The Evaluation of Scattering Effects for Various Source Locations within a Phantom in Gamma Camera / 의학물리

ABSTRACT

(131)I is a radiological isotope being used widely for treatment of cancer as emitting gamma-ray and it is also applied to estimate the function of thyroid for its accumulation in thyroid. However, (131)I is more difficult to quantitate comapred to (99m)Tc, because (131)I has multiple energy gamma-ray emissions compared to (99m)Tc which is a mono energetic gamma-ray source. Especially, scattered ray and septal penetration resulted by high energy gamma ray have a bad influence upon nuclear medicine image. The purpose of this study was to estimate scatter components depending on the different source locations within a phantom using Monte Carlo simulation (GATE). The simulation results were validated by comparing with the results of real experiments. Dual-head gamma camera (ECAM, Chicago, Illinois Siemens) with high energy, general-purpose, and parallel hole collimators (hole radius 0.17 cm, septal thickness 0.2 cm, length 5.08 cm) was used in this experiment. The NaI crystal is 44.5x59.1 cm in height and width and 0.95 cm in thickness. The diameter and height of PMMA phantom were 16 cm and 15 cm, respectively. The images were acquired at 5 different locations of (131)I point source within the phantom and the images of (99m)Tc were also acquired for comparison purpose with low energy source. The simulation results indicated that the scattering was influenced by the location of source within a phantom. The scattering effects showed the same tendency in both simulation and actual experiment, and the results showed that the simulation was very adequate for further studies. The results supported that the simulation techniques may be used to generalize the scattering effects as a function of a point source location within a phantom.