Purpose: This study aimed to evaluate the advantage of scatter limitation correction with misregistration between μ-map in the computed tomography attenuation correction and positron emission tomography in PET/CT study. Methods: We used torso phantom including simulated tumor and arms phantom. The CT scan was performed by changing the position of arms phantom after PET scan. Arms phantom movement was out-side direction, in-side direction, and top-side direction by 1–12 cm, respectively. The standardized uptake value (SUV) of simulated tumor and background (B.G.) were evaluated for three specific parameters. Two scatter corrections were performed with scatter correction (SC), and scatter limitation correction (SLC). Results: The SUVmax of simulated tumor was increased by 2.80% (SC), and 2.78% (SLC) on out-side arms movement. In the SUVmax, SC and SLC were decreased by 28.6%, 9.04% on in-side arms, respectively. SUVmax of the SC, and SLC were increased on top-side arms. The scatter fraction factor (SFF) of SC and SLC were 0.25, 0.25 on out-side 5 cm and were 0.732, 0.391 on in-side 5 cm and were 0.785, 0.434 on top-side 12 cm, respectively. Conclusion: SLC improved the overestimation of the SUVmax by SC. However, it is necessary to pay attention, in order not to be improved completely. The finding results indicated that SFF was setting 0.40–0.45 in our institute PET/CT system.
Boluses used in electron radiotherapy need to have radiation field visibility and water equivalence. In this report, we have examined field visibility and water equivalence of a new colorless transparent bolus. We examined field visibility, water equivalence, and dose profile. Field visibility was evaluated by comparison to conventional bolus. Water equivalence was investigated by a measured fluence scaling factor. The dose profile was measured by using radiochromic film with the bolus and an ionization chamber in water. We confirmed that the irradiation field could clearly be seen through the transparent colorless bolus. The bolus did not cast a field edge as compared with the conventional bolus. The fluence scaling factor was less than 0.8% as compared to water. We confirmed that the colorless transparent bolus was treated as a water equivalent material. The percentage depth dose (PDD) measured by using radiochromic film with the bolus matched the PDD measured with an ionization chamber in water. R50 was less than 1 mm as compared to PDD measured with an ionization chamber. It was confirmed that the colorless transparent bolus can use to set up patient without losing visibility on flat ground planes. The fluence scaling factor and dose profile measured by using the bolus matched the results measured in water. Therefore, the new colorless transparent bolus has feasibility to improve patient setup efficiency and can improve calculation accuracy by using the fluence scaling factor.
Excess acquisition counts were often obtained by the current image acquisition of 30 minutes after 123I-ioflupane administration in a dopamine transporter study. The purpose of this study was to calculate the minimum acquisition time while retaining sufficient image quality, which could be adjusted for individual characteristics. Fifty patients who underwent dopamine transporter imaging were included in this retrospective study. The brain count density, determined by a striatum phantom, was compared to the participant’s characteristics. The individual characteristics were divided into five categories of gender, age, height, weight, and body mass index. The values of 40 counts / voxel (brain count density) were set as the image quality criteria by the striatum phantom study. Weight was the characteristic that most correlated with brain count density in the 50 patients (correlation coefficient: −0.728). The acquisition time for the 50 patients was calculated as 23.4±2.6 minutes using the following formula: 0.332×W+5.42 minutes (W kg (individual weight)). A shorter acquisition time with sufficient image quality can be achieved by adjusting for individual patient weight.