Biomedical subjects

E el-Khatib

Publications and source records attributed to E el-Khatib.

21 records · Page 2Linked to original sources

PubMedDate not supplied

Calculation of dose profiles in homogeneous phantoms for irregular, partially attenuated, photon beams.

Measured and calculated dose profiles under partial attenuators which cover only part of the radiation beam are presented. The study was performed for x-ray beams generated with a 4-MV linear accelerator at a source-surface distance of 120 cm in a water phantom for lead attenuators of arbitrary shape but constant thickness. Dose correction factors, which are used to multiply the open beam data to predict doses under partial attenuators, depend strongly on attenuator parameters, such as its thickness, lateral dimensions, and distance from phantom or patient surface, in addition to depending on depths in the phantom. The dose correction factors are calculated with Clarkson sector integration techniques, and the results, in spite of the simplifying assumptions used in the algorithm, generally agree with measured data to within 3%. The calculational method therefore may be applied to general clinical situations in which partial attenuators are used.

Humans↗

PubMedDate not supplied

Evaluation of film and thermoluminescent dosimetry of high-energy electron beams in heterogeneous phantoms.

Film and thermoluminescent dosimetry (TLD) are investigated in heterogeneous phantoms irradiated by high-energy electron beams. Both film and TLD are practical dosimeters for multiple and moving beam radiotherapy. The accuracy and precision of these dosimeters for radiation dose measurements in homogeneous water-equivalent phantoms has been discussed in the literature. However, film and TLD are often used for dose measurements in heterogeneous phantoms. In those situations perturbations are produced which are related to the density and atomic number of the phantom material and the physical size and orientation of the dosimeter. In our experiments the relative dose measurements in homogeneous phantoms were the same regardless of dosimeter or dosimeter orientation. However, significant differences were observed between the dose measurements within the inhomogeneity. These differences were influenced by the type and orientation of the dosimeter in addition to the properties of the heterogeneity. These differences could be reproduced with Monte Carlo calculations and modeling of the experimental conditions.

Electrons↗

PubMedDate not supplied

Verification of a two-dimensional pencil beam arc electron dose calculation algorithm.

The dosimetry of arced electron beams is of increasing importance because of the increased capabilities of modern linear accelerators. A practical pencil beam algorithm has been developed for arc electron beams and is capable of using computed tomography information for heterogeneity corrections. For homogeneous phantoms, the maximum dose and bremsstrahlung components are predicted very accurately, that is, within 1% of the maximum dose. However, the depth of maximum dose (treatment depth) is predicted to be deeper than measurement, as much as 0.7 cm deeper. For a heterogeneous lung phantom, the discrepancies are as high as 30%, but the accuracy of dose calculation is consistent with conventional stationary pencil beam algorithms. It was concluded that improvements in the dose prediction are possible with more accurate calculations of the pencil beam widths and the incorporation of range straggling into the algorithm.

Algorithms↗