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Biomedical subjects

I Lax

Publications and source records attributed to I Lax.

104 records · Page 6Linked to original sources
PubMed1981

Electron beam dose planning using discrete Gaussian beams. Mathematical background.

A general method for computerized electron beam dose planning is proposed based on the use of a square or hexagonal grid or matrix of discrete Gaussian elementary beams. Using this method the distribution of absorbed dose in an electron beam of arbitrary cross-section incident on an irregular patient surface can be calculated taking the influence of tissue inhomogeneities into account. The derived expressions for the absorbed dose in narrow and broad uniform beams are compared with experimental data and Monte Carlo calculations. Good agreement is obtained over the clinically significant portion of the absorbed dose distribution at a fairly wide grid spacing of about 0.5 cm.

Computers↗
PubMed1980

Collimation of high energy electron beams.

The collimation of high energy electron beams for radiation therapy is treated with special attention on the contamination of the beam by electrons which ideally should be stopped, but instead are scattered back into the beam through the edge of the collimator. It is demonstrated that the mean energy of these electrons is only 40 per cent of the mean energy in the beam and that the smallest electron contamination is obtained if the material closest to the beam is of high density.

Mathematics↗
PubMed1978

Dose distribution in 42 MV roentgen irradiation of cervical carcinoma.

The dose distribution obtained with two different techniques for external irradiation of cervical carcinoma is described. The dose to the central area is somewhat higher with the multiple beam technique compared with the newly introduced shielding block technique. The difference between the calculated CRE values for the two techniques is small. When the shielding block is not placed over the area corresponding to the position of the applicators from the previous intracavitary treatment the considerable difference in absorbed dose between the two techniques does not correspond to the difference in the calculated CRE values. A comparison of the relative distributions laterally, in total dose and CRE, shows that for central volumes the relative CRE is much higher than the relative dose, when the normalization is made at the pelvic wall.

Absorption↗
PubMed1977

Electron therapy of intraorbital tumors.

The authors describe a modification of a previously reported method of treating intraorbital tumors using multiple electron beams. An adjustable metal shield is inserted in the electron tube to protect the lens. The three-dimensional dose distribution was determined by film measurements and the film density measured with an RFA-1 densitometer on line with a computer. The density values were stored in a three-dimensional matrix. Different planes in the matrix can be selected for isodose plotting.

Electrons↗
PubMed1977

Effect of radiation therapy on the mitogenic response of in vitro irradiated human lymphocytes to phytohaemagglutinin.

Irradiation of human peripheral lymphocytes in vitro reduces their capacity to be triggered to DNA-synthesis by PHA in a two-dose shaped fashion suggesting the presence of one relatively radiation sensitive and one relatively resistant cell population. Intracavitary and external radiation therapy for carcinoma of the uterus and vagina, which reduced the lymphocyte counts by approximately 66 per cent, did not significantly change the ratio of these subpopulations, indicating that PHA-reactive cells cannot be grouped into radiation sensitive and resistant subpopulations.

Cells, Cultured↗
PubMedDate not supplied

Synthetic peptide approach to the analysis of kinase activities of avian EGF receptor and v-erbB protein.

Analysis of the structure and function of a protein such as the epidermal growth factor receptor is facilitated by the use of antibodies directed against discrete portions of the protein. Here, we describe the characterization and use of antibodies directed against synthetic peptides corresponding to specific portions of the epidermal growth factor receptor and/or v-erbB protein. In particular, one useful antiserum has allowed us to compare the protein kinase activities of the epidermal growth factor receptor and the v-erbB proteins and to conclude that the v-erbB protein is a protein-tyrosine specific kinase as is its homologue the avian epidermal growth factor receptor.

Alpharetrovirus↗
PubMedDate not supplied

Amplification, enhanced expression and possible rearrangement of EGF receptor gene in primary human brain tumours of glial origin.

Epidermal growth factor (EGF), through interaction with specific cell surface receptors, generates a pleiotropic response that, by a poorly defined mechanism, can induce proliferation of target cells. Subversion of the EGF mitogenic signal through expression of a truncated receptor may be involved in transformation by the avian erythroblastosis virus (AEV) oncogene v-erb-B, suggesting that similar EGF receptor defects may be found in human neoplasias. Overexpression of EGF receptors has been reported on the epidermoid carcinoma cell line A431, in various primary brain tumours and in squamous carcinomas. In A431 cells the receptor gene is amplified. Here we show that 4 of 10 primary brain tumours of glial origin which express levels of EGF receptors that are higher than normal also have amplified EGF receptor genes. Amplified receptor genes were not detected in the other brain tumours examined. Further analysis of EGF receptor defects may show that such altered expression and amplification is a particular feature of certain human tumours.

Brain Neoplasms↗
PubMedDate not supplied

Electron beam dose planning using Gaussian beams. Energy and spatial scaling with inhomogeneities.

The penetration of an electron beam in matter is characterized by only two material dependent parameters within the range of validity of the small angle diffusion equation. These parameters characterize the relative importance of multiple scattering and energy loss for a given material and energy. By comparison with more accurate Monte Carlo calculations it is shown that the same two parameters can be used to scale the dose distribution from one material and energy to an equivalent energy in an arbitrary material with high precision also outside the limits of the small angle approximation. This scaling procedure has been generalized to the non-uniform case with plane parallel slab inhomogeneities by assuming the angular distribution on each side of the interfaces to be equal. The generalized recursive scaling procedure is finally tested by measurements on almost point monodirectional beams in water with inserted aluminum plates of varying thicknesses. The agreement with the scaling procedure is of the order of one per cent with regard to the radial dose profiles.

Electrons↗
PubMedDate not supplied

Stereotactic radiation therapy of intracranial lesions. Methodologic aspects.

A technique for stereotactic radiation therapy of cerebral tumours and arteriovenous malformations using a linear accelerator (6 MV photons) is proposed. Treatment relies on a fixation system that permits a precise use of the coordinates estimated at stereotactic angiography or stereotactic computed tomography. The field of treatment can be exactly outlined in the CT images during repeat examinations, thus facilitating the recognition of changes induced by radiation. The system also allows the extent of the arteriovenous malformation, as seen at angiography, to be accurately traced in the CT sections thus enabling evaluation of possible radiation damage to surrounding brain structures. The precision of the method as well as its hypothetical merits and disadvantages are discussed. The number of patients treated is still small and the follow-up time is too short in the majority of cases to allow definite conclusions. Examples of preliminary results are given.

Aged↗