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Biomedical subjects

A Wambersie

Publications and source records attributed to A Wambersie.

At least 127 records · Page 7Linked to original sources
PubMed1984

[Improvement of the microcinematography technic for the study of cell cycles].

An improvement of time-lapse microcinematography technique is described. It consists in directly printing the time on the microscopical frame, at the moment of the shooting. The time (digital watch), as well as other relevant parameters (temperature etc.) are displayed on a "parameter board", the image of which is encrusted into the microscopical frame by means of an auxiliary two-component lens system. These lenses (current type of microscopical and photographical objectives) are centered on an axis perpendicular to the microscope-camera axis and provide a reduced image of the "parameter board", which is projected on the film edge after deflection by a 45 degree mirror. The latter (aluminized perspex sheet) is located above the photographical eyepiece; it is pierced at the place of the eyepoint in order to give way to the light rays coming out of the cellular culture.

Animals↗
PubMed1984

[Relative biological effectiveness of weak doses of neutrons for the production of dicentric chromosomes in human lymphocytes].

The induction of dicentric chromosomes in G0 human lymphocytes has been used to determine the Relative Biological Effectiveness (RBE) of low doses of d(16 MeV)-Be, d(33 MeV)-Be and d(50 MeV)-Be neutrons. Comparison of the dose-response curves obtained for neutrons with that found for gamma-rays indicates that RBE increases with decreasing neutron dose and with decreasing neutron energy, from d(50 Mev)-Be to d(16 MeV)-Be neutrons. The maximum RBE value at low doses has been evaluated by the linear components of the dose-response curves. It is equal to 14.0, 6.2 and 4.7 for the d(16 MeV)-Be, d(33 MeV)-Be and d(50 MeV)-Be neutrons respectively, when compared with the effects produced by the gamma-rays from 60-Co.

Adult↗
PubMed1983

Improvement of a p(65)+Be neutron beam for therapy at Cyclone, Louvain-la-Neuve.

The variable energy cyclotron of the Catholic University of Louvain is used to produce intense neutron beams for neutron therapy purposes. As a first step, neutrons were produced by bombarding a Be target with 50 MeV deuterons; at present they are produced by 65 MeV protons. This paper describes the improvements to the target system. A new (17 mm) Be target together with the old (10 mm) Be target are inserted in a movable support which allows the production of neutrons either by 65 MeV protons or by 50 MeV deuterons. Both targets can be removed for proton beam therapy. The dosimetric characteristics of the p(65)+Be and d(50)+Be neutron beams are compared: dose rate, gamma-contribution, depth dose and room activation.

Fast Neutrons↗
PubMed1983

OER and RBE of high energy neutron beams for growth inhibition in Vicia faba.

The radiobiologic characteristics of 15 MeV neutrons produced by the d + T reaction at the TNO of Rijswijk and of neutrons produced by the d(50) + Be and p(75) + Be reactions at the cyclotron Cyclone of Louvain-la- Neuve were compared. Growth inhibition in Vicia faba bean roots was used as biologic system. An OER value of 1.5 +/- 0.1 ws obtained for the neutron beams compared. The RBE of 15 MeV, d(50) + Be and p(75) + Be neutrons was found equal to 3.4 +/- 0.2, 3.2 +/- 0.2 and 2.9 +/- 0.3, respectively, relative to gamma rays, for a total (n + gamma) absorbed dose of 0.6 Gy.

Fabaceae↗
PubMed1983

The effects of a fractionated gamma irradiation on life shortening and disease incidence in BALB/c mice.

BALB/c male mice (12 weeks old) were exposed to a single or fractionated exposure of 137Cs gamma rays. The fractionated dose was split into 10 equal doses delivered at an interval of 1 day. The causes and possible causes of spontaneous death were ascertained by autopsy and histological examination, and the data were treated by competing risk analysis. Life shortening followed a linear dose dependency and was about the same for fractionated (38.1 +/- 3.1 days/Gy) as for single (46.2 +/- 4.3 days/Gy) exposure. Death from tumor disease was enhanced and that from nonstochastic lung and kidney diseases was reduced after fractionated compared to single exposure.

Animals↗
PubMed1983

Life shortening and disease incidence in BALB/c mice following a single d(50)-Be neutron or gamma exposure.

Male BALB/c mice, 12 weeks old, were given a single exposure of either 137Cs gamma rays or d(50)-Be neutrons at a dose rate of 3 Gy/min. The animals were kept until death, and causes of death or possible causes of death were ascertained by autopsy and histology. The data were evaluated by competing risk methods. The survival time dose-effect curve for both types of exposure was linear and did not differ significantly (slopes: 55.8 +/- 4.0 days/Gy for neutrons and 46.2 +/- 4.3 days/Gy for gamma rays). The incidence of different diseases also was similar for both groups except that more carcinomas, sarcomas, and myeloid leukemias seemed to occur after neutron exposure and that nonstochastic lung and kidney diseases seemed to arise at lower doses.

