A portable Compton spectrometer for clinical X-ray beams in the energy range 20-150 keV.

Primary beam spectra were obtained for an X-ray industrial equipment (40-150 kV), and for a clinical mammography apparatus (25-35 kV) from beams scattered at angles close to 90°, measured with a CdTe Compton spectrometer. Actual scattering angles were determined from the Compton energy shift of characteristic X-rays or spectra end-point energy. Evaluated contribution of coherent scattering amounts to more than 15% of fluence in mammographic beams. This technique can be used in clinical environments.

Ambient dose equivalent and effective dose from scattered x-ray spectra in mammography for Mo/Mo, Mo/Rh and W/Rh anode/filter combinations.

In this study, scattered x-ray distributions were produced by irradiating a tissue equivalent phantom under clinical mammographic conditions by using Mo/Mo, Mo/Rh and W/Rh anode/filter combinations, for 25 and 30 kV tube voltages. Energy spectra of the scattered x-rays have been measured with a Cd(0.9)Zn(0.1)Te (CZT) detector for scattering angles between 30 degrees and 165 degrees . Measurement and correction processes have been evaluated through the comparison between the values of the half-value layer (HVL) and air kerma calculated from the corrected spectra and measured with an ionization chamber in a nonclinical x-ray system with a W/Mo anode/filter combination. The shape of the corrected x-ray spectra measured in the nonclinical system was also compared with those calculated using semi-empirical models published in the literature. Scattered x-ray spectra measured in the clinical x-ray system have been characterized through the calculation of HVL and mean photon energy. Values of the air kerma, ambient dose equivalent and effective dose have been evaluated through the corrected x-ray spectra. Mean conversion coefficients relating the air kerma to the ambient dose equivalent and to the effective dose from the scattered beams for Mo/Mo, Mo/Rh and W/Rh anode/filter combinations were also evaluated. Results show that for the scattered radiation beams the ambient dose equivalent provides an overestimate of the effective dose by a factor of about 5 in the mammography energy range. These results can be used in the control of the dose limits around a clinical unit and in the calculation of more realistic protective shielding barriers in mammography.

Comprehensive analysis of the spectrometric determination of voltage applied to X-ray tubes in the radiography and mammography energy ranges using a silicon PIN photodiode.

This work describes the analysis of factors which affect the results of estimation of the electron accelerating potential (kVp) applied to an X-ray tube, through determination of the end point of the energy spectrum of the emitted radiation beam. Measurements have been performed utilizing two spectrometers each with a silicon PIN photodiode: one operating at room temperature, and the other, a high resolution spectrometer, with a Peltier cooler. Both were directly irradiated by different X-ray beams. Both systems work at low voltage and without liquid nitrogen cooling, thus avoiding the drawbacks presented by germanium detectors. Each kVp value was determined by linear regression of the end of the spectrum, so as to give, simultaneously, the best fit to the experimental data and low standard deviation for the kVp value. Detector energy resolution and calibration, counting statistics and high voltage waveform ripple have been investigated in order to establish better experimental conditions and to optimize measurement time. Results of measurements carried out with X-ray tubes connected to single-phase, three-phase or constant potential units, using additional filtration of Cu, Al or Mo (for mammographic beams), are presented. The variations resulted in kVp uncertainties up to 0.1 kV.

Determination of the voltage applied to x-ray tubes from the bremsstrahlung spectrum obtained with a silicon PIN photodiode.

This work describes a methodology for the obtainment of the electron accelerating potential (kVp) applied to an x-ray tube, through the determination of the end point of the energy spectrum of the radiation emitted by the tube. The measurements have been performed utilizing alternatively two silicon PIN photodiodes, directly irradiated by the x-ray beam. Both were operated at room temperature, with low bias, so avoiding the drawbacks presented by photomultiplier tubes and germanium detectors. The energy calibration of the system was performed with X- and gamma-emitter radioactive sources, which makes the method absolute. Each kVp value was determined by means of a linear regression in the end of the spectrum, to give, simultaneously, a good fit of the straight line to the experimental data and a low standard deviation for the kVp value. Results of the measurements carried out with an x-ray tube connected to a three-phase generator, using additional filtration between 1.5 and 4.0 mm of Cu, are presented. This filtration was used in order to minimize the contribution of low energy photons and to reduce pulse pile-up. Errors determined for the values of kVp are between 0.06 and 0.16 kV, in the potential range from 50 to 100 kV. As an example, the methodology has been applied in the verification of the secondary calibration of a voltage divider, utilized, by its turn, in the tertiary calibration of noninvasive kVp meters. All intrinsic sources of errors involved in the process are discussed and evaluated.