Search

Purpose Size-specific dose estimates (SSDEs) are the latest focus of interest among medical physicists studying radiation dose to the patient in computed tomography (CT). This study aims to make conversions from CTDIvol to SSDE and investigate the relationship between mean SSDE (SSDE) and central SSDE (SSDEcenter) values for pediatric patients of different age groups undergoing chest, abdomen, and pelvis scans. Methods In this retrospective study, we examined 105 consecutive pediatric CT exams of chest, abdomen, and pelvis (CAP) classified in 3 separate groups according to age: 0-5 years, 6-10 years, and 11-16 years. A MATLAB program was developed to determine SSDE values for each patient along 6 subregions: chest, abdomen, pelvis, chest and abdomen, abdomen and pelvis, and CAP. SSDE values derived over the slice at the center of each scan range (SSDEcenter) were also recorded. SSDE and corresponding SSDEcenter results were compared for each age group. Results Root mean square differences (RMSD) between SSDE and SSDEcenter values ranged between 0.13 mGy and 2.1 mGy through all groups and subregions, corresponding to 1.2% and 11%, respectively. Conclusion In pediatric CT exams involving CAP region, CTDIvol and the water equivalent diameter at the middle of the scan range can be used to provide a reasonable estimate of mean SSDE with an RMSD of 11% at most.

The behavior of beta particles under the magnetic field was investigated both theoretically and experimentally based on the assumption of reducing the damage to the normal tissues created by using magnetic field in radionuclide therapy.A water-filled spherical medium and a beta particle source was formed by using Geant4 simulation software for the theoretical study. After applying a homogenous magnetic field, the volume of points at which the particles interact with the medium was calculated by determining particle range. The range of beta particles was examined using yttrium-90 source and Gafchromic films for the experimental study. The setup was kept in normal room conditions and in the magnetic resonance imaging device. Then the irradiated films were analyzed by creating isodose curves.With the increase of the magnetic field, the number of hits at the center was increased, but the number of hits at the outer boundaries decreased inversely proportional to the strength of the magnetic field. The change perpendicular to the magnetic field was greater as compared to the change parallel to the magnetic field. The volume of hits of beta particles got smaller with the increase of the magnetic field.When magnetic field is increased, the decrease in the number of interactions at the outer boundaries became more pronounced in the perpendicular direction to the magnetic field. The effect of magnetic field was more apparent for higher energy beta particles than lower energy particles.Amaç: Beta yayan radyoizotoplarla yapılan kanser tedavilerinde manyetik alan kullanılarak normal dokularda oluşan zararın azaltılmasının mümkün olabileceği varsayımı ile beta parçacıklarının manyetik alandaki davranışları teorik ve deneysel olarak araştırıldı. Yöntem: Teorik çalışmada, Geant4 programında içi su dolu küresel bir ortam oluşturuldu ve merkezine beta parçacığı kaynağı yerleştirildi. Homojen bir manyetik alan uygulanarak parçacıkların ortamla etkileştikleri noktaların hacmi, parçacıklarının menzilleri belirlenerek hesaplandı. Deneysel çalışmada, beta parçacıklarının menzili itriyum-90 kaynağı ve Gafkromik film kullanılarak incelendi. Düzenek normal oda koşullarında ve manyetik rezonans görüntüleme cihazında bekletildi. Işınlanan filmler izodoz eğrileri oluşturularak analiz edildi. Bulgular: Manyetik alan artmasıyla beraber merkezde etkileşim sayısında artma olduğu, merkezin dışında ise etkileşim sayısının manyetik alanla ters orantılı olarak azaldığı görüldü. Manyetik alana dik yöndeki değişim manyetik alana paralel yöndekine göre daha fazla idi. Manyetik alanın artmasıyla beta parçacıklarının etkileştiği hacim küçülmekte idi. Sonuç: Manyetik alan arttıkça, manyetik alana dik yönlerde merkezin dışındaki alanlarda etkileşim sayısındaki azalım daha belirgin olmaktadır. Manyetik alan etkisinin düşük enerjililere oranla yüksek enerjili beta parçacıklarında daha belirgin olduğu görülmüştür.

IntroductionVolumecomputed tomography dose index(CTDIvol) does not contain any dose information regarding the patient size. Size specific dose estimates (SSDE) give more reliable results accounting for the patient size as well. This parameter uses CTDIvol and size dependent conversion factors (fDw) which are calculated by means of water equivalent diameter (Dw) of the patient cross section in every slice of image.PurposeTo develop software to automatically calculate SSDE and to assess the impact of variations in Dw along the z axis on SSDE for CT examinations of the torso in pediatric patients.Materials and methods55 consecutive CT exams of the combined chest, abdomen and pelvis (CAP) have been examined. SSDE has been calculated for 6 hypothetical scan ranges: chest alone, abdomen alone, pelvis alone, chest and abdomen, abdomen and pelvis, and CAP. Two methods were used in mean SSDE approach: (1) mean SSDE over each scan range; (2) SSDE value at the middle of the scan range.ResultsFor scan ranges 1 to 6, the average of the difference in maximal and minimal Dw accross patients was 3.7, 3.8, 2.6, 4.1, 4.4 and 4.5 cm. The mean SSDE values calculated using methods (1) and (2) were highly compatible, with root mean square differences of 0.4, 0.5, 0.3, 1.0, 1.5 and 0.7mGy or 3%, 4%, 2%, 7%, 10%, 5%.ConclusionUsing the mean CTDIvol and the water equivalent diameter at the middle of the scan range provides a reasonable estimation of patient dose in pediatric exams.