Biomedical subjects

H Huizenga

Publications and source records attributed to H Huizenga.

29 records · Page 2Linked to original sources

PubMed1994

Numerical calculation of energy deposition by high-energy electron beams: III. Three-dimensional heterogeneous media.

The phase space time evolution model of Huizenga and Storchi and Morawska-Kaczyńska and Huizenga has been modified to accommodate calculations of energy deposition by arbitrary electron beams in three-dimensional heterogeneous media. This is a further development aimed at the use of the phase space evolution model in radiotherapy treatment planning. The model presented uses an improved method to control the evolution of the phase space state. This new method results in a faster algorithm, and requires less computer memory. An extra advantage of this method is that it allows the pre-calculation of information, further reducing calculation times. Typical results obtainable with this model are illustrated with the cases of (i) a 20 MeV pencil beam in a water phantom, (ii) a 20 MeV 5 x 5 cm2 beam in a water phantom containing two air cavities, and (iii) a 20 MeV 5 x 5 cm2 beam in a water phantom containing an aluminium region. The results of the dose distribution calculations are in good agreement with and require significantly less computation time than results obtained with Monte Carlo methods.

Algorithms↗

PubMed1993

Quality assurance using portal imaging: the accuracy of patient positioning in irradiation of breast cancer.

PURPOSE: To study the accuracy of patient positioning in irradiation of breast cancer. METHODS AND MATERIALS: Megavolt portal images were obtained using a fast electronic megavoltage radiotherapy imaging system in 17 breast cancer patients immobilized with plastic fixation masks on a flat board with arm support and in 14 patients positioned without a mask on either a flat or a wedge-shaped board. Quantitative analysis of 510 megavolt portal images and comparison to 66 digitized simulation films was performed. Differences between the positioning techniques were evaluated. RESULTS: For the position of the patient in the field, standard deviations of the difference between simulation and treatment images were 3.2 mm and 4.6 mm for irradiation with and without masks, respectively. Larger standard deviations were found for the field width and length (5-7 mm), for collimator rotation (1.5-2 degrees), and for the position of the lung shielding block for patients positioned on the flat board (10-16 mm). The changes in field size and collimator rotation appeared to be largely due to the inclination of the technologists to slightly adapt fields in order to obtain a seemingly better congruity of the field with the skin or mask markings. Comparison of the accuracy of patient positioning with and without masks yielded similar error rates; standard deviations and extremes tended to be somewhat larger in positioning without a mask. The wedge-shaped board was preferred because of the ease of patient set-up and because the use of a lung block is avoided. The transition from simulation to treatment set-up yielded larger deviations than repeated treatment set-ups. CONCLUSION: These results emphasize again the continuous need for focusing attention on the accuracy of patient positioning in order to achieve maximal precision in radiotherapy. The electronic portal imaging system is very suitable for both quick on-line treatment verification and off-line analyses.

Breast Neoplasms↗

PubMed1993

Possible leakage radiation during malfunctioning of a Sagittaire accelerator.

A non-fatal accident with a CGR-Sagittaire accelerator in the Dr Daniel den Hoed Cancer Center (DDHCC) in Rotterdam in 1988 is described. In a period with frequently occurring technical problems, a patient, undergoing fractionated treatment at this accelerator for prostatic cancer, developed severe skin reactions on the right half ventral part of thorax, head and upper arm. The skin reactions suggested an irradiation with a dose of up to 10-20 Gy, so it was likely that a radiation accident had occurred caused by leakage radiation. A number of experiments were performed in attempting to explain the estimated large dose rates of leakage radiation. Under rather extreme malfunctioning conditions, a high leakage dose rate (4 Gy/min) could be obtained during therapy use. This condition might have occurred during this period of technical difficulty.

Accidents↗

PubMed1992

Isolation and partial characterization of a surface glycoconjugate of Entamoeba histolytica.

To study surface molecules of Entamoeba histolytica we produced monoclonal antibodies from mice immunized with lysates from the pathogenic amebic strain HM1:IMSS, and screened them for the ability to inhibit E. histolytica adhesion. One monoclonal antibody, CC 8.6, was a potent inhibitor of amebic adhesion to a Chinese hamster ovary cell line, and was capable of inhibiting HM1:IMSS mediated cytotoxicity by 50%. We found that monoclonal antibody CC 8.6 bound to an amebic glycoconjugate. The glycoconjugate is present only in E. histolytica and not in other Entamoeba sp. It migrates as a polydisperse band on SDS-PAGE, and can be metabolically radiolabeled with [14C]glucose, [32P]phosphate, and [3H]palmitate. The glycoconjugate can be purified by hydrophobic interaction chromatography on octyl-Sepharose; enzymatic hydrolysis with phosphatidylinositol-specific phospholipase C alters the hydrophobic properties of the molecule. HPLC analysis of [14C]glucose-labeled glycoconjugate saccharides revealed that approximately 82% of the incorporated label was in glucose and 12% in galactose. Our studies demonstrate that one of the immunogenic surface molecules of E. histolytica is a phosphorylated, lipid-containing, glycoconjugate, and that antibodies to this antigen may have the potential to protect against E. histolytica adhesion and cytotoxicity.

Animals↗

PubMed1991

Three-dimensional dose distribution of tangential breast treatment: a national dosimetry intercomparison.

