Purpose: Dose distributions are calculated by Monte Carlo (MC) simulations for two low-energy models 125 I brachytherapy source—IrSeed-125 and IsoAid Advantage (model IAI-125A)—loaded in the 14-mm standardized plaque of the COMS during treatment of choroid melanoma. Methods: In this study, at first, the radial dose function in water around 125 I brachytherapy sources was calculated based on the recommendations of the Task Group No. 43 American Association of Physicists in Medicine (TG-43U1 APPM) using by GATE code. Then, brachytherapy dose distribution of a new model of the human eye was investigated for a 14-mm COMS eye plaque loaded with these sources with GATE Monte Carlo simulation. Results: Results show that there are good agreements between simulation results of these sources and reporting measurements and simulations. Dosimetry results in the designed eye phantom for two types of iodine seeds show that the ratios of average dose of tumor to sclera, vitreous, and retina for IrSeed (IsoAid) source are 3.7 (3.7), 6.2 (6.1), and 6.3 (6.3), respectively, which represents the dose saving to healthy tissues. The maximum percentage differences between DVH curve of IsoAid and IrSeed seeds was about 8%. Conclusions Our simulation results show that although new model of the 125 I brachytherapy source having a slightly larger dimension than IAI-125A, it can be used for eye melanoma treatment because the COMS eye plaque loaded with IrSeed-125 could produce similar results to the IsoAid seeds, which is applicable for clinical plaque brachytherapy for uveal melanoma.

PURPOSE: The treatment efficiency of ⁹⁰Y and providing reliable estimates of activity are evaluated by SPECT imaging of bremsstrahlung radiation released during beta therapy. In this technique, the resulting spectrum from ⁹⁰Y is very complex and continuous, which creates difficulties on the imaging protocol. Moreover, collimator geometry has an impressive effect on the spatial resolution, system sensitivity, image contrast, and the signal-to-noise ratio (SNR), which should be optimized.METHODS: We evaluated the effect of energy window width, reconstruction algorithms, and different geometries of a medium-energy (ME) parallel-hole collimator on the image contrast and SNR of ⁹⁰Y SPECT images. The Siemens E.Cam gamma camera equipped with a ME collimator and a digital Jaszczak phantom were simulated by SIMIND Monte Carlo program to generate the ⁹⁰Y bremsstrahlung SPECT images.RESULTS: Our results showed that optimal image quality can be acquired by the reconstruction algorithm of OS-EM in the energy window width of 60 to 400 keV for ⁹⁰Y bremsstrahlung SPECT imaging. Furthermore, the optimal values of the hole diameter and hole length of a ME collimator were obtained 0.235 and 4.4 cm, respectively.CONCLUSIONS: The acquired optimal ME collimator and energy window along with using a suitable reconstruction algorithm lead to improved contrast and SNR of ⁹⁰Y bremsstrahlung images of hot spheres of the digital Jaszczak phantom. This can improve the accuracy and precision of the ⁹⁰Y activity distribution estimation after radioembolization in targeted radionuclide therapy.
Gamma Cameras ; Signal-To-Noise Ratio ; Tomography, Emission-Computed, Single-Photon

PURPOSE: The treatment efficiency of ⁹⁰Y and providing reliable estimates of activity are evaluated by SPECT imaging of bremsstrahlung radiation released during beta therapy. In this technique, the resulting spectrum from ⁹⁰Y is very complex and continuous, which creates difficulties on the imaging protocol. Moreover, collimator geometry has an impressive effect on the spatial resolution, system sensitivity, image contrast, and the signal-to-noise ratio (SNR), which should be optimized. METHODS: We evaluated the effect of energy window width, reconstruction algorithms, and different geometries of a medium-energy (ME) parallel-hole collimator on the image contrast and SNR of ⁹⁰Y SPECT images. The Siemens E.Cam gamma camera equipped with a ME collimator and a digital Jaszczak phantom were simulated by SIMIND Monte Carlo program to generate the ⁹⁰Y bremsstrahlung SPECT images. RESULTS: Our results showed that optimal image quality can be acquired by the reconstruction algorithm of OS-EM in the energy window width of 60 to 400 keV for ⁹⁰Y bremsstrahlung SPECT imaging. Furthermore, the optimal values of the hole diameter and hole length of a ME collimator were obtained 0.235 and 4.4 cm, respectively. CONCLUSIONS The acquired optimal ME collimator and energy window along with using a suitable reconstruction algorithm lead to improved contrast and SNR of ⁹⁰Y bremsstrahlung images of hot spheres of the digital Jaszczak phantom. This can improve the accuracy and precision of the ⁹⁰Y activity distribution estimation after radioembolization in targeted radionuclide therapy.