Air kerma standard for calibration of well-type chambers in Brazil using 192Ir HDR sources and its traceability.

In Brazil there are over 100 high dose rate (HDR) brachytherapy facilities using well-type chambers for the determination of the air kerma rate of 192Ir sources. This paper presents the methodology developed and extensively tested by the Laboratorio de Ciencias Radiologicas (LCR) and presently in use to calibrate those types of chambers. The system was initially used to calibrate six well-type chambers of brachytherapy services, and the maximum deviation of only 1.0% was observed between the calibration coefficients obtained and the ones in the calibration certificate provided by the UWADCL. In addition to its traceability to the Brazilian National Standards, the whole system was taken to the University of Wisconsin Accredited Dosimetry Calibration Laboratory (UWADCL) for a direct comparison and the same formalism to calculate the air kerma was used. The comparison results between the two laboratories show an agreement of 0.9% for the calibration coefficients. Three Brazilian well-type chambers were calibrated at the UWADCL, and by LCR, in Brazil, using the developed system and a clinical HDR machine. The results of the calibration of three well chambers have shown an agreement better than 1.0%. Uncertainty analyses involving the measurements made both at the UWADCL and LCR laboratories are discussed.

A feasibility study of Fricke dosimetry as an absorbed dose to water standard for 192Ir HDR sources.

High dose rate brachytherapy (HDR) using 192Ir sources is well accepted as an important treatment option and thus requires an accurate dosimetry standard. However, a dosimetry standard for the direct measurement of the absolute dose to water for this particular source type is currently not available. An improved standard for the absorbed dose to water based on Fricke dosimetry of HDR 192Ir brachytherapy sources is presented in this study. The main goal of this paper is to demonstrate the potential usefulness of the Fricke dosimetry technique for the standardization of the quantity absorbed dose to water for 192Ir sources. A molded, double-walled, spherical vessel for water containing the Fricke solution was constructed based on the Fricke system. The authors measured the absorbed dose to water and compared it with the doses calculated using the AAPM TG-43 report. The overall combined uncertainty associated with the measurements using Fricke dosimetry was 1.4% for k = 1, which is better than the uncertainties reported in previous studies. These results are promising; hence, the use of Fricke dosimetry to measure the absorbed dose to water as a standard for HDR 192Ir may be possible in the future.

Chemotherapy and radiation regimens to breast cancer treatment induce changes in mRNA levels of renin-angiotensin system related genes in cardiac tissue.

BACKGROUND AND AIM: Cardiovascular complications are one limitation of breast cancer treatment. The aim of the current study was to investigate whether the renin-angiotensin related genes could be altered by chemotherapy and radiotherapy, using a rat model. METHODS: Female rats were divided into three groups: control, chemotherapy + irradiation (TC+IR) and irradiation (IR). Molecular analyses of the left ventricle were performed five months after the end of treatment. The analyses evaluated the changes in mRNA levels of some renin-angiotensin system (RAS) related genes: angiotensinogen, renin, angiotensin-converting enzyme (ACE) and angiotensin II type 1 receptor (AT1) and vascular endothelial growth factor (VEGF), which can be related to ACE production, by RT-PCR. RESULTS: Renin was only observed in treated groups, TC+IR and IR, compared with the control group. ACE and VEGF levels were decreased in TC+IR (p<0.001) and in IR (p<0.001), and AT1 mRNA was higher in groups TC+IR (p<0.01) and IR (p<0.05) compared with the control group. CONCLUSION: Chemotherapy and irradiation can induce significant changes in some RAS related genes. These alterations are important to understand the pathways and consequences beyond cardiotoxicity induced by breast cancer treatments.

Up-regulation of angiotensin-converting enzyme and angiotensin II type 1 receptor in irradiated rats.

PURPOSE: To investigate changes in cardiac functional parameters and the cardiac expression of angiotensin-converting enzyme (ACE), angiotensin II type 1 receptor (AT1), procollagen type I (proc-I) and transforming growth factor-ß1 (TGF-ß1) in rats irradiated at heart. MATERIAL AND METHODS: Male Wistar rats were irradiated with a single dose of radiation (0, 5, 10 and 15 Gray [Gy]) delivered directly to the heart and the molecular evaluations were performed at various times post-irradiation (two days, 15 days and four months). The expression of ACE, AT1, proc-I and TGF-ß1 were analysed using Real Time-Polymerase Chain Reaction (RT-PCR) and/or Western blotting. Cardiac structural and functional alterations were investigated at the four-month time point by echocardiography and by quantitative methods (stereology). RESULTS: Rats irradiated with 15 Gy showed a modest reduction in the ejection fraction. Cardiac proc-I, TGF-ß1, ACE and AT1 were also measurably increased. CONCLUSIONS: Irradiated rat hearts show simultaneous elevations in renin-angiotensin system components AT1 and ACE and cardiac remodeling markers proc-I and TGF-ß1.