SIZE-SPECIFIC DOSE ESTIMATES FOR PEDIATRIC NON-CONTRAST HEAD CT SCANS: A RETROSPECTIVE PATIENT STUDY IN TUNJA, COLOMBIA.

This investigation is aimed to study the feasibility of size-specific dose estimate (SSDE) to patient dosimetry in pediatric head CT scans and to establish typical values in a hospital in Tunja, Colombia. The volumetric computed tomography index (CTDIvol) and the dose-length product of 468 pediatric patients from newborn to 15-year-olds, who underwent non-contrast head CT scans, were collected retrospectively. For 186 cases only, SSDE was estimated using patient attenuated-based size metrics and CTDIvol,16-to-SSDE conversion factors reported in AAPM report 293. Results showed that SSDE is an accurate metric that can be used to establish typical dose values from pediatric head CT scans. Median SSDE values of 33.5, 31.6, 36.2 and 57.9 mGy were established as typical dose values for the 0-<3 months, 3 months-<1 y, 1-<6 y and ≥6 y, respectively, to further assist the optimization process at the hospital. Further studies with more robust data of patients and hospitals should be conducted to establish local and national dose reference levels from pediatric CT scans in Colombia.

Shielding for transporting an 241Am-Be source for industrial applications.

Paraffin, water and water-extended polyester (WEP) were used as main moderator to design a mobile shielding for a 666 GBq 241Am-Be source used in oil industry. The shielding performance was estimated using Monte Carlo methods where the γ-rays induced by the neutron interaction with the shielding materials were also included. The spectra of neutrons and γ-rays around the shielding were estimated, as well as the total neutron and g-ray total fluences per history. The neutron source strength was used to calculate ambient dose equivalent rates, aiming to satisfy the international recommendation (2 mSv/h at the shielding surface). Moderators modify the neutron spectrum of the source reducing the amount of fast neutrons (0.5-11 MeV) and producing epithermal and thermal neutrons. During neutron transport in the moderator neutron capture and inelastic scattering produce gamma-rays. Paraffin has the best shielding performance however it is not suitable because can be affected by extreme temperatures. WEP and water have similar shielding performance, however water do not satisfy the international recommendations because at one site the neutron and γ-ray doses rates are larger than 2 mSv/h. WEP is the best option because fulfill the international recommendations, it is stable and temperatures where paraffin fails. The WEP-based shielding weights 66 kg.