C. E. deAlmeida

Determination of absorbed dose in water at the reference point d(r0, theta0) for an 192Ir HDR brachytherapy source using a Fricke system.

A ring-shaped Fricke device was developed to measure the absolute dose on the transverse bisector of a Ir192 high dose rate (HDR) source at 1cm from its center in water, D(r0,θ0). It consists of a polymethylmethacrylate (PMMA) rod (axial axis) with a cylindrical cavity at its center to insert the Ir192 radioactive source. A ring cavity around the source with 1.5mm thickness and 5mm height is centered at 1cm from the central axis of the source. This ring cavity is etched in a disk shaped base with 2.65cm diameter and 0.90cm thickness. The cavity has a wall around it 0.25cm thick. This ring is filled with Fricke solution, sealed, and the whole assembly is immersed in water during irradiations. The device takes advantage of the cylindrical geometry to measure D(r0,θ0). Irradiations were performed with a Nucletron microselectron HDR unit loaded with an Ir192 Alpha Omega radioactive source. A Spectronic® 1001 spectrophotometer was used to measure the optical absorbance using a 1mL quartz cuvette with 1.00cm light pathlength. The PENELOPE Monte Carlo code (MC) was utilized to simulate the Fricke device and the Ir192 Alpha Omega source in detail to calculate the perturbation introduced by the PMMA material. A NIST traceable calibrated well type ionization chamber was used to determine the air-kerma strength, and a published dose-rate constant was used to determine the dose rate at the reference point. The time to deliver 30.00Gy to the reference point was calculated. This absorbed dose was then compared to the absorbed dose measured by the Fricke solution. Based on MC simulation, the PMMA of the Fricke device increases the D(r0,θ0) by 2.0%. Applying the corresponding correction factor, the D(r0,θ0) value assessed with the Fricke device agrees within 2.0% with the expected value with a total combined uncertainty of 3.43% (k=1). The Fricke device provides a promising method towards calibration of brachytherapy radiation sources in terms of D(r0,θ0) and audit HDR source calibrations.

The measurement of photoneutron dose in the vicinity of clinical linear accelerators.

In Brazil, the replacement of rather old cobalt and cesium teletherapy machines with high-energy (E > 10 MV) medical linear accelerators (linacs) started in the year 2000, as part of an effort by the Ministry of Health to update radiotherapy installations. Since then, the contamination of undesirable neutrons in the therapeutic beam generated by these high-energy photons has become an issue of concern when considering patient and occupational doses. The walls of the treatment room are shielded to attenuate the primary and secondary X-ray fluence, and this shielding is generally considered adequate also to attenuate neutrons. However, these neutrons are scattered through the treatment room maze and might result in a radiological problem at the door entrance, an area of high occupancy by the workers of a radiotherapy facility. This paper presents and discusses the results of ambient dose equivalent measurements of neutron using bubble detectors. The measurements were made at different points inside the treatment rooms, including the isocentre and the maze. Several radiation oncology centres, which are users of Varian Clinac or Siemens machines, have agreed to allow measurements to be taken at their facilities. The measured values were compared with the results obtained through the semi-empirical Kersey method of neutron dose equivalent calculation at maze entrances, with reported values provided by the manufacturers as well as values published in the literature. It was found that the measured values were below the dose limits adopted by the Brazilian Regulatory Agency (CNEN), requiring no additional shielding in any of the points measured.

Absorbed dose calculations in a brachytherapy pelvic phantom using the Monte Carlo method

Monte Carlo calculations of the absorbed dose at various points of a brachytherapy anthropomorphic phantom are presented. The phantom walls and internal structures are made of polymethylmethacrylate and its external shape was taken from a female Alderson phantom. A complete Fletcher‐Green type applicator with the uterine tandem was fixed at the bottom of the phantom reproducing a typical geometrical configuration as that attained in a gynecological brachytherapy treatment. The dose rate produced by an array of five 137Cs CDC‐J type sources placed in the applicator colpostats and the uterine tandem was evaluated by Monte Carlo simulations using the code penelope at three points: point A, the rectum, and the bladder. The influence of the applicator in the dose rate was evaluated by comparing Monte Carlo simulations of the sources alone and the sources inserted in the applicator. Differences up to 56% in the dose may be observed for the two cases in the planes including the rectum and bladder. The results show a reduction of the dose of 15.6%, 14.0%, and 5.6% in the rectum, bladder, and point A respectively, when the applicator wall and shieldings are considered. PACS number(s): 87.53Jw, 87.53.Wz, 87.53.Vb, 87.66.Xa

Estimation of the RBE of mammography-quality beams using a combination of a Monte Carlo code with a B-DNA geometrical model

