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Biomedical subjects

L Errazquin

Publications and source records attributed to L Errazquin.

8 recordsLinked to original sources
PubMed2001

A Monte Carlo approach for small electron beam dosimetry.

BACKGROUND AND PURPOSE: In treatments where it is necessary to conform the field shape yielding a very small effective beam area, dosimetry and conventional treatment planning may be inaccurate. The Monte Carlo (MC) method can be an alternative to verify dose calculations. A conjunctival mucosa-associated lymphoid tissues lymphoma is presented, to show the importance of an independent assessment in critical situations. MATERIALS AND METHODS: In this work, the MC technique has been employed using the program BEAM (based on EGS4 code). Electron beam simulation has been performed and the results have been compared with those obtained with films. The patient dose distribution has been obtained by two methods: the full Monte Carlo (FMC) simulation and a conventional planning system (PLATO). RESULTS: Concerning dosimetry, some differences have been observed in the comparison of profiles obtained with film and those obtained with the MC method. Moreover, significant differences were found in the patient isodose distribution between both calculation methods. CONCLUSIONS: The results highlight that, in treatments where small beams are needed, conventional dosimetry and planning systems have some limitations. Therefore, an independent and more accurate assessment, such as MC, would be desirable.

Computer Simulation↗
PubMed1997

Computer-based anthropometrical system for total body irradiation.

For total body irradiation (TBI) dose calculation requirements, anatomical information about the whole body is needed. Despite the fact that video image grabbing techniques are used by some treatment planning systems for standard radiotherapy, there are no such systems designed to generate anatomical parameters for TBI planning. The paper describes an anthropometrical computerised system based on video image grabbing which was purpose-built to provide anatomical data for a PC-based TBI planning system. Using software, the system controls the acquisition and digitalisation of the images (external images of the patient in treatment position) and the measurement procedure itself (on the external images or the digital CT information). An ASCII file, readable by the TBI planning system, is generated to store the required parameters of the dose calculation points, i.e. depth, backscatter tissue thickness, thickness of inhomogeneity, off-axis distance (OAD) and source to skin distance (SSD).

Anthropometry↗
PubMed1997

Lateral scatter correction algorithm for percentage depth dose in a large-field photon beam.

Differences between the scatter conditions of dosimetry and treatment situation are more important in the case of large-field photon beams than in standard ones. In the former, the scattering volume is defined by the phantom cross section; in the latter, the radiation field size. Two factors should be considered: the thickness and the cross section of the phantom. Both of them have an effect on the Percentage Depth Dose (PDD) distribution. In a previous study we addressed the influence of backscatter thickness on dose delivered. The aim of this work is to measure the effect of cross section phantom on the PDD curves under our TBI treatment conditions. Results showed a strong dependence of the PDDs on this parameter. A semi-empirical expression has also been derived to calculate (within 0.5% uncertainty) the Lateral scatter Correction Factor (LCF). The model of LCF states a linear dependence on depth whilst slope of these curves depends exponentially on distance to the lateral surface. The algorithm is being applied to our practical Total Body Irradiation (TBI) procedure.

Algorithms↗
PubMed1994

Midline dose algorithm for in vivo dosimetry.

The high level of accuracy required in radiotherapy treatment dosimetry makes necessary good treatment quality control. The common way is the use of in vivo dosimetry equipment that allows the direct measurement of dose delivered to the patient. Control of homogeneity and constancy of the incident beam on the patient can be achieved directly by means of entrance dose measurement; however, control of dose delivered to tumours and internal organs is difficult because of the impossibility of a direct measurement. In this case calculations are made using external measurements (entrance and exit sides of the patient) to obtain the dose delivered. In this work, an algorithm that allows the real-time knowledge of midline dose as a function of thickness and entrance and exit doses coming from semiconductor detectors is presented. By having the electrometer connected to the computer, these three values (entrance, midline, and exit dose) are displayed instantaneously when the algorithm is included in the acquisition program. The model has been developed both for standard (source to surface distance = 100 cm) and special treatment techniques such as total body irradiation (SSD = 314 cm). There is a good agreement of experimental and calculated values with differences below 0.04%.

Algorithms↗
PubMed1993

Backscatter correction algorithm for TBI treatment conditions.

The accuracy requirements in target dose delivery is, according to ICRU, +/- 5%. This is so not only in standard radiotherapy but also in total body irradiation (TBI). Physical dosimetry plays an important role in achieving this recommended level. The semi-infinite phantoms, customarily used for dosimetry purposes, give scatter conditions different to those of the finite thickness of the patient. So dose calculated in patient's points close to beam exit surface may be overestimated. It is then necessary to quantify the backscatter factor in order to decrease the uncertainty in this dose calculation. The backward scatter has been well studied at standard distances. The present work intends to evaluate the backscatter phenomenon under our particular TBI treatment conditions. As a consequence of this study, a semi-empirical expression has been derived to calculate (within 0.3% uncertainty) the backscatter factor. This factor depends lineally on the depth and exponentially on the underlying tissue. Differences found in the qualitative behavior with respect to standard distances are due to scatter in the bunker wall close to the measurement point.

Algorithms↗
PubMed1990

Clinical results of TBI for bone marrow transplantation at Sevilla.

We report on a series on 81 patients affected with acute leukemia undergoing TBI prior to BMT. An analysis of the achieved results is given, emphasizing the limited incidence of interstitial pneumonitis in our patients (3.7%). A suitable patient selection and treatment technique is also needed.

Acute Disease↗