EchoSeed Model 6733 Iodine-125 brachytherapy source: improved dosimetric characterization using the MCNP5 Monte Carlo code

This study primarily aimed to obtain the dosimetric characteristics of the Model 6733 (125)I seed (EchoSeed) with improved precision and accuracy using a more up-to-date Monte-Carlo code and data (MCNP5) compared to previously published results, including an uncertainty analysis. Its secondary aim was to compare the results obtained using the MCNP5, MCNP4c2, and PTRAN codes for simulation of this low-energy photon-emitting source. The EchoSeed geometry and chemical compositions together with a published (125)I spectrum were used to perform dosimetric characterization of this source as per the updated AAPM TG-43 protocol. These simulations were performed in liquid water material in order to obtain the clinically applicable dosimetric parameters for this source model. Dose rate constants in liquid water, derived from MCNP4c2 and MCNP5 simulations, were found to be 0.993 cGyh(-1)?U(-1) (±1.73%) and 0.965 cGyh(-1)?U(-1) (±1.68%), respectively. Overall, the MCNP5 derived radial dose and 2D anisotropy functions results were generally closer to the measured data (within ±4%) than MCNP4c and the published data for PTRAN code (Version 7.43), while the opposite was seen for dose rate constant. The generally improved MCNP5 Monte Carlo simulation may be attributed to a more recent and accurate cross-section library. However, some of the data points in the results obtained from the above-mentioned Monte Carlo codes showed no statistically significant differences. Derived dosimetric characteristics in liquid water are provided for clinical applications of this source model.     

Thrombotic microangiopathy syndrome as an AIDS-defining illness: the experience of J. Stroger Hospital of Cook County

Thrombotic thrombocytopenic purpura and hemolytic uremic syndrome are severe life-threatening disseminated thrombotic microangiopathies (TMA). Although many cases are idiopathic, TMA can occur in association with pregnancy, malignancy, autoimmune diseases, and HIV infection. We retrospectively analyzed the cases of 17 patients with TMA coexistent with HIV infection admitted to our institution. Median T-cell count at presentation was 28 cells/mm3 Patients presented with severe thrombocytopenia (median platelet count 19 x 10(9)/L) and high lactate dehydrogenase levels (median 1,057 U/L). The majority of patients (82%) presented with renal dysfunction. Forty-one percent of patients had fever and 29% had neurological signs at presentation, which were associated with inferior outcome. Despite plasma exchange, inpatient mortality for the first TMA episode was 47%. Some patients relapsed following an initial TMA episode. However, there were responders with remissions lasting 5 years. We conclude that TMA, coexistent with an HIV-associated low CD4 count, is a treatable condition. Considering TMA as an AIDS-defining illness may help clinicians recognize this syndrome earlier, leading to prompter treatment and improved survival rates.     

Stem cell transplantation with reduced-intensity conditioning for hemophagocytic lymphohistiocytosis

Allogeneic stem cell transplantation (SCT) is curative for hemophagocytic lymphohistiocytosis (HLH). However, patients frequently have significant morbidity before transplantation and there is high transplant-related mortality (TRM). Because first-degree HLH is caused by immune dysregulation, a reduced-intensity conditioned (RIC) regimen might be sufficient for cure while decreasing the TRM. Twelve patients with HLH underwent RIC SCT from a matched family/unrelated or haploidentical donor. Eleven were conditioned with fludarabine/melphalan with additional busulphan for haploidentical grafts. One received fludarabine and 2-Gy total body irradiation (TBI). All patients showed engraftment at a median of 14 days. Nine of 12 (75%) are alive and in complete remission (CR) a median of 30 months (range, 9-73 months) after SCT. Two patients died from pneumonitis and one from hepatic rupture. Four patients developed acute graft-versus-host disease (GVHD) and 3 have chronic GVHD. Three of 9 survivors have mixed chimerism but remain free of disease. In summary, RIC compares favorably to conventional SCT with long-term disease control in surviving patients despite a significant incidence of mixed chimerism.