The PENELOPE code is used to determine direct strand break yields corresponding to photons from a (60)Co source and 28 and 30 kV x-ray beams impacting on a B-DNA geometrical model, which accounts for five organizational levels of the human genetic material. Direct single, double and total strand break probabilities are determined in a liquid water homogeneous medium with 1.06 g cm(-3) density. The spectra produced by the x-ray beams at various depths in the phantom have been used to study the dependence of the damage yield on the depth. The relative biological effectiveness (RBE) is also estimated using the (60)Co radiation qualities as the reference. According to this work, the damage probabilities and thus the RBE are, within the uncertainties, similar for both x-ray energies and are independent of the depth into the phantom. Furthermore, the total strand break yield is invariant with respect to the energy of the incident photons. The RBE for low-energy x-ray beams determined here (1.3 ± 0.1) is lower than that reported by Kellerer, taking into account that he used a 200 kV radiation as the reference quality. However, our RBE values are consistent with those determined by Kühne et al (2005 Radiat. Res. 164 669-76), which used the same biological endpoint and reference quality as our study. Also, our RBE values are similar to those determined by Verhaegen and Reniers (2004 Radiat. Res. 162 592-9).

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-β1 (TGF-β1) 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-β1 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-β1, 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-β1.

The Influence of DNA Configuration on the Direct Strand Break Yield

Purpose. To study the influence of DNA configuration on the direct damage yield. No indirect effect has been accounted for. Methods. The GEANT4-DNA code was used to simulate the interactions of protons and alpha particles with geometrical models of the A-, B-, and Z-DNA configurations. The direct total, single, and double strand break yields and site-hit probabilities were determined. Certain features of the energy deposition process were also studied. Results. A slight increase of the site-hit probability as a function of the incident particle linear energy transfer was found for each DNA configuration. Each DNA form presents a well-defined site-hit probability, independently of the particle linear energy transfer. Approximately 70% of the inelastic collisions and ~60% of the absorbed dose are due to secondary electrons. These fractions are slightly higher for protons than for alpha particles at the same incident energy. Conclusions. The total direct strand break yield for a given DNA form depends weakly on DNA conformation topology. This yield is practically determined by the target volume of the DNA configuration. However, the double strand break yield increases with the packing ratio of the DNA double helix; thus, it depends on the DNA conformation.

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.

Caspase-3 activation and increased procollagen type I in irradiated hearts

The caspase-3-cleaved presence was evaluated in this study in the heart of irradiated rats, during the decline of ventricular function. Female Wistar rats were irradiated with a single dose of radiation (15 Gy) delivered directly to the heart and the molecular, histological and physiological evaluations were performed at thirteen months post-irradiation. The expressions of procollagen type I, TGF-ß1 and caspase-3-cleaved were analyzed using Western blotting. Cardiac structural and functional alterations were investigated by echocardiography and electron microscopy. In the irradiated group, the levels of procollagen type I, TGF-ß1 and caspase-3-cleaved are increased. Significant histological changes (degeneration of heart tissue and collagen deposition) and functional (reduced ejection fraction) were observed. Data suggest that the cardiac function decline after exposure to ionizing radiation is related, in part, to increased collagen and increased caspase-3-cleaved.

Establishment of radiation qualities for mammography according to the IEC 61267 and TRS 457

This article presents the technical conditions necessary to establish appropriate radiation qualities for the calibration of the dosemeters used in the mammography detectors in the Laboratório de Ciências Radiológicas (LCR) from the Universidade do Estado do Rio de Janeiro. Tests were conducted to evaluate the homogeneity of the radiation field, scattering, half-value layers and system stability. The calibration method (substitution) is described in this work. A moderate alteration in filtration makes it possible to maintain the half-value layers within the limits recommended. The results indicate the adequacy of the LCR laboratory for the calibration of the dosemeters in the radiation qualities for mammography with an expanded uncertainty in the best measurement capability of ± 1.8 % (k = 2).

The design of a new insert for calibration of LDR and HDR 192Ir sources in a well-type ionization chamber.

Some well-type ionization chambers, present a very small sweet spot that are sufficient for small HDR sources. However, if a longer HDR source or LDR wires are calibrated, the positional uncertainty increases and an approximated correction factor must be applied, resulting in an increased uncertainty. One of the ways to avoid this problem would be to flatten the well chamber response by increasing its sweet spot region. This work uses the Monte Carlo code PENELOPE to simulate the response of a well-type chamber HDR-1000, with its original insert, by using an HDR 192Ir source and proposes a new insert design that increases its flatness region from 1.0 cm to approximately 4.0 cm (+/- 2.0 cm about the peak response).