This work is devoted to studying the influence of chamber response functions on the standard IMRT verification for the different detector technologies available on commercial devices. We have tested three of the most used 2D detector arrays for radiotherapy dosimetry verification, based on air-ionization chambers and diode detectors. The response function has been carefully simulated using the Monte Carlo method and measured through slit and pinhole collimators. Although the response function of air-ionization detectors is considerably different with respect to that of standard diodes, the impact on a verification based in the gamma function with tolerances 3 mm and 3% is quite limited. The results show that the standard air-ionization detector arrays perform in a similar way whenever the tolerances for the gamma function are not lowered below 1.5 mm and 1.5%. Additionally, the sensitivity of these devices to fluence perturbations was measured by intentionally modifying some leaf positions in the multileaf collimator. The wider response function of air-ionization chamber arrays made them slightly more sensitive to random fluence perturbations, although silicon diode arrays are more accurate to describe the dose distribution in a point by point basis.

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-The workers performing different activities with radionuclides in nuclear medicine centers are at potential risk of external exposure and internal contamination. The IAEA Safety Guide N• RS-G-1.2 proposed criteria for determining the need for a routine monitoring program to assess internal contamination. For this purpose, an Excel template containing the IAEA criteria was applied in three nuclear medicine centers in Chile. The results show that it is necessary to carry out a routine monitoring program for five workers who handle 131 I and three for 99m Tc. We propose to implement this template at a national level in order to improve the conditions of radiation protection in the participating centers.

Anthropomorphic phantoms are used in nuclear medicine for imaging quality control, calibration of gamma spectrometry system for the study of internal contamination with radionuclides and for internal dosimetric studies. These are constructed of materials that have radiation attenuation coefficients similar to those of the different organs and tissues of the human body. The material usually used for the manufacture of phantoms is polymethyl methacrylate. Other materials used for this purpose are polyethylene, polystyrene and epoxy resin. This project presents the design and manufacture of an anthropomorphic thyroid-neck phantom that includes the cervical spine, trachea and oesophagus, using a polyester resin (ρ = 1.1 g cm(-3)). Its linear and mass attenuation coefficients were experimentally determined and simulated by means of XCOM software, finding that this material reproduces the soft tissue ICRU-44 in a range of energies between 80 keV and 11 MeV, with less than a 5 % difference.

Different procedures have been used to develop x-ray fluorescence spectroscopy in Chile. In this paper we describe those groups doing basic or applied scientific research, mainly associated with units at universities and research centers. The techniques are PIXE, common XRF, XRF excited with gamma sources, x-ray emission from an electron microprobe and the total reflection technique. Historical aspects and experimental features are mentioned. Theoretical and methodological projects are also described. Finally, the wide field of applications of XRF in Chile is presented.

Purpose: Historically, beam matching of similar Linear Accelerators has been accomplished by sending beam data to the manufacturer to match at their factory. The purpose of this work is to demonstrate that fine beam matching can be carried out on‐site as part of the acceptance test, with similar or better results. Methods: Initial scans of a 10 × 10 Percent depth dose (PDD) and a 40 × 40 beam profile at the depth of Dmax, for 6MV and 10 MV were taken to compare with the standard beam data from the Versa. The energy was then adjusted and the beam steered to achieve agreement between the depth dose and the horns of the beam profile. This process was repeated until the best agreement between PDD and profiles was achieved. Upon completion, all other clinical data were measured to verify match. This included PDD, beam profiles, output factors and Wedge factors. For electron beams PDD's were matched and the beam profiles verified for the final beam energy. Confirmatory PDD and beam profiles for clinical field sizes, as well as Output Factors were measured. Results: The average difference in PDD's for 6MV and 10MV were within 0.4% for both wedged and open fields. Beam profile comparisons over the central 80% of the field, at multiple depths, show agreement of 0.8% or less for both wedged and open fields. Average output factor agreement over all field sizes was 0.4% for 6MV and 0.2 % for 10MV. Wedge factors agreement was less than 0.6% for both photon energies over all field sizes. Electron PDD agreed to 0.5mm. Cone ratios agreed to 1% or less. Conclusion: This work indicates that beam matching can be carried out on‐site simply and quickly. The results of this beam matching can achieve similar or better results than factory matching.

An algorithm based on fundamental parameters and applied to the SEICXRF method, developed by one of the authors, is presented. The methodology used in the calculation is similar to the Rousseau fundamental parameters method, but the main difference is the considerations about the x‐ray secondary fluorescence. In the new experimental method, the fluorescence yield by photons corresponding to the absorption edges with energies greater than the absorption edge energy of analyte does not occur. This secondary fluorescence appears in the calculation of the total fluorescence as a consequence of the integral count of the fluorescent emission from the sample. It is created by the primary fluorescence yield of the atoms whose absorption edge energies are less than the primary fluorescence energy of the analyte. The algorithm also considers the effect of the decrease of the sample fluorescent background just at the jump, originated by the change of the absorption coefficient at the absorption edge energy of the element of interest. Considering these two effects, including the primary fluorescence in the calculation, allows one to obtain the net fluorescence originated by the analyte at its own absorption edge. Copyright © 2003 John Wiley & Sons, Ltd.