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Biomedical subjects

A Wambersie

Publications and source records attributed to A Wambersie.

At least 109 records · Page 6Linked to original sources
PubMed1987

Which RBE for iodine 125 in clinical applications?

The problem of the selection of a RBE value for 125I is discussed for clinical applications in interstitial therapy. Microdosimetric studies indicate that the emission of the 125I has a y spectra similar to X-rays of 12-140 keV (conventional X-rays), but differs from 60Co, 137Cs gamma-rays and high energy X-rays. The radiobiological data available show RBE values ranging from 1 to 2.4 for 125I (reference beam 60Co). Although obtained with different biological systems and endpoints, RBE values of 1.15-1.20 are in general observed for high doses and high dose rates. On the other hand, higher RBE values (up to 2) are observed at low doses or low dose rates, which is consistent with theoretical and microdosimetric data.

Humans↗
PubMed1987

What degree of accuracy is required and can be achieved in photon and neutron therapy?

In this paper an attempt is made to formulate criteria for the accuracy in the delivery of absorbed dose to a patient during photon or neutron therapy. These requirements are mainly based on the relative steepness of dose-effect curves for local tumour control and normal tissue damage. A review of these dose-effect curves after photon irradiation shows a great variety in steepness; the curves for normal tissue complications in general may be steeper than those for local tumour control. From these data a standard requirement for the combined uncertainty of type A (random) and type B (systematic), given as one relative standard deviation, in the absorbed dose delivery of 3.5% is proposed, even though it is known that in many cases larger values are acceptable and in a few special cases an even smaller value should be aimed at. From the available radiobiological and clinical data it can be concluded that no statistically significant difference can be observed in the relative steepness of dose-effect curves after photon or neutron irradiation. Similar limits will thus be requested in neutron therapy. The uncertainties in the various steps involved in the delivery of an absorbed dose to a point in a patient have been analysed for a treatment with two parallel-opposed beams. The results of this analysis showed that even for these simple treatment conditions, the required accuracy in the delivery of the absorbed dose cannot completely be obtained in photon therapy, and not nearly in neutron therapy. The uncertainties in physical, radiobiological and clinical approaches for weighting of the biological effectiveness of neutron radiation have been compared. The uncertainty in the RBE ratio will replace the type B uncertainty in the absorbed dose during patient treatment if the same dosimetry protocol is applied during biological and clinical procedures.

Cell Survival↗
PubMed1987

[Relative biological effectiveness (RBE) of neutrons produced by 50 MeV deuterons and by 34, 45, 65 and 75 MeV protons].

RBE of p(34) + Be, p(45) + Be, p(65), + Be, p(75) + Be and d(50) + Be neutron beams produced at the cyclotron "Cyclone" of Louvain-la-Neuve were measured. The biological criterion was the regeneration of the crypts of the intestinal mucosa (50 regenerated crypts per circumference) after abdominal irradiation in mice. Taking the p(65) + Be neutrons as reference, RBE values were found equal to 1.12, 1.07, 1.00 (Ref.), 0.96 and 1.02 respectively. These results are consistent with those published for cell lethality in vitro. However, the RBE variation is smaller than this previously obtained in the laboratory for growth inhibition in Vicia faba.

Activation Analysis↗
PubMed1987

Chromosome aberrations in patients irradiated for pelvic tumours.

Peripheral blood lymphocytes of patients undergoing radiation therapy for pelvic tumours have been examined for the presence of dicentric and centric ring chromosomes. Blood samples were taken, by venipuncture, prior to the first radiotherapy session and 24 h after radiotherapy sessions to allow the mixing of the irradiated lymphocytes in the circulating blood. The yield of dicentrics and centric rings was best fitted by a straight line which, according the maximum likelihood method, corresponds to Y = 1.77 +/- 0.0003 10(-2) D. On this basis the dose inducing ten dicentrics or rings is 5.62 Gy at the target volume and, thus, is intermediate between the doses at the target volumes displaying the same effects in patients treated for mammary carcinoma (15 Gy) or for ankylosing spondylitis (2 Gy).

Adenocarcinoma↗
PubMed1986

[Early cell repair of the lung and the intestine in mice, after irradiation by fast neutrons and gamma rays].

