C. Ruiz-Trejo

Study of the TL response of LiF:Mg,Ti to 3 and 7.5 MeV helium ions: Measurements and interpretation in terms of the track interaction model

Abstract We have measured the LiF:Mg,Ti (TLD-100) thermoluminescent response, efficiency and supralinearity, to 3 and 7.5 MeV helium ions in the fluence interval between 6×107 to 1.5×1011 cm−2. Ion irradiations were performed using a flux of elastically scattered ions from a thin gold target. The measured efficiencies with respect to 60Co γ-rays are equal to 0.074 and 0.174 at 3 and 7.5 MeV, respectively, for the response of peak 5. The supralinearity functions for peaks 4, 5, 6a, 6b, 7, 8, 9 and the total TL signal indicate that supralinearity is an increasing function of energy and that it increases with peak temperature. The data for peaks 5, 8 and 9 have been successfully described by Monte Carlo simulations of the track interaction model. The fitted parameters show that peak 5 displays a special behaviour which requires the use of a much larger effective track radius than the higher temperature peaks.

Response of radiochromic dye films to low energy heavy charged particles

Abstract We have studied the possible use of radiochromic dye films (RCF) as heavy charged particle dosemeters. We present the results of irradiating two commercial RCF (GafChromic HD-810 and MD-55-1) with 1.5, 2.9 and 4.4 MeV protons, 1.4, 2.8, 4.7, 5.9, 6.8 MeV 4He ions and 8.5 and 12.4 MeV 12C ions, at proton doses from about 1 Gy up to 3 kGy, helium ions doses from 3 Gy to 5 kGy and carbon ion doses from 30 Gy to 20 kGy. The films were scanned and digitized using commercial equipment. For a given particle, the response per unit dose at different energies indicates an energy dependence of the sensitivity, which is discussed. Comparison was made for the use of a standard spectrophotometer to obtain optical density readings versus a white light scanner.

Supralinear response and efficiency of LiF:Mg,Ti to 0.7, 1.5 and 3 MeV protons

Abstract The thermoluminescent (TL) response, supralinearity function, and relative efficiency with respect to 60 Co γ-rays, of TLD-100 exposed to 0.7, 1.5 and 3 MeV protons have been measured. The TL response of the glow curve peaks using two different deconvolutions, separating in either 7 (3–9) or 9 peaks (3–10 and peaks 6a and 6b), was investigated. Results for the supralinearity function of peaks 5 and 7–9 and the relative response of peaks 5 and 7 are insensitive to the chosen deconvolution scheme. At all energies we observe that peak 5 is slightly supralinear and that supralinearity increases as a function of the peak temperature. The relative efficiencies, measured for the total TL signal (area under the glow curve) and peaks 5 and 7, decrease with the proton energy having values of 0.33, 0.46 and 0.70 (total TL signal), 0.22, 0.32 and 0.53 (peak 5) and 1.4, 2.6 and 3.6 (peak 7) at 0.7, 1.5 and 3 MeV, respectively. These data agree with the systematics reported in the literature. The measurements of the supralinearity function are compared with Monte Carlo track interaction model calculations. The analysis suggests that the model ion track effective radius and the saturation radius are independent of the incident ion energy.

Image quality and mean glandular dose in Mexican mammography services measured with an Object-Insert/TL mammography kit

Thirty mammography systems were evaluated using an Object-Insert/TL kit (composed of an image quality and a dosimetric phantom) to assess image quality and mean glandular dose. All systems complied with the minimum score for object visibility in the image phantom, but most of the images showed artifacts. The average of the mean glandular dose was 1.7±0.7 mGy, and three systems delivered doses higher than the 3 mGy reference value. A weak correlation was found between image quality and dose, possibly reflecting the lack of quality control in the evaluated equipment.

Computed Tomography: Image and Dose Assessment

In this work an experimental evaluation of image quality and dose imparted during a computed tomography study in a Public Hospital in Mexico City is presented; The measurements required the design and construction of two phantoms at the Institute of Physics, UNAM, according to the recommendations of American Association of Physicists in Medicine (AAPM). Image assessment was performed in terms the spatial resolution and image contrast. Dose measurements were carried out using LiF: Mg,Ti (TLD‐100) dosemeters and pencil‐shaped ionisation chamber; The results for a computed tomography head study in single and multiple detector modes are presented.

A Study on Dual‐Energy Subtraction in Digital Mammography

Experimental subtraction of phantom digital mammographic images obtained at 25 and 40 kVp Mo/Mo and Rh/Rh, normal and hardened beams, has been performed. Single energy attenuation measurements in human microcalcifications show a weaker absorption than expected from CaCO3 composition. Signal‐to‐noise ratios in the subtracted images have been compared with numerical calculations following Lemacks formalism, and qualitative agreement is obtained. The expected increase in contrast when the high voltage beam is hardened is observed in the measurements.

A Computerized Tomography Phantom: Design and Construction

A phantom for performance evaluation and quality assurance of CT scanners was designed and built in agreement with quality control requirements established by the Mexican Regulations (NOM‐158‐SSA1‐1996). Phantom materials were chosen after experimental determination of their Hounsfield units. The phantom allows to perform the following tests: calibration, constancy and uniformity of the CT number, CT number dependence on the reconstruction algorithm, high and low contrast resolution, slice thickness and coincidence of the slice with the light system for patient alignment. We present and discuss the results of these test applied to two CT scanners.

Mammographic image quality assessment in two public hospitals in Mexico City

We describe the protocol and preliminary results of a project aimed at assessing image quality and dose associated to mammographic studies produced in two public hospitals in Mexico City.