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Biomedical subjects

A Wambersie

Publications and source records attributed to A Wambersie.

At least 91 records · Page 5Linked to original sources
PubMed1989

Results of 10 y of radiation protection dosimetry at the neutrontherapy facility in Louvain-la-Neuve.

After 10 y of routine operation, radiation hazards to the neutron therapy staff at Louvain-la-Neuve were evaluated. These hazards to the staff in neutron therapy are a matter of concern, not only because of the dose levels due to induced activation after treatment but also because of the difficulty of evaluating adequately the dose equivalent rates (including the quality factor, QF) during the irradiation. Build-up of radioactivity near the collimator and in the therapy room is reported. In the beam axis, dose rates due to activation can amount up to 5 mGy h-1. However, these rates are efficiently reduced to 0.3 mGy h-1 by automatically withdrawing the target after irradiation. Other problems of radioactive contamination (for instance, the choice of the Fe composition of the collimator) are discussed. Dose equivalent rates were determined during treatment at different positions inside and outside the treatment room. At these locations, neutrons of widely varying energies are present, accompanied by a significant proportion of gamma rays. The measurements of neutron-dose equivalent rates were performed with three commercial neutron detectors: a BF3 and a He3 remcounter (Nuclear Enterprises and Nardeux) and the Dineutron multisphere remcounter (Nardeux). The Dineutron also allowed the evaluation of QF. The results of these detectors were compared with the results of the integration of microdosimetry spectra obtained in free air with a TE proportional counter (Far West Technology). For the p(65) + Be neutrons, the dose equivalent rate was equal to 0.4 Sv h-1 in the treatment room (at 2.5 m from the collimator) and was reduced to 2-3 microSv h-1 at the room entrance. The gamma component increased from 55% to 95% at the same positions, respectively. Ratios of the responses of all detectors and QF values are compared and discussed at the different positions. The whole-body dose equivalents to the neutron therapy staff over the 10 y considered are presented; although they are higher than for conventional radiotherapy, they remain far below the ICRP recommended dose limits.

Fast Neutrons↗
PubMed1989

Kinetics of sublethal damage recovery in mouse lip mucosa comparing low and high-LET radiation.

The effects of d(50) + Be neutrons on the lip mucosa in mice were investigated as a model of early effects. The biological endpoint eas the incidence of desquamation in the lower lip after selective irradiation of the snout of the animals. ED 50 (dose leading to desquamation in 50% of the animals) were calculated by probit analysis. Fractionated (two, four and ten fractions) and protracted (43.5, 11.5 and 0.88 Gy.h-1) irradiations have been carried out. Results were analysed using the mathematical method of Dale. An alpha/beta of 39.6 Gy and a t 1/2 of recovery of sublethal damage of 47 min have been derived. These results have been compared to data previously obtained with cobalt-60 gamma rays. Using the same mathematical approach, and comparing similar fractionated and protracted experiments, an alpha/beta of 7.4 Gy and a t 1/2 of recovery of 47 min have been calculated. There was no significant difference in the repair kinetics after irradiations with gamma rays or d(50) + Be neutrons.

Animals↗
PubMed1989

Is there any future for high-LET radiation?

In order to judge the possible future of high-LET radiotherapy several physical, biological and clinical aspects are reviewed and discussed. This concerns firstly ongoing improvements of physical selectivity for low-LET radiation. One new approach in this respect are high energy particle beams such as protons or helium ions. Their clinical benefit has been demonstrated for several well selected tumour types or sites (e.g. uveal melanomas). Secondly the specific radiobiological properties of high-LET radiation are reviewed. The rationale for introducing neutron radiotherapy historically was a reduction in OER. However, there is now evidence that all cell populations, in all conditions, tend to respond in a more similar way when exposed to neutrons compared to photons. A reduction in the differences in radiosensitivity can bring an advantage or a disadvantage depending on the tumor characteristics and on the normal tissue at risk. This raises the important problem of patient selection for neutron therapy. High LET radiations were proved to be superior to low-LET radiations for the treatment of some tumour types such as salivary gland tumours, locally extended prostatic adenocarcinoma, or some types of sarcomas. Development of heavy ion therapy programs is justified for some types of tumours requiring the application of high-LET radiations with a high physical selectivity. Finally the clinical consequences of new technological developments for low and high-LET radiations are discussed.