Animals↗
PubMed1983

Influence of dose rate on fast neutron OER and biological effectiveness determined for growth inhibition in Vicia faba.

The influence of dose rate on the effectiveness of a neutron irradiation was investigated using growth inhibition in Vicia faba bean roots as biological system. d(50) + Be neutron beams produced at the cyclotron CYCLONE of the University of Louvain-la-Neuve were used, at high and low dose rate, by modifying the deuteron beam current. When decreasing the dose rate from 0.14 Gy.min-1 to 0.2 Gy.h-1, the effectiveness of the neutrons decreased down to 0.84 +/- 0.05 (dose ratio, at high and low dose rate. Dhigh/Dlow, producing equal biological effect). Control irradiations, with 60Co gamma-rays, indicated a similar reduction in effectiveness (0.84 +/- 0.03) when decreasing dose rate from 0.6 Gy.min-1 to 0.7 Gy.h-1. In previous experiments, on the same Vicia faba system, higher RBE values were observed for 252Cf neutrons, at low dose rate (RBE = 8.3), compared to different neutron beams actually used in external beam therapy (RBE = 3.2 - 3.6 for d(50) + Be, p(75) + Be and 15 MeV (d, T) neutrons). According to present results, this higher RBE has to be related to the lower energy of the 252Cf neutron spectrum (2 MeV), since the influence of dose rate was shown to be small. As far as OER is concerned, for d(50) + Be neutrons, it decreases from 1.65 +/- 0.12 to 1.59 +/- 0.09 when decreasing dose rate from 0.14 Gy.min-1 to 0.2 Gy.h-1. Control irradiations with 60Co gamma-rays have shown an OER decrease from 2.69 +/- 0.08 to 2.55 +/- 0.11 when decreasing dose rate from 0.6 Gy.min-1 to 0.7 Gy.h-1. These rather small OER reductions are within the statistical fluctuations.

Cobalt Radioisotopes↗
PubMed1982

The European experience in neutron therapy at the end of 1981.

We present here a survey of the European neutron therapy facilities. For head and neck tumors, the excellent results reported from Hammersmith were not confirmed by an EORTC combined trial (Amsterdam, Edinburgh and Essen). For salivary glands, high percentages (75%) of local control were obtained in Hammersmith and in Amsterdam, as well as in other centers. Following the promising results reported from Hammersmith, neutron therapy of soft tissue sarcomas was started in several centers. For patients with no clinical evidence of residual tumor after surgery, a local control rate ranging between 70% and 90% was achieved (Essen, Hamburg, Heidelberg, Louvain-la-Neuve). For patients with "gross" residual tumor, or with inoperable tumors, the percentages of local control vary within large limits (20-75%) from center to center, probably according to differences in histology, tumor localization, tumor size or extention, and perhaps fractionation (Hammersmith, Edinburg, Amsterdam, Essen, Hamburg, Heidelberg, Louvain-la-Neuve). A study on bronchus carcinoma, performed in Heidelberg, did not show any benefit with neutron therapy. Patients with locally extended cervix and prostate carcinoma were treated in Louvain-la-Neuve according to the RTOG protocol; an excellent early tolerance was noticed. However, for both sites, it is too early to derive valid long term conclusions. For prostatic tumors, a complete regression is usually achieved. For bladder carcinoma, the results from Manchester did not indicate a significant difference between neutron and photon therapy, both in initial assessment of results and complications. The Amsterdam group came to similar conclusions.

Bone Neoplasms↗
PubMed1982

Dosimetry of beta sources in radiotherapy I. The beta point source dose function.

The dose distribution around a point source of a beta-emitting radionuclide in an homogeneous medium is considered. The beta point dose function proposed by Loevinger in 1956 is discussed with respect to the most recent experimental and theoretical available data of Cross and Berger. The Loevinger function provides a reasonable evaluation of the dose distribution at distances of clinical interest. A re-evaluation of the parameters can still improve the situation. A slightly modified formula provides a description of the dose distribution around 32P and 90Y point sources, which is in close agreement, at all relevant distances, with the data of Cross and Berger. This formula can be integrated to provide the dose distribution around beta sources of other shapes.

Electrons↗
PubMed1982

Comparison of neutron therapy beams produced by 50 MeV deuterons and 65 MeV protons on beryllium.