Lung tolerance is assessed from LD50 at 180 days after thoracic irradiation, in mice, with d(50) + Be neutrons and 60Co gamma rays. Early intestinal tolerance is assessed from LD50 at 7 days after abdominal irradiation. Additional dose (Dr) to reach LD50 when a single dose Ds is split into 2 equal fractions Di separated by different time intervals "i", is determined (Dr = 2Di - Ds), Dr is larger after gamma than after neutron irradiation, for lung and intestine. After thoracic irradiation with gamma rays, Dr reaches 3.36, 4.38, 5.12 and 5.37 Gy for "i" = 2, 6, 12 and 24 hours respectively; after neutron irradiation, Dr reaches 0.66, 0.9, 1.29, 1.95 and 1.50 Gy for "i" = 1, 2, 4, 12 and 24 hours. Dr is smaller for intestine; after abdominal irradiation with gamma rays, it reaches 1.99, 2.59, 2.74, 3.11, 3.34, 4.44 and 4.56 Gy for "i" = 1, 2, 3.5, 8, 12, 18 and 24 hours; after neutron irradiation, it reaches 0.13, 0.45, 0.42 and 1.33 Gy for "i" = 1.5, 3.5, 5.5 and 24 hours. After gamma irradiation, early repair is complete after 3.5 hours for intestine and needs 12 hours for lung.

Abdomen↗
PubMed1986

Prospects for the application of fast neutrons in cancer therapy. Radiobiological bases and survey of the clinical data.

The rationale for introducing fast neutrons in therapy initially was a reduction in the Oxygen Enhancement Ratio (OER). The recent radiobiological developments indicate that, more generally, fast neutrons tend to reduce the difference in radiosensitivity between cell lines, or related to the degree of oxygenation (Oxygen Gain Factor), the position of the cells in the mitotic cycle (Kinetics Gain Factor), etc. The reduction of the differences in radiosensitivity brings a benefit for certain types of tumours (normally resistant to photons), but a disadvantage for other types of tumours (those which can currently be controlled by photon treatment). A review of the available clinical data is presented. The tumour types or sites for which a benefit has been observed are discussed: locally advanced tumours of the salivary glands, paranasal sinuses, some tumours of the head and neck area with metastatic lymph nodes, slowly growing, well differentiated soft tissue sarcomas, inoperable/recurrent melanomas, locally extended (C, D1) prostatic adenocarcinomas. Selection of the patients suitable for neutron therapy remains the main problem. Collaboration between neutron therapy centres is essential to accelerate the acquisition of sufficient clinical data needed in order to improve patient selection, as well as the optimum modality of application of fast neutrons.

Energy Transfer↗
PubMed1986

Current results of neutron therapy at the UCL, for soft tissue sarcomas and prostatic adenocarcinomas. Université Catholique de Louvain.

From March 1978 to August 1985, 630 patients were treated with fast neutrons at the UCL cyclotron of Louvain-la-Neuve. Neutrons are produced by bombarding a beryllium target with 65 MeV protons. A CNPF of 2.8 was adopted. As far as soft tissue sarcomas are concerned, 32 patients were irradiated after "radical" surgery: only 2 local recurrences were observed (follow-up from 6 months to more that 5 years). On the other hand, in a group of 26 patients with large inoperable, recurrent of incompletely resected tumours, local control could not be achieved in 14 cases. In the whole group of these 58 patients, 12 severe complications were observed; their frequency increases with field size which in turn reflects tumour extent. Locally extended prostatic adenocarcinomas (stage C) were treated with mixed schedule irradiation (3 neutron and 2 photon fractions per week). A local control rate of 93% at 1 year, of 83% at 2 years, and 90% at 3 years was achieved (28, 23 and 10 patients respectively). The early and late tolerance was excellent; only one complication was observed.

Adenocarcinoma↗
PubMed1985

A neutron-photon treatment planning intercomparison.

