جستجوی مقالات مرتبط با کلیدواژه "correction factor" در نشریات گروه "پزشکی"

Neutron dosimetry is a challenging subject in radiation protection. Responses of neutron dosimeters mostly depend on the neutron energy spectrum. Dosimeter response corresponding to a dose-equivalent in the calibration field is different from responses in other neutron fields. Consequently, the dose estimated by neutron dosimeters may be associated with great uncertainty. Therefore, the present study aimed to modify the response in different neutron fields in order to reduce this uncertainty.

Thermo-luminescent dosimeters (TLDs) are widely used to determine neutron dose-equivalent. In the present study, a set of TLD-600 and TLD-700 dosimeters included in a TLD card was utilized to determine the response to “fast” neutrons of 241Am-Be,252Cf, and 239Pu-Be standard fields in four dose-equivalents of 5, 10, 15, and 20 mSv. Meanwhile, 241Am-Be was regarded as the calibration field.

As evidenced by the obtained results, for equal dose-equivalents, the original responses in 252Cf and 239Pu-Be fields are smaller, compared to those in the 241Am-Be filed. The maximum discrepancies were obtained at 26.8% and 42.5% occurring at 20 and 5 mSv, respectively. After the application of a correction factor equal to the average of relative responses (i.e., in 241Am-Be to two other fields) corresponding to all dose-equivalents considered, these differences reduced to 12.4% and 21.7%.

It can be concluded that the correction method used in the present study could enhance the accuracy of dose estimated by TLDs in fast neutron fields.

Nowadays in most researches, thermoluminescent dosimeters are used as a practical implement for dosimetry systems. In this study, we calibrated thermoluminescent dosimeters by Gamma knife 4C and Theratron 780-C units as gamma emitters in low dose conditions and moreover compared the response of both calibration curves to consider possibility of using every device’s calibration curves instead of the other instrument.
Calibration curves of Theratron 780-C machine and Gamma knife 4C unit were measured and plotted in low dose conditions. In order to conduct individual calibration, TLDs were exposed with dose of 100 cGy and through group calibration, dosimeters were divided into 7 groups and were exposed with doses of 0-12 cGy in both machines. To evaluate TLD response by changing field size, TLDs were irradiated with different field sizes in Theratron 780-C and with different collimator sizes in Gamma knife 4C. The best fitting curves were obtained with Excell and Matlab software.
By complying with the best fitting curves for the TLD-100 and conforming to Fisher's test, calculated p-value was 0.92, which was greater than 0.05, therefore the difference is not significant between two calibration curves.
Regardless of differences in calibration conditions between Theratron 780-C machine and Gamma Knife 4C unit, the results showed that every one of these devices can be replaced and used to estimate the unknown dose both in stereotactic radiosurgery and radiotherapy.

The diagnostic accuracy of single photon emission computed tomography (SPECT) is profoundly influenced by attenuation phenomenon. Soft tissue attenuation degrades cardiac SPECT image quality, thereby decreasing the possibility of the detection of the lesions. A variety of correction techniques based on different assumptions have been used to reduce the impact of attenuation. Several types of systems with different transmission hardware modifications and external sources have been developed for clinical implementation. Each system has unique advantages and limitations. In this study, firstly, we introduce the attenuation phenomenon, the problems arising from it and the attenuation correction methods with description of the assumptions related to each of them. The main purpose of this study is to review the developments in the field involving various configurations used for attenuation correction of SPECT images, as tested using either phantom or clinical data, and to delineate an optimal attenuation correction technique by considering the advantages and limitations with each of the configurations.