Dose-Response Relationship, Radiation↗
PubMed1989

Radiobiological intercomparisons of fast neutron beams used in therapy.

A research program was performed at Louvain-la-Neuve to systematically determine the RBE of fast neutrons for the growth inhibition in Vicia faba bean roots and for the regeneration of the intestinal crypts in mice. The following neutron beams were compared p(75) + Be, p(65) + Be, p(45) + Be, p(34) + Be, d(20) + Be, and d(50) + Be. The RBE-variation as a function of neutron energy is larger for the Vicia faba system than for the regeneration of the intestinal crypt cells. This can be related to the inherent differency of the biological systems, but also to the different dose ranges involved (0.33 to 0.56 Gy and 7.66 to 8.56 Gy, respectively). In the high energy range explored, defined by the reactions p(75) + Be to p(34) + Be RBE varies only between 0.92 and 1.28 for Vicia faba and 0.96 and 1.12 for crypt cells normalized to the p(65) + Be beam. By contrast the RBE at lower energy beams (d(20) + Be and d(14.5) + Be) reaches values between 1.5 and 1.6 Finally fractionation has shown to be likely more important at the high energy beams.

Animals↗
PubMed1989

Early repair kinetics of intestine and lung in mice, after fast neutron and photon irradiation.

Early repair (Elkind repair) kinetics of an early and a late responding tissue after gamma and d(50) + Be neutron irradiation were compared in mice. LD50 at five days after abdominal irradiation and LD50 at 180 days after thoracic irradiation were chosen as biological endpoints to study intestinal and lung tolerance, respectively. Elkind repair is assessed from the additional dose Dr to reach LD50 when a single dose Ds is split into two equal fractions Di separated by time intervals "i" ranging from 0 to 24 hours (Dr = 2Di-Ds). Dr is greater for lung than for intestine after both gamma and neutron irradiations. Our data are consistent with an exponential early repair with an half-life (T 1/2) of 0.5 h for intestine and 1.5 to 2 h for lung.

Animals↗
PubMed1989

Neutron therapy of soft tissue sarcoma at Louvain-la-Neuve (interim results 1987).

The results of fast neutron therapy of soft tissue sarcoma at the cyclotron of Louvain-la-Neuve are reviewed. 75 patients were analysed, the follow-up ranged from six to 102 months (mean: 30.7 months). 47 patients were treated after radical surgery. A local control rate of 91.5% (43/47) was achieved, and 70% of the patients are alive. 28 patients were irradiated with gross tumour present at the time of neutron therapy (recurrence, incomplete resection, inoperable): a local control was achieved in 5/28 cases (18%), and 68% of the patients are alive. A complication rate of 16% was recorded which was directly related to the treatment volume.

Combined Modality Therapy↗
PubMed1989

Radiobiological intercomparison of clinical neutron beams for growth inhibition in Vicia faba bean roots.

Relative biological effectiveness (RBE) and oxygen enhancement ratio (OER) values of different neutron beams produced at the variable energy cyclotron "Cyclone" of Louvain-la-Neuve (Belgium) were determined. The neutrons were obtained by bombarding a beryllium target with 34-, 45-, 65-, or 75-MeV protons or with 50-MeV deuterons. The biological system was growth inhibition in Vicia faba bean roots. Taking the p(65) + Be neutron beam as a reference, RBE values were found equal to 1.36 +/- 0.2, 1.20 +/- 0.1, 1.00 (ref), 0.98 +/- 0.1, and 1.18 +/- 0.1, respectively; the doses corresponding to 50% growth inhibition were 0.39, 0.44, 0.53, 0.54, and 0.45 Gy. For the same beams, OER values were found equal to 1.55 +/- 0.1, 1.38 +/- 0.1, 1.29 +/- 0.1, 1.41 +/- 0.1, and 1.60 +/- 0.2, respectively.

