Study of the photoneutron generation caused by a LinAc Beryllium window with a 6 MeV treatment beam.

In most conventional radiation therapy treatments, special attention is payed for neutron contamination when working with energy beams above 8 MeV and generally it is only considered for shielding requirements, not for dose study in patients or employees. The present work is focused on studying the unwanted generated photoneutrons in a Medical Linear Accelerator (LinAc) Varian TrueBeam using a 6 MeV radiation treatment beam. To that, Monte Carlo (MC) simulation code MCNP6.1.1 was used. This version of the code allows the use of unstructured mesh geometries as a novelty, offering more reliable results and higher speed computation. The particularity of the studied LinAc is the presence of a beryllium filter at the treatment head. Since Beryllium causes photonuclear reactions (γ, n) at energies much lower than other LinAc composing materials, this work aims to analyze if this type of units, when using low energy treatment beams (6 MeV), produce neutron pollution and to ensure that this unwanted radiation can be considered negligible.

Nicardipine as antihypertensive therapy in liver transplant recipients: results of long-term use.

Arterial hypertension is frequent in liver transplant recipients on cyclosporine A (CsA). Nicardipine is a calcium channel blocker (CCB) that has been shown to be efficient in controlling postoperative hypertension. However, its use has been limited in organ recipients because of its reported interaction with CsA metabolism. In this report, we studied the results of the long-term use of nicardipine after liver transplantation. Forty-nine consecutive liver transplant recipients with a follow-up longer than 2 years were studied. Immunosuppressive regimen was based on CsA and prednisone. Patients with immediate postoperative hypertension received intravenous nicardipine, secondarily switched to oral nicardipine (group 1, n = 27). Patients with delayed hypertension (i.e., >2 weeks posttransplant) received other antihypertensive drugs which did not interact with CsA metabolism. These patients and those without hypertension formed group 2 (n = 22). The two groups were similar for age, sex, body weight, and transplantation indications. Interaction of nicardipine with CsA metabolism was confirmed. Whereas cyclosporine blood levels were similar in both groups at any time during the study, the mean cyclosporine daily dose required to achieve such levels was 30% lower in group 1 compared with group 2 (P < .01). This resulted in a significant cost-containment. The use of nicardipine was not associated with an increased incidence of graft rejection or CsA toxicity episodes. The results in liver transplant recipients showed that nicardipine interacts with CsA metabolism, leading to a 30% reduction in CsA dose and does not increase the risk of CsA toxicity or graft rejection. Nicardipine can be used safely for the treatment of arterial hypertension after liver transplantation with a potential cost-containment.