Characteristics of a tandem system of ionization chambers in X-ray beams, mammography level.

Two parallel plate ionization chambers (inserted in slab phantoms) recently assembled at IPEN were studied in relation to their operational characteristics for use in quality control of X-ray beams, mammography level. The chambers present only one difference: one has an inner collecting electrode made of graphite and the other, of aluminum. These chambers make up a tandem system, which may be employed to verify X-ray beams energy constancy, by the confirmation of half-value layers and effective energies, and to determinate air kerma rates. The chambers presented good results for the operational tests, as recommended internationally.

Evaluation of subject contrast and normalized average glandular dose by semi-analytical models.

In this work, two semi-analytical models are described to evaluate the subject contrast of nodules and the normalized average glandular dose in mammography. Both models were used to study the influence of some parameters, such as breast characteristics (thickness and composition) and incident spectra (kVp and target-filter combination) on the subject contrast of a nodule and on the normalized average glandular dose. From the subject contrast results, detection limits of nodules were also determined. Our results are in good agreement with those reported by other authors, who had used Monte Carlo simulation, showing the robustness of our semi-analytical method.

Preliminary study of human breast tissue using synchrotron radiation combining WAXS and SAXS techniques.

Using synchrotron radiation, we combined simultaneously wide angle X-ray scattering (WAXS) and small angle X-ray scattering (SAXS) techniques to obtain the scattering profiles of normal and neoplastic breast tissues samples at the momentum transfer range 6.28 nm(-1)

Application of a wrist dosimeter prototype for radiation monitoring ((153)Sm) during a therapeutic procedure simulation.

Gamma and beta radiation emitting radiopharmaceuticals are handled in nuclear medicine services, and in many cases there is only individual monitoring of gamma radiation. In this paper, the results obtained using a wrist dosimeter prototype (CaSO(4):Dy+Teflon pellets) show that the doses for workers occupationally exposed to beta radiation from (153)Sm are not negligible. It is important that this dose is evaluated, and it has to be taken into consideration in the individual monitoring system.

Performance of a prototype of an extrapolation minichamber in various radiation beams.

An extrapolation minichamber was developed for measuring doses from weakly penetrating types of radiation. The chamber was tested at the radiotherapeutic dose level in a beam from a (90)Sr+(90)Y check source, in a beam from a plane (90)Sr+(90)Y ophthalmic applicator, and in several reference beams from an X-ray tube. Saturation, ion collection efficiency, stabilization time, extrapolation curves, linearity of chamber response vs. air kerma rate, and dependences of the response on the energy and irradiation angle were characterized. The results are satisfactory; they show that the chamber can be used in the dosimetry of (90)Sr+(90)Y beta particles and low-energy X-ray beams.

Use of composites of topaz-glass as TSEE and TL dosemeters.

The properties of the thermally stimulated exoelectron emission (TSEE) and thermoluminescent (TL) emission of topaz-glass composites were studied with the aim of using them as solid-state dosemeters. The TSEE response was studied as a function of radiation energy and as a function of absorbed dose. Topaz-glass composites presented a linear TL and TSEE response to dose within a range of 0.01-1 Gy. The topaz-glass composites presented higher TSEE peaks than topaz-Teflon pellets. In the dosimetry of radiotherapic fields normally the responses of the topaz-glass dosemeters are comparable to topaz-Teflon pellets. The results confirmed that these new dosemeters can be useful in monitoring the quality of the radiation sources. This dose mapping technique is particularly useful in investigating dose distribution throughout a planned target volume.

A special ionisation chamber for quality control of diagnostic and mammography X ray equipment.

A quality control program for X ray equipment used for conventional radiography and mammography requires the constancy check of the beam qualities in terms of the half-value layers. In this work, a special double-faced parallel-plate ionisation chamber was developed with inner electrodes of different materials, in a tandem system. Its application will be in quality control programs of diagnostic and mammography X ray equipment for confirmation of half-value layers previously determined by the conventional method. Moreover, the chamber also may be utilised for measurements of air kerma values (and air kerma rates) in X radiation fields used for conventional radiography and mammography. The chamber was studied in relation to the characteristics of saturation, ion collection efficiency, polarity effects, leakage current, and short-term stability. The energy dependence in response of each of the two faces of the chamber was determined over the conventional radiography and mammography X ray ranges (unattenuated beams). The different energy response of the two faces of the chamber allowed the formation of a tandem system useful for the constancy check of beam qualities.