Growth↗
PubMed1988

Neutron therapy in cervical cancer: results of a phase III RTOG Study.

Between October 1976 and May 1984, 156 patients with locally advanced cervical cancer were entered into a Phase III trial with the participation of five institutions. Patients were randomly assigned to receive photons only (50 Gy in 25 fractions over 5 weeks plus intracavitary applications or external-beam boost) or mixed-beam radiotherapy (2 fractions a week of neutrons, 3 fractions a week of photons to a total RBE-adjusted dose of 50 Gy over 5 weeks plus intracavitary applications or external mixed-beam boost). Only patients with squamous carcinoma of FIGO Stages IIB, III, or IVA with negative para-aortic nodes on lymphangiogram were eligible. Ten patients were excluded from the analysis because of ineligibility or cancellation. Of the 146 patients analyzed, 80 were treated with mixed-beam radiotherapy and 66 with photons. Patients were grouped by stage and institution. The percentage of patients undergoing intracavitary applications was 50% on mixed beam and 75% on photons (p less than 0.01). Tumor clearance was 52% and 72% for mixed beam and photons, respectively (p less than 0.03). Local control at 2 years was 45% for mixed beam and 52% for photons. Median survivals were 1.9 years on mixed beam and 2.3 years on photons. Severe complications occurred in 19% and 11% in mixed beam and photons respectively (p less than 0.13). The inferior outcome with neutron therapy in this study may have resulted from the use of horizontal neutron beams of varying energy and penetration. A new randomized trial using high-energy hospital-based cyclotrons with gantry-mounted beam-delivery systems has recently been activated to evaluate more rigorously the role of fast-neutron therapy for advanced cervical cancer.

Adult↗
PubMed1988

Bone vitality in the cat's irradiated jaw. Histological study.

The vitality of the mandible in cats was studied from two to 15 months after irradiation. Dose of 80 Gy in three days was delivered using three hairpin shape iridium-192 wires surrounding the mandibula. The osseous vitality was assessed from the percentages of lacunae inhabited by osteocytes (IL). The results are compared with those obtained by microradiography. At two months, a small reduction of vitality is already observed, it becomes progressively more important. At one year, vitality is recovered nearly fully in the ventral part of the mandibula, mainly at the level of the alveolar crest. Vitality remains reduced in the dorsal part. Microradiographic lesions appear more slowly; they are apparent at six months.

Animals↗
PubMed1988

Life-shortening and disease incidence in C57Bl mice after single and fractionated gamma and high-energy neutron exposure.

C57Bl Cnb mice were exposed to single or fractionated d(50)+Be neutrons or 137Cs gamma-ray exposure at 12 weeks of age and were followed for life-shortening and disease incidence. The data were analyzed by the Kaplan-Meier procedure using as criteria cause of death and possible cause of death. Individual groups were compared by a modified Wilcoxon test according to Hoel and Walburg, and entire sets of different doses from one radiation schedule were evaluated by the procedure of Peto and by the Cox proportional hazard model. No significant difference was found in life-shortening of C57Bl mice between a single gamma and neutron exposure. Gamma fractionation was clearly less effective in reducing survival time than a single exposure. On the contrary, fractionation of neutrons was slightly although not significantly more effective in reducing life span than a single exposure. Life-shortening appeared to be a linear function of dose in all groups studied. The data on causes of death show that malignant tumors, particularly leukemias including thymic lymphoma, and noncancerous late degenerative changes in lung were the principal cause of life-shortening after a high single gamma exposure. Exposure delivered in 8 fractions 3 h apart was more effective in causing leukemias and all carcinomas and sarcomas than one delivered in 10 fractions 24 h apart or in a single session. Following a single neutron exposure, leukemias and all carcinomas and sarcomas appeared to increase somewhat more rapidly with dose than after gamma irradiation. No significant difference in the incidence of leukemias and all carcinomas and sarcomas was noted between a single and a fractionated neutron exposure.

Animals↗