RESUMEN
PURPOSE: The purpose of this study is to quantify the change in monthly VMAT quality assurance (QA) and determine the tests to maintain consistent delivery with a baseline. METHODS: VMAT monthly QA has been performed for over 14 months on two Elekta Synergy LINACs. A baseline was established at acceptance and the monthly QA results were compared to those initial values. Films were used to test the dependence on varying dose rate, gantry speed, rotational direction, and MLC speed. These parameters were tested independently and then together in a test called the synchronicity test. Ion chamber readings test a DMLC field with a varying dose rate and MLC speed. Introducing intentional errors into the tested fields allowed the detectable limits of the QA to be determined. RESULTS: The monthly QA has consistently matched the baseline within a 3% dose limit on film. Analyzing the synchronicity film with a gamma test using a 5%/0.5mm tolerance showed a monthly pass rate of over 99%. The DMLC test has been identical for the entire course of VMAT QA. Furthermore, intentional changes in the MLC speed were noticed on the synchronicity test in the form of a smaller gamma pass rate as the MLC error was increased. CONCLUSIONS: There is a monthly agreement with all films testing individual parameters, ion chamber DMLC readings, as well as agreement with the synchronicity test. This collection of data has lead to the conclusion that only the synchronicity test and DMLC readings need to be performed on a monthly basis. If those tests fail, then individual parameters need to be tested to determine the singular cause of the error. Having a single test used as a red flag increases the efficiency of the monthly QA and is being implemented with an EPID to eliminate the use of film.
RESUMEN
PURPOSE: To quantify the change, if any, in flexmap correction factors and image quality with the XVI system over a course of several years and from these results, assess their clinical impact. METHODS: Flexmap, a calibration procedure which corrects for imperfect gantry rotation for cone-beam CT reconstruction, and image quality tests were performed on three Elekta Synergy linacs equipped with XVI. Data was collected per month over three years. U and V values, corresponding to lateral and longitudinal shifts respectively, were acquired through the XVI software. Image quality parameters were obtained through CT imaging of the Catphan 500®. For each reconstruction, pixel values for low density polyethylene (LDPE) and polystyrene materials were recorded. RESULTS: For all three linacs, analysis of the flexmap showed a significant change in the U factor for both month-to-month comparisons and comparisons between machines. The V correction factor exhibited a small variation month to month, and showed a slight, gradual increase over time (0.2 +/-0.08 mm). Image quality analysis showed a near consistent decrease (5-10%) in LDPE and polystyrene. Despite this decrease in pixel values, the ratio of the two pixel values remained constant, thus a similar decreasing trend in contrast was not observed. CONCLUSIONS: Analysis of monthly flexmap calibration showed the general monthly change in correction shifts and their general trend over several years. For image quality, our research exhibited roughly 0.5% per month decrease in pixel values of the Catphan®. Our results imply that CBCT images obtained from XVI are not appropriate for treatment planning and despite the decrease in panel response over time, image quality with respect to contrast will remain within acceptable clinical standards. Future studies may be carried out to assess any correlation between image quality and XVI source strength.
RESUMEN
The influence of different risk factors for viral hepatitis A, B and C, particularly if sexual contact with the indigenous population was related to an increased risk of having hepatitis B virus (HBV) markers, was assessed by multivariate analysis in a logistic regression model in a prospectively enrolled series of 563 adult Swedish expatriates. The most frequently reported recognised risk factors for the acquisition of viral hepatitis (as reported in a self-administered questionnaire) were having received an inoculation during medical or dental treatment, reported by 45% of all subjects, and having had sexual contact with the indigenous population, reported by 35%. Whilst the prevalences of hepatitis A virus (HAV) and hepatitis C virus (HCV) markers in these expatriates were of the same magnitude as previously reported in the general Swedish population, 8% and 0.3%, respectively, the prevalence of markers for a past or present HBV infection was about twice as high (5%). The presence of HBV markers was associated with being a health care professional or having received inoculations during medical or dental treatment in Africa. No significant association was found between having HBV markers and having had sexual contact with the indigenous population.
Asunto(s)
Hepatitis A/epidemiología , Hepatitis B/epidemiología , Hepatitis C/epidemiología , Viaje , Adolescente , Adulto , Biomarcadores , Transfusión Sanguínea , Coito , Hepatitis A/etiología , Hepatitis B/etiología , Hepatitis C/etiología , Humanos , Inyecciones , Compartición de Agujas , Ocupaciones , Estudios Prospectivos , Factores de Riesgo , Asunción de Riesgos , Parejas Sexuales , Encuestas y Cuestionarios , Suecia/epidemiología , Suecia/etnologíaRESUMEN
The in vivo response of Plasmodium falciparum to chloroquine and to pyrimethamine/sulfadoxine was studied for seven days in schoolchildren from two villages 30 to 40 km north of Dar es Salaam. Standard therapeutic regimen of chloroquine (25 mg base kg-1) failed to clear parasitaemia in 17 of 62 (27%) treated subjects. In contrast, standard treatment with pyrimethamine/sulfadoxine cleared the parasitaemia in all 44 treated subjects within five days. Hence, in the studied area, the therapeutic effect of sulfadoxine/pyrimethamine was superior to that of chloroquine.