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Biomedical subjects

B E Bjarngard

Publications and source records attributed to B E Bjarngard.

13 recordsLinked to original sources
PubMed1988

Design and characteristics of a facility for total-body and large-field irradiation.

A facility for total-body X ray irradiation has been built using two 4 MV linear accelerators, one supported from the ceiling and one placed in a floor pit. The maximum distance between the sources is 410 cm. The patient lies supine on a light, movable support with a stretched-canvas top, halfway between the sources where the field size is 80 X 220 cm2. A special flattening filter maintains the doserate variation in air within +/- 3% over the central 70 X 200 cm2 of the field, but some quality variations within the beam are noticeable. The doserate at 205 cm distance from the sources is variable between 0.05 and 0.8 Gy/min (half from each source). To permit treatment of large fields at higher doserates, the accelerators can be moved vertically to place the sources at 120 cm or 160 cm from the patient's midplane. For this purpose, independently movable collimators are provided and the flattening filter is designed to provide two options, one for the large total-body field and the other with less filtration covering a smaller solid angle. At 120 cm distance, each beam can provide a doserate of up to 1.1 Gy/min.

Facility Design and Construction↗
PubMed1986

Scatter dose summation for irregular fields: speed and accuracy study.

Using program IRREG as a standard, we have compared speed and accuracy of several algorithms that calculate the scatter dose in an irregular field. All the algorithms, in some manner, decompose the irregular field into component triangles and obtain the scatter dose as the sum of the contributions from those triangles. Two of the algorithms replace each such component triangle with a sector of a certain "effective radius": in one case the average radius of the triangle, in the other the radius of the sector having the same area as the component triangle. A third algorithm decomposes each triangle further into two right triangles and utilizes the precalculated "equivalent radius" of each, to find the scatter contribution. For points near the center of a square field, all the methods compare favorably in accuracy to program IRREG, with less than a 1% error in total dose and with approximately a factor of 3-5 savings in computation time. Even for extreme rectangular fields (2 cm X 30 cm), the methods using the average radius and the equivalent right triangles agree to within 2% in total dose and approximately a factor of 3-4 savings in computation time.

Mathematics↗
PubMed1985

A test object for evaluation of portal films.

A test object has been designed for evaluation of the image quality of portal films in high energy photon radiation therapy. It consists of a pattern of notched polyvinyl chloride cylinders, fastened to a plastic sheet and immersed in water during exposure. In a pilot experiment, films produced with the test object were evaluated by a panel of observers. The results indicate that the use of the test object simulates the clinical application of portal films well. It is concluded that the test object can simplify studies of the efficacy of various methods to produce and view portal films.

Humans↗
PubMed1979

Magnification mammography: a low-dose technique.

Image quality and radiation exposures of a mammographic technique using direct radiographic magnification at 2 X with a microfocal spot x-ray tube and a fast, double screen-film system were compared to those of conventional contact mammography with a rare-earth screen and molybdenum target tube. The results indicate that the magnification technique yields improved detection of microcalcifications and comparable visualization of soft-tissue details, with a large reduction in radiation exposure. This technique has demonstrated the feasibility of carrying out high-quality mammography with an entrance dose of 1.35 X 10(-3) Gy (135 mrad) for the average breast.

Female↗
PubMed1979

Bremsstrahlung dose to patients in rotational electron therapy.

Dose and integral dose from bremsstrahlung in a 10-MeV electron beam were measured for irradiation of large areas with 120 degrees-arc rotational fields. The maximum bremsstrahlung dose ranged from 2% to 7% of the maximum electron dose for the different beam arrangements, while the integral dose showed the same range of variation. The concomitant bremsstrahlung beam should be collimated by the x-ray photon collimators and the use of narrow field rotations avoided.

Electromagnetic Phenomena↗
PubMedDate not supplied

Electron scattering and collimation system for a 12-MeV linear accelerator.

The original scattering and collimation system for the Siemens Mevatron XII linear accelerator used a lead scattering foil and box-type plastic collimators. This arrangement achieves excellent field flatness by repeated electron scattering. The electrons reaching the patient are widely distributed in energy and direction. This has detrimental effects on the depth-dose curves: slower falloff and increased surface dose. We have developed an alternative system for this accelerator, designed to minimize electron scatter and improve the safety of patient setup. Primary-electron scatter occurs in the bending-magnet exit window. Field uniformity is accomplished with a flattener of thin aluminum discs of different diameters, piled concentrically. An adjustable electron collimator 25 cm from the patient limits beam size, and a final electron collimator, either a cutout from lead sheet or a custom-made collimator of Lipowitz's metal, in contact with the patient, define the area to be treated. This design results in lower surface dose, sharper dose falloff, bremsstrahlung contamination less than or equal to 1%, and a field flatness expressed by a homogeneity index greater than 0.8 for large fields. Since there is no mechanical connection between the machine and the final collimator, the safety aspects of the system are considerably improved.

Electrons↗
PubMedDate not supplied

Head-scatter factors in rectangular photon fields.

Head-scatter factors were measured for a range of field sizes of rectangular shape from a linear accelerator that provides 6 and 25 MV photon beams. For a given field length and width, exchange of the inner and outer collimator pairs produces differences in the head-scatter factor of up to about 2% and 3% in open and wedged fields, respectively. Dependence on elongation deviates by up to 2% from that given by the equivalent squares. Such effects can easily be taken into account by using head-scatter data that have been directly measured in rectangular fields or by applying empirical corrections to values for square or equivalent square fields.

Biophysical Phenomena↗
PubMedDate not supplied

Dosimetry of 125I sources in a low-density material using scaling.

One may apply O'Connor's scaling theorem to dose measurements with brachytherapy sources in order to overcome the difficulties associated with the need for high spatial accuracy. This possibility has been evaluated by measuring the dose distribution around 125I sources in a low-density styrofoam phantom and comparing it with the dose distributions in water and solid water. Some generalization of the scaling theorem is proposed to allow for the minor differences in atomic composition between styrofoam and water, and the distances are scaled according to the ratio of the linear attenuation coefficients, instead of the physical densities, of the two media. The validity of this application of the scaling theorem has also been tested using Monte Carlo calculations. The results indicate that the scaling of the styrofoam measurements to water is a useful approximation in brachytherapy dosimetry.

Brachytherapy↗