Study of the impact of tissue density heterogeneities on 3-dimensional abdominal dosimetry: comparison between dose kernel convolution and direct monte carlo methods.

Dose kernel convolution (DK) methods have been proposed to speed up absorbed dose calculations in molecular radionuclide therapy. Our aim was to evaluate the impact of tissue density heterogeneities (TDH) on dosimetry when using a DK method and to propose a simple density-correction method. METHODS: This study has been conducted on 3 clinical cases: case 1, non-Hodgkin lymphoma treated with (131)I-tositumomab; case 2, a neuroendocrine tumor treatment simulated with (177)Lu-peptides; and case 3, hepatocellular carcinoma treated with (90)Y-microspheres. Absorbed dose calculations were performed using a direct Monte Carlo approach accounting for TDH (3D-RD), and a DK approach (VoxelDose, or VD). For each individual voxel, the VD absorbed dose, D(VD), calculated assuming uniform density, was corrected for density, giving D(VDd). The average 3D-RD absorbed dose values, D(3DRD), were compared with D(VD) and D(VDd), using the relative difference Δ(VD/3DRD). At the voxel level, density-binned Δ(VD/3DRD) and Δ(VDd/3DRD) were plotted against ρ and fitted with a linear regression. RESULTS: The D(VD) calculations showed a good agreement with D(3DRD). Δ(VD/3DRD) was less than 3.5%, except for the tumor of case 1 (5.9%) and the renal cortex of case 2 (5.6%). At the voxel level, the Δ(VD/3DRD) range was 0%-14% for cases 1 and 2, and -3% to 7% for case 3. All 3 cases showed a linear relationship between voxel bin-averaged Δ(VD/3DRD) and density, ρ: case 1 (Δ = -0.56ρ + 0.62, R(2) = 0.93), case 2 (Δ = -0.91ρ + 0.96, R(2) = 0.99), and case 3 (Δ = -0.69ρ + 0.72, R(2) = 0.91). The density correction improved the agreement of the DK method with the Monte Carlo approach (Δ(VDd/3DRD) < 1.1%), but with a lesser extent for the tumor of case 1 (3.1%). At the voxel level, the Δ(VDd/3DRD) range decreased for the 3 clinical cases (case 1, -1% to 4%; case 2, -0.5% to 1.5%, and -1.5% to 2%). No more linear regression existed for cases 2 and 3, contrary to case 1 (Δ = 0.41ρ - 0.38, R(2) = 0.88) although the slope in case 1 was less pronounced. CONCLUSION: This study shows a small influence of TDH in the abdominal region for 3 representative clinical cases. A simple density-correction method was proposed and improved the comparison in the absorbed dose calculations when using our voxel S value implementation

Matrices A such that R A = A^{s + 1} R when R^k = I

This paper examines matrices A∈C^(n×n) such that R A = A^(s+1) R where R^k = I, the identity matrix, and where s and k are nonnegative integers with k⩾2. Spectral theory is used to characterize these matrices. The cases s = 0 and s⩾1 are considered separately since they are analyzed by different techniques

99mTc-IgG-Lung Scintigraphy in the Assessment of Pulmonary Involvement in Interstitial Lung Disease and Its Comparison With Pulmonary Function Tests and High-Resolution Computed Tomography: A Preliminary Study

Background: The discrimination of inactive inflammatory processes from the active form of the disease is of great importance in the management of interstitial lung disease (ILD). Objectives: The aim of this study was to determine the efficacy of 99mTc-IgG scan for the detection of severity of disease compared to high-resolution computed tomography (HRCT) and pulmonary function test (PFT). Patients and Methods: Eight known cases of ILD including four cases of Mustard gas (MG) intoxication and four patients with ILD of unknown cause were included in this study. A population of six patients without lung disease was considered as the control group. The patients underwent PFT and high-resolution computed tomography scan, followed by 99mTc-IgG scan. They were followed up for one year. 99mTc-IgG scan assessment of IgG uptake was accomplished both qualitatively (subjectively) and semiquantitatively. Results: All eight ILD patients demonstrated a strong increase in 99mTc-IgG uptake in the lungs, compared to the control patients. The 99mTc-IgG scan scores were higher in the patient group (0.64[95% confidence interval (CI)=0.61-0.69])) than the control group (0.35 (0.35[95% CI=0.28-0.40]), (P 0.05). There were no significant correlations between 99mTc-IgG score and HRCT patterns including ground glass opacity, reticular fibrosis and honeycombing (P value > 0.05). Conclusion: The present results confirmed that 99mTc-IgG scan could be applied to detect the severity of pulmonary involvement, which was well correlated with HRCT findings. This data also showed that the 99mTc-IgG scan might be used as a complement to HRCT in the functional evaluation of the clinical status in ILD; however, further studies are recommended