In order to assess different treatment philosophies in different neutron therapy centres as well as to gauge the quality of neutron dose distributions relative to corresponding photon plans, a neutron-photon treatment planning intercomparison has been organized amongst the neutron therapy centres in Europe and the U.S.A. Treatment plans were compared for patients with a tumour in the floor of the mouth, a carcinoma of the base of the tongue and a large bladder carcinoma. A wide variety in treatment plans was received. This was mainly caused by the different assumptions on the treatment margin around the tumour and whether or not the lymph nodes should be irradiated electively. Within the same institute, however, similar types of plans were used for both the neutron and the photon irradiations. The homogeneity of the adsorbed dose over the target volume can be made almost the same for photon and neutron irradiations, although this may require a more complicated technique for neutron treatment. The relative absorbed dose to normal tissues was somewhat higher for the neutron treatment. There is an increased chance of the occurrence of a hot spot with the relatively low energy neutron beams compared to the photon beams.

Aged↗
PubMed1985

[Determination of parameters of the survival curve of the stem cells of the intestinal crypts by LD50 and the regenerated crypt count. Determination of the RBE of p(65) + Be neutrons].

The early effects of an irradiation on the intestinal epithelium have been evaluated, at the tissular level, by LD50 after single and multifraction irradiation, and, at the cellular level, by numeration of the regenerated intestinal crypts (Withers technique) after a single fraction irradiation. From the set of informations provided by both criteria, one derived the values of the parameters defining the survival curve of the intestinal clonogenic crypt cells after irradiation by gamma-rays (two component model): D0 = 1.5 Gy, 1D0 = 4.5 Gy, nD0 = 2.25 Gy and n = 20. In other respects, the p(65) + Be neutrons RBE (ref. 60-Cobalt) after a single fraction irradiation is equal to 1.75 +/- 0.2 and 1.64 +/- 0.25 for the LD50 at the 5th day and for the regeneration of 50 crypts after 3.5 days respectively.

Animals↗
PubMed1985

[Comparative kinetics of the early repair of intestines and lung in mice after fast neutron and gamma-ray irradiation].

Early repair (Elkind) after d(50) + Be neutron and gamma irradiation is assessed by determining the additional dose Dr necessary to reach a given biological effect when a single fraction Ds is split into 2 equal fractions 2Di separated by a time interval "i". LD50 at 180 days after thoracic irradiation is used as an evaluation of late pulmonary tolerance; LD50 at 5 days after abdominal irradiation is used as an evaluation of early intestinal tolerance. Dr is reduced but still important after neutron irradiation as compared to gamma irradiation. For LD50/180, after fast neutron irradiation Dr reaches 66, 90, 64, 162, 195, 150 cGy for "i" = 1, 2, 3, 5, 4, 12, and 24 hours respectively; after gamma irradiation, Field and Hornsey reported Dr = 390, 530, and 376 cGy for "i" = 2, 6, and 24 hours respectively; after neutron irradiation, they reported Dr = 190 cGy for "i" = 24 hours. For LD50/5, after fast neutron irradiation, Dr = 14, 45, 43, and 133 cGy for "i" = 1,5, 3,5, 5,5 and 24 hours respectively. Early repair is faster after gamma irradiation: Dr reaches a maximum for "i" = 3-4 hours. For neutrons, Dr reaches its maximum at 24 hours for both criteria.

Animals↗
PubMed1985

[Microcinematographic study of the lengthening of the cell cycle after x-ray and fast neutron irradiation].

The median cycle duration of unirradiated EMT6 cells is equal to 9.68 +/- 0.20 h. It reaches 10.77 +/- 0.42 h, 12.95 +/- 0.62 h, 14.95 +/- 1.10 h, 16.15 +/- 1.87 h and 20.25 +/- 2.25 h after 250 kV X-rays doses of 1 Gy, 2 Gy, 4 Gy, 6 Gy and 8 Gy respectively and 11.23 +/- 1.03 h, 13.40 +/- 0.53 h and 15.13 +/- 1.15 h after p(65) + Be neutron doses of 0.75 Gy, 1.5 Gy and 2.5 Gy respectively. The corresponding mitotic delay (Tc irradiated - Tc controls) may be evaluated equal to congruent to 1.15 h per Gy for X-rays and to congruent to 2.30 h per Gy for neutrons.

Animals↗
PubMed1985

Review and evolution of clinical results in the EORTC Heavy-Particle Therapy Group.