Neutron beams produced by bombarding a 10 cm thick beryllium target with 50 MeV deuterons have been used at Louvain-la-Neuve since nearly 4 years for routine therapeutic applications. At the end of 1981 they were replaced by neutron beams produced by 65 MeV protons on beryllium, mainly in order to improve the beam penetration in tissues. However, produced of neutrons from the p leads to Be reaction implies some disadvantages, mainly a lower dose rate and a higher activation level. In order to solve the problem a new target configuration was designed, consisting of a remote handled system which permits the use of 2 different target assemblies. The irradiated target is automatically removed immediately after the irradiation which greatly protects against exposure to the staff. The dosimetric characteristics of the d(50)-Be and p(65)-Be neutrons beams are compared.

Beryllium↗
PubMed1982

[Relative biological effectiveness (RBE) of d(50)-Be neutrons (Louvain-la-Neuve) and p(34)-Be neutrons (Orleans) for early intestinal tolerance in mice].

This paper compares the RBE of a neutron beam produced by 50 MeV deuterons on beryllium [d(50)-Be] at the cyclotron CYCLONE of Louvain-La-Neuve and of a neutron beam produced by 34 MeV protons on beryllium [p(34)-Be] of the Hôpital Régional d'Orléans. Early intestinal tolerance in mice was choosen as biological criterium; it is derived from LD50 determination after single and fractionated abdominal irradiation. For d(50)-Be neutrons, RBE was 1.8 +/- 0.2 (with respect to 60Co gamma-rays) for a single fraction. It increases up to 2.1 +/- 0.2 for an irradiation in 2 fractions (3.5 h interval) and reaches 2.5 +/- 0.3, 2.7 +/- 0.3 and 2.5 +/- 0.3 for irradiations in 10 fractions (7 and 3.5 h interval) and 20 fractions (3.5 h interval) respectively. RBE values observed for p(34)-Be neutrons (with respect to 60Co gamma-rays) are not significantly different. For a single fraction RBE = 1.7 +/- 0.2 and for 2 fractions (3.5 h interval) RBE = 2.0 +2- 0.2.

Animals↗
PubMed1982

[Oxygen enhancement ratio (OER) and therapeutic gain factor (GF) for low-dose irradiation with californium-252].

The potential benefit of the introduction of californium-252 in interstitial and intracavitary therapy is related to the greater efficiency of its neutron emission against anoxic cancer cells. In that respect, the oxygen enhancement ratio (OER) of the 252Cf emission has been determined for a continuous low dose rate irradiation. The biological system is growth inhibition in Vicia faba bean roots. A new Vicia faba "BelB" strain has been used, which better tolerates long periods (up to about 10 hours) of anoxia. In a first series of experiments, for a 252Cf (Dn + gamma) dose rate of 0.11 Gy . h-1, an OER of 1.4 +/- 0.1 was observed (the gamma contribution of D gamma to the total absorbed dose Dn + gamma was 0.35 at the position of the root tips). In a second series of experiments, in somewhat different geometrical conditions with a 252Cf (Dn + gamma) dose rate of 0.13 Gy . h-1, an OER of 1.5 +/- 0.1 was observed (D gamma/Dn + gamma = 0.42). The OER values observed for similar irradiation times, with iridium-192 gamma-rays, were 2.3 +/- 0.2 and 2.6 +/- 0.1 respectively, which leads to therapeutic gain factors (GF) of 1.6 and 1.7 respectively. These GF values are slightly lower than those previously obtained (GF = 1.8) on the same system, with d(50)-Be, p(75)-Be and 15 MeV neutron beams.

Californium↗
PubMed1982

[Relative biological effectiveness (RBE) of low-dose californium-252].

Relative biological effectiveness (RBE) of 252Cf, with respect to 192Ir, has been determined at the low dose rates commonly used in interstitial and intracavitary therapy. The biological criterion was growth reduction in Vicia faba bean roots. Two varieties of Vicia faba were used. For Vicia faba Sutton's seeds, an RBE of 5.7 to 6.6 was obtained for 252Cf Dn + gamma doses of 0.5 to 0.2 Gy respectively and at a Dn + gamma dose rate of 0.11 Gy-1. The gamma contribution D gamma/Dn + gamma at the level of the root tipes was 0.35 and the derived RBE of the neutron emission of 252Cf was then 8.2 to 9.7. For Vicia faba Be1B and in the same irradiation conditions, an RBE of 5.1 to 6.2 was obtained for the total (n + gamma) 252Cf emission and for Dn + gamma doses of 0.4 to 0.2 Gy respectively. These values lead to an RBE of 7.4 to 9.0 for the neutron emission of 252Cf. For Vicia faba BelB, but for another source arrangement (Dn + gamma dose rate of 0.13 Gy . h-1 for 252Cf), an RBE of 5.6 to 7.5 was obtained for the total (n + gamma) emission of 252Cf and for Dn + gamma doses of 0.4 to 0.1 Gy respectively. The gamma contribution (D gamma/Dn + gamma) at the level of the root tips was 0.42, and the derived RBE of the neutron emission of 252Cf was then 8.9-12.3.

Californium↗