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Biomedical subjects

J M Jensen

Publications and source records attributed to J M Jensen.

At least 55 records · Page 3Linked to original sources
PubMed1990

[The effect of the focal distance parameter on the dose rate of radiotherapy equipment].

In radiotherapy it is sometimes necessary to use nonstandard treatment distances, i.e. in mantle-field irradiation or in total-body irradiation. The design of the collimating system as well as other components of the treatment head are influencing the dose rate depending on focus-patient respectively focus-phantom distance (FPD). The quality of the collimator and the dependence on FPD, which deviates from the inverse-square law, were described by a new defined parameter INV. This parameter INV was checked experimentally on various treatment units. For approximation and explanation of this INV factor a combination of a point, line and area source is proposed.

Humans↗
PubMed1990

[Hyperfractionation--a new challenge for medical electron linear accelerators?].

In radiotherapy to an increasingly degree radiobiological aspects of the tumor behaviour during therapy are realized in daily routine. An example for this is the so called hyperfractionation of the total dose: that means multiple small fractions are applied. Doses of as low as circa 40 cGy per field are necessary. This investigation affects the constancy and the behaviour of the following beam parameters of various treatment units during the initial stage of operation (circa ten seconds): energy of bremsstrahlung, symmetry, flatness and proportionality of dose.

Electrons↗
PubMed1989

Periodic hyperammonemic encephalopathy associated with a ureterosigmoidostomy.

Ureterosigmoidostomy, a urinary diversion procedure performed for treatment congenital urologic defects or bladder cancer, may be associated with hyperammonemia. A delayed periodic encephalopathy, characterized by dysarthria, ataxia, and coma, developed in a 44-year-old woman who had undergone this procedure. Hyperammonemia-associated neurotoxicity resolved after surgical revision of the ureterosigmoidostomy to a uretero-ileostomy. Therefore, a treatable episodic encephalopathy may occur in association with hyperammonemia in patients who have undergone ureterosigmoidostomy.

Adult↗
PubMed1988

Does active rheumatoid arthritis affect intestinal iron absorption?

One of the causes of anaemia in rheumatoid arthritis is thought to be defective iron absorption. In this study the 59Fe absorption in patients with active rheumatoid arthritis is measured and correlated with the results for bone marrow iron stores (and in some cases with the iron stores in the terminal duodenum), which were assessed simultaneously with semiquantitative methods, and with the serum ferritin concentration. In 11 patients with rheumatoid arthritis and increased bone marrow iron stores, iron absorption was decreased. In five patients it was normal and in three further patients, whose bone marrow iron stores were depleted, iron absorption was maximally increased. According to the results both intestinal malabsorption and defective iron absorption can be excluded as causes.

Adult↗
PubMed1988

[Field-integrated dosage modification (FIDM). 2. The physical principles of the procedure].

A method is suggested and described which allows to introduce areas of different sizes, shapes, sites, and doses into a photon irradiation field. The bases for calculation and manufacturing of such irregular field stops containing integrated dose modification blocks are, according to precision requirements and data acquisition possibilities, either information provided by computed tomography or conventional planning radiographs. The following standard parameters are required as input data: sizes, shapes, and positions of the partial fields within the total irradiation field, depth of the reference plane, absorption coefficient of the modification material used, proportions of the planned dose modification, radiation quality, and other radiation field parameters. For the calculation of the dose distributions within the generally irregularly shaped irradiation volumes, an iterative algorithm has been formulated following the differential sector addition method and an equivalent TAR scheme. The quality of such a modifier can be checked by standard dosimetric methods. Deviations from the planned dose modification can be defined as sigma = +/- 5% for the radiation qualities employed (60Co gamma radiation and 15 MeV bremsstrahlung of a linear accelerator).

Gamma Rays↗
PubMed1987

[Clinically-oriented hints for the technic of integrated dosage modification in a partial irradiation field].

The authors present a method allowing the application of doses differing from the reference dose in partial zones of an irradiation volume. The compensator-integrated modification is performed by a simultaneous dose harmonization in the reference plane. Three methods are described by which a topographic and anatomic assignment of field and partial field is possible on the basis of the irradiation features. The optimum application of each method in the individual irradiation schemes is discussed.

Humans↗
PubMed1987

[Presentation of a new partial-field blocker for breast-preserving therapy of breast carcinoma].

A combination of conservative surgery and locoregional radiotherapy is a promising conception for conservative treatment of the so-called little mammary carcinoma. As a further increase of the longterm healing rate is probably almost impossible to achieve, changes of the irradiation technique aim at present only to improve the irradiation quality. With this background, the authors have developed a partial field blocker considering the anatomic and topographic radiophysical features of this therapy method and making possible furthermore various individual treatment modalities. The construction, function and clinical importance of this partial field blocker are described in detail and the physical parameters changing with respect to open field irradiation are discussed.

Breast Neoplasms↗
PubMed1986

General and specific aspects of experimental dose measurement in total body irradiation (TBI).

In magna-field irradiation using high energy bremsstrahlung (photons), i.e. total body irradiation, it is desirable to achieve a homogeneous dose distribution or to realize a planned modification in dose deposition within the target volume. In the Department of Radiology, University of Kiel, for this purpose individually constructed compensators are in routine use for about three years. Some physical and dosimetric aspects of this irradiation technique are described briefly and the experimental test procedure for TBI-compensators is highlighted by several details, for example transmission measurements, radiographies of the compensators and determination of actual dose rates in the midplane of the patient.

Humans↗
PubMed1985

Evaluation of adrenal function in psittacine birds, using the ACTH stimulation test.

The effect of ACTH (16 units) on plasma cortisol and corticosterone concentrations in healthy psittacine birds was evaluated. Plasma corticosterone significantly increased (P less than 0.01) from a mean (+/- SD) basal concentration of 3.25 +/ 3.6 ng/ml to 26.47 +/- 9.25 (one hour after ACTH administration) and 25.69 +/- 13.23 ng/ml (2 hours after ACTH administration). For maximal increase in plasma corticosterone as measured by radioimmunoassay (RIA), heat denaturation was necessary to release corticosteroids from steroid-binding proteins. As measured by RIA, plasma cortisol concentrations did not increase, whether or not the heat denaturation step was included. Addition of cortisol to avian plasma did not prevent accurate quantification of cortisol as measured by RIA. Plasma corticosterone concentrations in cockatoos, macaws, Amazon parrots, conures, and lorikeets before and after ACTH administration indicated that the ACTH stimulation test could be used to evaluate adrenal secretory capacity in psittacine birds.

Adrenal Cortex Function Tests↗
PubMed1984

[Presentation of a new shutter and compensator table for radiotherapy].

A shutter and compensator table for radiotherapy is presented which is moved by a motor and adjusted to a fixed position with respect to the irradiation unit. It is equipped with removable rotation plates, each possessing six trays for shutters and compensators. By hydraulic and infinitely variable regulation, these plates can be brought into different distances from the source to the lower edge of the shutter, one of the trays always lying precisely within the vertical axis of the central tray. The application of this equipment allows a very good reproduction of the geometric irradiation parameters and is easily operable in common practice.

Radiotherapy↗