Part of the clinical results from the "EORTC Heavy-Particle Therapy Group" are reviewed (September 1984). Fast neutrons can bring a significant benefit, compared to conventional photon (or electron) techniques, in well defined patient series. A benefit for neutrons is observed, in Hammersmith and in Amsterdam, for locally extended salivary gland tumours. Soft tissue sarcomas can also be considered as a good indication for neutron therapy, especially when they are slowly growing and well differentiated, as shown in Essen, Hammersmith and Louvain-la-Neuve. Neutrons can bring an advantage in the treatment of some melanoma patients as shown in Hammersmith. For locally advanced prostatic carcinoma, better results for neutrons are shown in Hamburg and Louvain-la-Neuve. These data are similar to those observed in the United States from the RTOG studies. Due to a reduced differential effect between tissues after neutron treatment, irradiation of large volumes of normal tissues, at high neutron dose, should be avoided. Different possible combinations between neutrons and photons (boost, mixed schedule) are discussed.

Adenocarcinoma↗
PubMed1985

Induction of chromosome aberrations in G0 human lymphocytes by low doses of ionizing radiations of different quality.

Human peripheral blood lymphocytes from two donors were exposed to low doses (0.05 to 2.0 Gy) of gamma rays, X rays, or fast neutrons of different energies. Chromosome aberrations were analyzed in metaphase of first-division cells after a culture time of 45-46 hr. At this time, less than 5% of the cells were found in second division. Different dose-response relationships were fitted to the data by using a maximum likelihood method; best fits for radiation-induced dicentric aberrations were obtained with the linear-quadratic law for all radiations. The linear component of this equation predominated, however, for neutrons in the range of doses studied, and the frequency of dicentrics induced by d(16)+Be neutrons up to 1.0 Gy could also be described by a linear relationship. The relative biological efficiency (RBE) of X rays and d(16)+Be, d(33)+Be, and d(50)+Be neutrons compared to 60Co gamma rays in the low dose range was calculated from the dose-effect relationships for the dicentrics produced. The RBE increased with decreasing neutron dose and with decreasing neutron energy from d(50)+Be to d(16)-+Be neutrons. The limiting RBE at low doses (RBEo) was calculated to be about 1.5 for X rays and 14.0, 6.2, and 4.7 for the d(16)+Be, d(33)+Be, and d(50)+Be neutrons, respectively.

Beryllium↗
PubMed1985

Results of neutron therapy of locally advanced soft tissue sarcomas at Louvain-la-Neuve.

Between March 1978 and October 1983, 65 patients with locally advanced soft tissue sarcomas were treated at the cyclotron of Louvain-la-Neuve. 46 patients are analysed, 19 patients with intraabdominal or intrathoracic lesions are excluded. After "radical surgery" (no "gross tumour" present at the time of neutron therapy), a local control rate of 93% was achieved (25/27 patients) and the survival was 74%. In a second group of 19 patients with incompletely resected, or recurrent, or inoperable tumour, a local control was obtained in four cases (21%), and 13 patients were alive (69%). The follow-up ranged from three to 65 months (mean: 25,9 months). Ten severe complications were observed (22%); they were related to the field sizes, which reflected the local tumour extent.

Belgium↗
PubMed1984

The role of the ICRU in quality assurance in radiation therapy.

A short history of the International Commission on Radiation Units and Measurements (ICRU) and its main objectives are presented. They now include the development of internationally acceptable recommendations regarding: (1) quantities and units; (2) procedures suitable for the measurement and application of these quantities (as well as the associated uncertainties); (3) physical data needed in the application of these procedures; and (4) definition of terms and concepts used in radiation therapy. One of the most important actions of the ICRU during the last two decades was its recommendation in favor of the introduction of the SI units (International System of Units) in the field of ionizing radiation. In addition, in order to facilitate its use, the ICRU recommended the adoption of new special names in the SI system: gray, becquerel and sievert. Recently published ICRU reports in the field of radiation therapy are reviewed. Reports 23 and 24 provide recommendations for determining the absorbed dose in a patient irradiated with X or gamma ray beams. High energy electron and neutron beams have been considered in Reports 21 and 26 respectively. Report 31 provides a survey of the available W values and Report 29 makes recommendations on dose specification for reporting therapeutic irradiation in external beam therapy. A report dealing specifically with Quality Assurance in radiation therapy is in preparation.

Humans↗