From August 1990 to February 1991, a dosimetry intercomparison of breast treatment was performed at all 21 radiotherapy centres in The Netherlands. The absorbed dose was measured in three planes in a breast phantom during tangential breast irradiation, according to a prescribed technique. The beam energy could be chosen by the radiotherapy centre as normally applied for this type of "patient", and varied between 60Co and 8 MV X rays. The dose measured by the visiting team in 22 points inside the phantom was compared with the dose calculated by the institution using their local treatment planning system. In the institutions the mean ratio (the mean value of the ratios of the absolute calculated dose and the measured absolute dose in the 22 points) varied between 0.92 and 1.08 with an overall mean ratio of 1.04. There was no significant difference in this ratio between the three planes in a particular institution. In the isocentre the mean ratio of calculated and measured dose was 1.021 with a SD of 0.028, i.e. the algorithms in the six different commercial treatment planning systems calculate the dose generally somewhat too high. In order to explain the results, a measurement of the output under reference conditions was performed at each treatment unit. The mean ratio of the dose stated by the institution and the dose measured by the visiting team was 1.011 with a SD of 0.015 with a maximum deviation of 0.040. This small deviation explains therefore only part of the variation in the ratio of calculated and measured dose for tangential breast irradiation.(ABSTRACT TRUNCATED AT 250 WORDS)

Breast Neoplasms↗

PubMed1990

Performance of a prototype fluoroscopic radiotherapy imaging system.

An increasing demand exists for the implementation of radiotherapy imaging during routine patient treatment, not only for quality assurance of field alignment, but also to obtain full documentation of the actual radiation treatments given. As the method using conventional portal films has distinct disadvantages, alternative methods are required which preferably are faster and produce images of better quality. This paper describes the performance of a prototype fluoroscopic system in terms of spatial resolution and contrast resolution as well as imaging of patients during routine treatments. The system described appears to be suitable for patient set-up and treatment verification and documentation.

Equipment Design↗

PubMed1990

Film dosimetry of clinical electron beams.

Film dosimetry is used widely to obtain relative dose distributions of clinical electron beams in phantoms. Nevertheless, measurement results obtained with film dosimetry may lack precision and reliability. In this paper well defined and reproducible methods in film dosimetry are discussed. By application of these methods, film dosimetry appears to be adequate in measuring relative dose distributions of clinically applied electron beams, with an accuracy of 1% to 2% of the dose maximum, in water and plastics as well as in heterogeneously composed material.

Electrons↗

PubMed1989

Numerical calculation of energy deposition by broad high-energy electron beams.

The feasibility is demonstrated of a numerical method to calculate dose deposition by broad high-energy electron beams in homogeneous matter or in heterogeneous matter in which the heterogeneities are arranged in slabs perpendicular to the beam axis. The method is based only on the basic physical interaction processes of high-energy electrons and matter. The method is an extended version of the phase space time evolution method as described by Cordaro and Zucker (1971). The calculated depth-dose curves, energy spectra and angular distributions agree very well with results of the extensive class II Monte Carlo calculations of Andreo and Brahme (1984) and Andreo (1985), but require much less computer time: typically 3 minutes on a VAX 785 with floating point accelerator. This demonstrates the power of a numerical method in comparison with Monte Carlo methods.

Electrons↗

PubMed1988

Accuracy in radiation field alignment in head and neck cancer: a prospective study.

A prospective study has been performed to determine the accuracy of radiation field alignment for a group of 22 patients with tumors in the head and neck. The accuracy was assessed by an analysis of 138 megavolt portal films in comparison to 55 simulation films. The distance (at the patient midplane) between corresponding points at the field edges on verification film and simulation film appeared to be 5 mm on the average and the standard deviation 5 mm. The analysis was extended by translational and rotational matching of the fields in order to separate each error in a translation error of the field with respect to the patient and an error in field size or shape. Translation errors appear to be somewhat larger than field size or shape errors. From an analysis of a series of megavolt films taken every third radiotherapy session, it was concluded that treatment-to-treatment variations are as large as the errors due to the transition from simulation to treatment situation. Further analysis showed that variation of the patient's position within the cast is clearly one of the error sources.

Head and Neck Neoplasms↗

PubMed1987

The in-air scattering of clinical electron beams as produced by accelerators with scanning beams and diaphragm collimators.

The electron distribution F(x, y, z, theta x, theta y) in air has been evaluated for a clinical electron beam emanating from a scanning beam accelerator in which the collimation of the beam is performed by means of diaphragm collimators. The multiple scattering theory of Fermi turns out to be adequate in describing this electron distribution. In this theory, the only parameter to be determined experimentally is the angular variance at the level of the collimator blocks. Generally, this angular variance features the same energy dependence as the angular scattering power and its value at an arbitrary energy can be derived from measuring the penumbra widths of off-axis profiles in air, at various distances beyond the collimator blocks. Then, the angular variance at the level of a secondary diaphragm collimator can be calculated, as well as off-axis profiles in air at arbitrary distances. In this way, the relative electron distribution at the surface of patients can be calculated easily. This in turn serves adequately as input to the calculation of patient dose distributions in radiation therapy planning.

Air↗

PubMedDate not supplied

The use of computed tomography numbers in dose calculations for radiation therapy.

Although corrections for 'beam hardening' and 'scattering' have been implemented in currently available CT scanners, systematic differences exist between a real CT image and an ideal, artefact-free and monochromatic image. The appearance and magnitude of these differences are discussed. Conversion to the ideal image, i.e. conversion from CT number to X-ray attenuation coefficient at diagnostic photon energies, turns out to be possible with an accuracy of 5 per cent. In order to use the CT 'density' information from patients, in clinical photon and electron beam dose calculations, conversions must be made from the X-ray attenuation coefficient at diagnostic energies to relevant high energy radiation interaction properties. These conversions turn out to be possible within an accuracy also of 5 per cent. These limited accuracies cause errors in the photon beam dose calculation of less than 1 per cent of the dose maximum and errors in electron beam dose calculations of less than 2 per cent of the dose maximum.

Humans↗