Commercial glass for high doses using different dosimetric techniques.

Glass samples were tested for use in high-dose dosimetry in radiation processing. The main dosimetric characteristics were determined: lower detection threshold, reproducibility, response to gamma radiation of 60Co and thermal decay at room temperature, with the use of a densitometer, spectrophotometer and thermoluminescence reader. The results show that this kind of material could be useful for dosimetry in several applications of ionising radiation, taking into account its thermal fading.

Performance of pellets and composites of natural colourless topaz as radiation dosemeters.

The aim of the present work is to investigate the possibility of using the properties of the thermoluminescent emission (TL) of Brazilian natural topaz for dosimetric applications. Topaz is an aluminium fluorsilicate with general composition of Al2(SiO4)(F,OH)2 found with relative abundance in Brazil and in other parts of the world. Topaz from Santo Antonio do Jacinto, Minas Gerais. Brazil, was used in this work, in the form of pellets of topaz mixed with Teflon and composites made with topaz embedded in a glass matrix. The TL sensitivity was tested between 10(-4) and 10(4) Gy. The TL peak intensity increases with the dose before saturation, which occurs around 2 kGy. The peak intensity showed a strong dependence with radiation energy. The effect of visible light and the behaviour of the TL signals after successive irradiation-reading-annealing cycles are presented and discussed.

Dosimetric characterisation of Brazilian natural stones using the thermally stimulated exoelectron emission technique.

A thermally stimulated exoelectron emission (TSEE) measuring system developed and constructed at IPEN was used to verify the feasibility of the use of Brazilian natural semi-precious stones, such as jasper. amethyst, agate (blue and rose) and quartz (rose and white) for gamma and X radiation detection. Its counting system consists of a 2pi windowless gas-flow proportional counter, and the heating system is formed by a temperature programmer that provides linear heating of the samples. The samples were tested in gamma and in X radiation beams and evaluated in relation to their main dosimetric characteristics, as TSEE glow curves, calibration curves and energy dependence. The TSEE results are compared with those of thermoluminescence. The results obtained show the usefulness of Brazilian natural stones as dosimetric materials, using the thermoluminescence and thermally stimulated exoelectron emission techniques.

Influence of thermal treatments on the response decay of glass radiation detectors.

Commercial transparent glass has received attention in relation to its use as a gamma radiation detector. This kind of material presents a strong post-irradiation thermal decay at room temperature, which is a problem for high dose dosimetry purposes. This effect may be avoided by taking measurements always at the same time after irradiation of the glass samples. However, in this work effort has been given to this material characteristic, submitting the glass samples to different thermal treatments. The best results were obtained with a post-irradiation treatment at 130 degrees C during 10 min. This procedure seems to destroy the unstable entities responsible for the initial strong decay of the sample response, showing acceptable stability as a function of room temperature storage time.

Calibration of kVp meters used in quality control tests in diagnostic radiology by spectrometry.

A non-invasive calibration methodology of quality control instruments for diagnostic radiology was established and applied to different kinds of commercial kVp meters. The method uses the measurement of the spectrum endpoint as a reference. The results showed a variation of 10% between the responses of the instruments calibrated and the spectrometric system, a fact that demonstrates the need for instrument calibration.

Characterization of Al2O3 sintered pellets for dosimetric applications in radiotherapy.

Al2O3 sintered pellets were tested in relation to their thermoluminescent properties, to investigate the possibility of their use for dosimetry in the radiotherapy cases of 60Co and x-radiation. The material is inexpensive and has a glow peak at about 280 degrees C, a linear dose response between 0.1 and 100 Gy, suitable reproducibility and a low detection limit. The thermoluminescent response can easily be corrected for fading and the energy dependence, when necessary.

Induced effects in ionization chamber cables by photon and electron irradiation.

Photon and electron irradiation effects in cables and connectors of ionization chambers were investigated under different experimental conditions by means of measurements of the chamber response to a 90Sr standard check source and by measurements of radiation-induced leakage current. Correction factors for irradiation effects on cables and connectors were obtained as a function of the radiation energy, cable length, and absorbed dose dependences.

Absorbed dose dependence of the correction factors for ionization chamber cable irradiation effects.

A simple method was developed, for possible use by hospital physicists, to evaluate the irradiation effects on cables and connectors during large-radiation-field dosimetry with ionization chambers and to determine correction factors for the used system or geometry. This method was based on the absorbed dose dependence of the correction factor.