/CT imaging. The phantom was scanned using TOF and non-TOF PET at 3, 4 and 5 minutes per bed position and reconstructed using 600, 1200 and 2000 beta penalization factors. Image registration, contouring and segmentation were performed using MIM Encore Software. A set of different adaptive thresholds (Tadaptive: 10%-50%) was applied to each sphere in the TBR image of the phantom using the tri-dimensional automatic segmentation tool. The optimal Tadaptive for each of the parameter assessed was defined based on the lowest goodness value calculated. The RC was calculated using mean value and known activity. Finally, the RC against the percentage of maximum was plotted to analyse the descending order of beta penalization factors for time per bed position.   Figure 1 shows the image of 124I contoured VOIs on the spheres. The results showed that segmented volumes were not affected by the time per bed position in 124I PET/CT imaging. Table 1 shows the descending order beta penalization factors for time per bed position. Beta penalization factors of 600 to 2000 resulted in either underestimation or overestimation of the measured volume. Comparing TOF to non-TOF PET/CT 124I imaging, consistent and reproducible data were observed for the TOF PET for the three beta penalization factors. Tadaptive of 28.0% consistently gave the lowest goodness value shown by the closest R2 value to one, thus can produce lowest error if it is being used to reconstruct images. As a conclusion, 28% Tadaptive is suggested as the optimal threshold for 124I TOF PET/CT imaging due to consistent data obtained for all beta penalization factors assessed in this study. The inconsistent data obtained by non-TOF PET thus requires further optimization.

The aim of this study is to study the effects of non –homogenous region closer to the HDR Brachytherapy source. Radial widths of 1, 3 and 5 cm of an inhomogeneous cylindrical area filled with bone and lung tissue in a water phantom are modelled in this study. The effects of this inhomogeneity to the g(r) and F(r,θ) of Nucletron 192Ir microSelectron HDR source are assessed. The results show that the assumption of homogeneous water leads to underestimation of the bone dose by the treatment planning system. Meanwhile, overestimation of the dose is observed in the surrounding area. A relative difference of up to 19% is calculated for the largest bone volume. Contrast results are observed for the lung inhomogeneity model. A relative difference of up to 12% is observed in the lung dose. The presence of inhomogeneous region in the water phantom affects the anisotropy function; at a radial distance greater than 5 cm. Our results indicate that the presence of bone and lung inside the water phantom affect the g(r) and F(r,θ) in HDR brachytherapy. The degree of the effects depends on the material, position and volume of the inhomogeneity area.

This research was conducted to evaluate scatter distribution at an X-ray room for diagnostic radiography using the Particle and Heavy Ion Transport code System (PHITS). The X-ray room was simulated using PHITS code based on the imaging room distance and length, as well as the control console room. The exact dimensions of the rooms were used as a geometry code in PHITS to simulate a point source isotopically with 100 keV energy in the X-ray room. There are three sources situated for this study which are source directed to the imaging table, inpatient bed, and Erect Bucky. Results show that PHITS simulation and measurement have a comparable value. The control console room is considered a safe place, based on the activation source from the simulation and measurement of the experimental dose with a dose ranged from 0.0540 to 0.1090 µSv per exposure. The control room is safe to the operator unless the number of cases handled is less than 11,086 cases per year. Comparison of dose distribution based on certain points of measurement and track detection from the simulation showed an approximate result. The dose obtained from the simulation and measurement is within the dose limits recommended by ICRP-60.