The linear and the mass attenuation coefficients of Rhizophora spp. wood in the photon energy range of 11.22 - 28.43 keV were determined. This was done by studying the attenuation of x-ray fluorescent (XRF) photons from selenium, molybdenum, silver and tin targets. Both the Kα and Kβ peaks were utilised. The results were compared with theoretical values for average breast tissues for youngage, middle-age and old-age groups calculated by using a XCOM computer programme. The mass attenuation coefficient of Rhizophora spp. was found to be close to that of the calculated young-age breast in this photon energy range.
Digital mammography has been progressively introduced in screening centers and the concern is to achieve an image of diagnostic value which would be able to detect early changes in the breast tissue. The aim of this study was to evaluate the image quality of mammograms using quantitative and qualitative methods of two FFDM systems with variations in breast thickness and anode/filter combination. This study was done from January to April 2008 with two FFDM systems; Siemens Mammomat NovationDR at Diagnostic Imaging Department, Hospital Kuala Lumpur and Hologic Lorad Selenia at Breast Clinic, National Cancer Society. A CIRS012A tissue equivalent breast phantom (4, 5 and 6 cm) thickness was used to obtain images in the craniocaudal plane with 26-32 kVp and a combination of molybdenum/molybdenum (Mo/Mo) and molybdenum/rhodium (Mo/Rh) anode/filter. For the qualitative evaluation, two independent radiologist with a minimum of five years experience was used to score the images. Wilcoxon Sign Rank Test showed that there are no significant differences (p > 0.05) in image quality between both the FFDM systems. Kappa analysis had a poor agreement between the scores given by the two radiologists. The quantitative analysis using Mann-Whitney test showed that there are significant differences (p < 0.05) between the SNR values of both FFDM systems. Although the qualitative evaluation was similar, the study showed that Lorad Selenia had a significantly superior SNR value, hence would be a better tool to detect early changes in the breast tissue. This study also demonstrated that a lower kVp is more suitable with molybdenum filter and as the breast thickness is increased rhodium filter with higher kVp displayed better quality images.
Mammography is used as a screening tool for early detection of breast cancer. However, the radiation dose used should be as low as possible to minimize any effects on asymptomatic woman while maintaining the diagnostic value of the image as mammography is done annually. This study was done to determine the optimum exposure parameter in exposure control mode (AEC) for two combinations of anode/filter which were molybdenum/molybdenum (Mo/Mo) and molybdenum/rhodium (Mo/Rh) using the Lorad Selenia digital mammography system at the Women’s Breast Clinic, National Cancer Society (NCS). A CIRS012A mammography research of phantom 4 cm thickness with 50% glandularity was exposed in the cranio-caudal projection. TLD 100H was used to measure the entrance surface air kerma (ESAK). The AGD values were then calculated from the ESAK values, incorporating three correction factors (g, c and s) according to Euref protocol. Image quality was evaluated using signal to noise ratio (SNR). Figure of Merit (FOM) which is the ratio of the square of SNR to the AGD shows that 30 kVp is the optimum exposure parameter for a 4 cm thickness phantom with the use of Mo/Rh and Mo/Mo anode/filter combination. Non-parametric Spearman correlation test showed a negative linear relationship between AGD and SNR with increasing tube voltage for both anode/filters.
Keywords: Average glandular dose; CIRS012A phantom; exposure; full field digital mammography
Study site: Women’s Breast Clinic, National Cancer Society (NCS), Kuala Lumpur, Malaysia
The geometry of reactor core, thermal column, collimator and shielding system for BNCT application of TRIGA MARK II REACTOR were simulated with MCNP5 code. Neutron particle lethargy and dose were calculated with MCNPX code. Neutron flux in a sample located at the end of collimator after normalized to measured value (Eid Mahmoud Eid Abdel Munem, 2007) at 1 MW power was 1.06E8 n/cm2/s. According to IAEA (2001) flux of 1.00E9 n/cm2/s requires three hours of treatment. Few modifications were needed to get higher flux.
Thermal neutron beam from thermal column was selected for a Boron Neutron Capture Therapy
(BNCT) system utilizing the Malaysian TRIGA MARK II reactor. Determination of shielding
materials for fast and epithermal neutron was conducted. The materials selected were polyethylene,
paraffin and water. For gamma-ray shielding, lead was used. The objective of this paper is to present
the simulation and verification of an optimal design of BNCT collimation at a beam. line viewing the
thermal column. A collimator was made from polyethylene pipe with 8 cm of diameter filled with
paraffin.