Neutron dose equivalent measured at the maze door with various openings for the jaws and MLC.

PURPOSE: This study was undertaken to explore the effects of the jaws and the MLC openings on the neutron dose equivalent (DE) at the maze door and neutron flux at the patient plane. METHODS: The neutron dose equivalent was measured at the maze entrance door of a 15 MV therapy linear accelerator room. All measurements were performed using various field sizes up to 40 cm × 40 cm. Activation detectors constructed from natural Indium (In) were exposed at Cd envelope to neutrons in order to estimate relative changes of epithermal neutron fluences in the patient plane. RESULTS: Our study showed that the dose equivalent at the maze door is at the highest when the jaw are closed and that maximal jaws opening reduces the DE by more than 20%. The neutron dose equivalent at the maze door measured for radiation fields defined by jaws do not differ significantly from the DE measured when MLC determines the same size radiation field. The epithermal capture reaction rate measured using different jaw openings differs by approximately 10%. When an MLC leaf is inserted into a fixed geometry for one opening of the jaws, an increase of the epithermal neutron capture reaction rate in Indium activation detectors was observed. CONCLUSIONS: There is no significant difference in the neutron DE when MLC defines radiation field instead of jaws. This leads to the conclusion that the overall number of neutrons remains similar and it does not depend on how primary photon beam was stopped-by the jaws or the MLC. An increase of the fast neutron capture reaction rate when MLC leaves are inserted probably originates from the neutron scattering.

[Autoimmune hepatitis and/or hepatitis C]. / Autoimunski hepatitis i/ili hepatitis "C".

UNLABELLED: Hepatitis C virus (HCV) was identified in 1989 as a primary aetiologic agent of parenterally transmitted non-A non-B hepatitis and a major cause of acute and chronic hepatitis worldwide [1, 2]. Extrahepatic manifestations that are associated with chronic HCV infection include: type II cryoglobulinaemia, membranoproliferative glomerulonephritis, porphyria cutanea tarda, Sjogren syndrome, autoimmune thyroiditis, lichen planus, etc. [3, 4]. Likewise, there is a very interesting link between HCV and autoimmune hepatitis type I [5-7]. The second generation of immunoassays confirmed positive anti HCV in a relatively low percent of patients (0-5%) with autoimmune hepatitis type I [5-7]. This fact suggests that HCV infection is not an important factor in the pathogenesis of autoimmune hepatitis, but it is not excluded. The examination of autoimmune markers is highly significant for the proper decision of the therapy: interferon therapy leads to exacerbation of autoimmune hepatitis, while corticosteroids enhance virus replication in patients with HCV infection. There is a percentage of patients suffering from both diseases, and in this case the therapeutic strategy is the treatment of predominant disease. The aim of the study was to establish the proper diagnose and make an adequate therapeutic decision in HCV infection combined with positive autoantibody findings. PATIENTS AND METHODS: In our study forty nine patients with HCV infection of autoimmune markers are described. Diagnosis of HCV infection was confirmed by clinical, biochemical, serological and histological examinations. ANA, AMA, and ASMA as non-specific autoimmune markers have been studied. Significant titre of ANA is 1:80, AMA 1:40 and ASMA 1:20 or higher. The patients included in the study were HBsAg negative, anti-HCV positive (at least six months) and had no sign of any other chronic disease, such as Morbus Wilson, alpha-1-antitrypsin deficiency or haemochromatosis. RESULTS: The relevant data on patients are shown in Table 1. It is evident that 45% of patients had no known risk factors. The results of autoantibody are shown in Table 2. Eleven patients (22%) had autoantibodies, of whom one had 1:40 titre of ANA, while three had 1:80 titre of ASMA. Positive titre of AMA 1:40 was found in two patients. The distribution of relative autoantibody concentrations showed insignificant titres. The interferon therapy was used in five HCV RNA positive cases without progression. DISCUSSION: Pathologic immune responses are sometimes the primary cause of autoimmune disorder, and sometimes the second one. The best studied factors that produce autoimmune disorder, are viruses. Probably the best evidence of virus aetiology of autoimmune hepatitis is the presence of anti-HCV antibody in some patients with autoimmune hepatitis type 1. Our clinical trial revealed the presence of autoantibodies in 22% of patients who suffered from HCV infection. These results are very similar to those of other authors [3, 5, 6, 16]. From the clinical point of view all patients can be divided into three groups: 1) The first group consists of patients with false positive results of anti-HCV and "true" autoimmune hepatitis type 1. Corticosteroid treatment is recommended. 2) The second group consists of patients with HCV infection and low percent of autoantibodies titres. These patients should be treated with alpha-interferon. 3) The third group consists of patients suffering from both diseases: chronic hepatitis C and autoimmune hepatitis. In this case, the initial treatment should start with corticosteroids (as low risk therapy) but if the progression is still on, corticosteroids should be substituted by interferon therapy. Our patients belonged to the second group, because of nonspecific titres of relative autoantibody concentrations. Our conclusion was that none of these patients had autoimmune hepatitis but certain autoimmune phenomena. The interferon therapy was used in five HCV RNA positive cases without

Pre-school visually impaired children: visual stimulation and micro-computers.

A justification is offered for using micro-computers and specially-designed programs with severely visually impaired pre-school children. It is argued that this technology optimizes the visual environment for the child and provides immediate feedback about the correctness of his responses to the stimuli displayed on the screen. Some of the problems encountered in such use are described, with examples taken from sessions in which teachers are working with children as young as 2 years of age, using teaching/learning sequences designed to promote and exercise visual perception skills. Among the issues addressed are the nature of the language interactions between child and adult, the effects of altering the complexity of the tasks, and the possible value of formal task analysis as a means of enabling the teacher to pinpoint critical stages in the learning process.