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Biomedical subjects

A Brahme

Publications and source records attributed to A Brahme.

8 recordsLinked to original sources
PubMed1979

Absorbed dose from secondary electrons in high energy photon beams.

The absorbed dose in high energy photon beams due to scattered electrons from the irradiated air volume and from beam-shaping platforms has been calculated using the Fermi-Eyges theory of multiple scattering. The results are presented as lateral surface absorbed dose distributions across the field for three different radiation qualities, namely 60Co, 6 MV and 21 MV X-rays. For 60Co the relative absorbed dose due to electrons expelled in air reaches a value as high as 30% of the absorbed dose at dose maximum at a field size 40 X 40 cm2 and an SSD of 100 cm. The absorbed dose from electrons emanating from beam-shaping platforms contribute significantly to the absorbed dose at the surface when the platform is placed closer than 20--40 cm from the surface for field sizes greater than 10 X 10 cm2 to 40 X 40 cm2 respectively.

Electrons↗
PubMed1979

Radiation beam characteristics of a 22 MeV microtron.

The properties of the electron and photon beams from a 22 MeV clinical microton are presented. Favourable isodose distributions for radiation therapy are obtained for both modalities. For the electron beam this is accomplished using a dual scattering foil system in which the secondary foil is shaped to optimize uniformity and minimize energy loss and energy straggling. The photon beam is flattened by a composite filter to produce dose distributions of high uniformity over a wide depth interval.

Electrons↗
PubMed1979

Ferrous sulphate dosimetry for electrons. A re-evaluation.

A theory was developed for the perturbation correction to be applied in the calorimetric determination of the ferrous sulphate dosimeter G-value. Recent determinations of the molar extinction coefficient, epsilonm, have shown that systematic errors in epsilon may have influenced experimental G-values. With precision spectrophotometers this error is cancelled in the product epsilonm.G. It was shown that after applying the perturbation correction a very small spread was obtained in calorimetric epsilonm.G-values; the standard error of the mean being 0.2 per cent. The mean G-value is 2.3 per cent lower than that recommended in ICRU Report No. 21.

Absorption↗
PubMed1977

A 22 MeV microtron for radiation therapy.

The first 22 MeV micron installation for radiation therapy is described with regard to the general design, the beam transport and the gantry. The first measurements of the electron depth dose curves indicate that the distributions obtained are superior to those of most betatrons and linear accelerators. For the same electron beam energy the depth of dose maximum and the 90 or 80 per cent dose level is considerably increased. The 20.9 MV photon beam has similar depth dose characteristics as a 20 MV betatron.

Electrons↗
PubMed1975

Electron depth absorbed dose distribution for a 10 MeV clinical microtron.

Central axis depth absorbed dose distributions of the electron beam from a medical microtron accelerator have been measured. The measured distributions differ from those of existing betatrons and linear accelerators. A larger absorbed dose build-up and a sharper dose fall-off are obtained in close agreement with theoretical calcuations for monoenergetic electron beams. The differences from other accelerators are explained by the narrow energy spectrum, the clean geometry and the small amount of scattering material in the electron beam of the microtron.

Electrons↗
PubMedDate not supplied

Specification of electron beam quality from the central-axis depth absorbed-dose distribution.

The distribution of absorbed dose in a medium irradiated by broad electron beam has been analyzed from physical and therapeutic points of view. A number of parameters which describe the beam quality and the shape of the absorbed-dose distribution along the central axis are defined. Several comparisons are made of the values of these parameters obtained from measurements made on different therapy accelerators and from theoretically calculated dose distributions for monoenergetic and monodirectional beams. It is found that the major part of the observed differences between experimental and theoretical results can be attributed to the energy distribution of the accelerator beam and to processes in the scattering material, such as energy straggling and the production of secondary electrons and photons. A simple expression is derived relating the slower falloff in dose found for most accelerator beams to the large energy spread found in these beams. Further, a semiempirical relationship is found which makes it possible to obtain the mean electron energy at the phantom surface from the depth where the absorbed dose has decreased to 50% of its maximum value along the central axis.

Electrons↗