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Biomedical subjects

A Wambersie

Publications and source records attributed to A Wambersie.

At least 19 recordsLinked to original sources
PubMed1992

Variation of RBE between p(75) + Be and d(50) + Be neutrons determined for chromosome aberrations in Allium cepa.

The RBE of p(75) + Be neutrons relative to d(50) + Be neutrons has been determined for chromosome aberrations induced in Allium cepa (onion) roots. Two biological criteria were selected: the average number of aberrations (mainly fragments) per cell in anaphase and telophase, and the percentage of aberration-free cells. The influence of sampling time (3 to 7 h incubation) between irradiation and fixation was investigated systematically. This factor did not significantly influence the results. The RBE values of p(75) + Be neutrons compared to those of d(50) + Be neutrons were 0.85 (0.79-0.91) and 0.87 (0.80-0.95) for the first and the second criteria, respectively. In previous experiments for the same beams, we found an RBE of 0.90 (0.86-0.94) for survival of V79 cells (D0 ratio), 0.96 (0.93-0.99) for the intestinal crypt cell system, and 0.83 (0.70-0.96) for Vicia faba growth delay.

Allium↗
PubMed1991

Application of the LQ model to the interpretation of absorbed dose distribution in the daily practice of radiotherapy.

In 1991, the vast majority of radiotherapy centers are implemented with computer treatment planning systems (TPS), and it has become routine practice to compute full absorbed dose distribution (ADD) in almost all treatment situations. Usually the target is covered by the 100% isodose and the surrounding normal tissues receive a lesser dose than the tumor. It implies, that, as the dose per fraction of, say, 2 Gy is prescribed at the 100%, normal tissues receive a daily dose different than 2 Gy. The absorbed doses delivered at different organs have therefore not the same biological effectiveness and must be corrected according to the actual dose per fraction for a proper interpretation of the treatment planning. This is of great importance since most of the "tolerance levels" used in the practice have been determined for doses per fraction around 1.8-2 Gy. The linear-quadratic (LQ) model provides a simple method for establishing biological equivalencies and has been used throughout this article to establish the difference between the absorbed dose computed by the TPS and its biological equivalent. It is shown that normal tissues receiving less than 100% of the daily dose are relatively more protected than suggested by the ADD, and, inversely, that normal structures overdosed and thus receiving more than the 100% daily dose are relatively more at risk for complications than suggested from the ADD.

Bronchial Neoplasms↗
PubMed1991

A phase I-II trial of induction chemotherapy with carboplatin and fluorouracil in locally advanced head and neck squamous cell carcinoma: a report from the UCL-Oncology Group, Belgium.

Eighty-three patients (median age, 56 years and Karnofsky performance status greater than or equal to 70) were treated with carboplatin (Carbo) and fluorouracil (5Fu) for stage III and IV head and neck squamous cell carcinoma (HNSCC). 5Fu (1 g/m2/d) was administered from day 1 to 4 by continuous infusion. Carbo was given on day 1 and, in order to evaluate its maximum-tolerated dose (MTD), the dose level was progressively increased from 250 mg/m2 to 450 mg/m2. The effectiveness of this association and its potential role in local control were also evaluated. Three patients received Carbo at a dose of 250 mg/m2, 13 received 300 mg/m2, one received 330 mg/m2, 12 received 350 mg/m2, six received 375 mg/m2, 26 received 400 mg/m2, 18 received 420 mg/m2, and four received 450 mg/m2. Two (13 of 83) or three courses (64 of 83), repeated every 4 weeks, were administered. The overall (primary tumor and node) response and complete response (CR) rates were 33% and 14%, respectively. For primary tumor, the response rate (RR) was 57% with 32% CR and 18% pathologic complete response (PCR); the RR was higher for patients with oropharyngeal tumor (76%, P = .037) and for patients treated with Carbo greater than or equal to 350 mg/m2 (65%, P = .02); the tumor size (T1 + T2 v T3 + T4) was a good prognostic factor for RR (90% v 46%, P = .001), CR (65% v 20%, P less than .001), and PCR (45% v 8%, P less than .001). For nodes, the RR was 33% with 11% CR. Grade 3-4 neutropenia and thrombocytopenia were experienced by 17% and 28% of the patients treated with 420 mg/m2 of Carbo and by 50% of the patients treated with 450 mg/m2. The MTD can be fixed at 420 mg/m2 and the proposed dose at 400 mg/m2. Thirty-eight patients were treated with surgery plus radiotherapy, 33 with radiotherapy alone, and seven with surgery alone. The median follow-up is 12 months. The 18-month disease-free survival (DFS) is 78% for overall complete responders and 39% for the others (P = .04). There is no primary tumor recurrence among the 12 patients with a primary tumor PCR treated by radiotherapy alone for tumor control (median follow-up, 17.3 months). The association of Carbo-5Fu is a safe induction chemotherapy regimen for HNSCC. The proposed dose of Carbo for future treatment is 400 mg/m2.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1991

[Prevention of caries and of osteoradionecrosis in patients irradiated in oncology].

Dental lesions following radiation therapy of the head and neck cancers are known for a long time, and the role of a decreased salivary function in the induction of radiation caries has been recognized by Del Regato in 1939. The salivary glands are most frequently included in the radiation fields for the treatment of lesions of the upper aero-digestive tract; they are also irradiated, in variable proportion, in other conditions such as Hodgkin's disease. From a clinical point of view, the dental caries observed after radiation therapy are diffuse and rapidly evolutive. However, from a histological point of view, they are similar to the current type of dental caries. Daily application of fluoride has been shown to prevent the appearance of the caries and of the related osteo-radionecrosis. The experience of the Cancer Centre Georges-François Leclerc of Dijon is reported and especially the results of randomized prospective studies concerning the efficiency of the fluoride prevention. Taking into account the available clinical experience, it seems reasonable, at present, to state that preservation of teeth, in irradiated patients should be the rule and not the exception, given good dental conditions prior to the treatment and patient collaboration. The 5 minutes daily application of fluoride gel is the most reliable method for prevention of post-irradiation dental caries. The twice daily use of high-content fluoride tooth-paste is a good alternative, provided its limitations are well understood by the clinician and the patient. The systematic use of high-content fluoride tooth-paste for the prevention of caries in the general public is discussed.

Dental Caries↗
PubMed1991

[Radiology and radioprotection in dental medicine. 2: Regulations and practical recommendations].

The three general principles of the International Commission on Radiological Protection (ICRP) are first recalled: (1) justification, (2) ALARA, (3) the dose limits. The dose limits to be followed, at present, in Belgium are given for the occupational exposure, the occupational exposure of women (pregnant and not), the exposure of the public. The possible modification of the dose limits by the ICRP is a near future is discussed. The present belgian regulations are reviewed as far as the equipment and the buildings are concerned, as well as for the personal dosimeters and the medical supervision. Finally, the doses delivered to the patients, at different organs, during dental radiological examinations are recalled, e.g. the doses at the skin, the thyroid, the gonads, the eyes, the pituitary gland. The interest of shielding the thyroid and the abdomen is discussed.

Belgium↗
PubMed1991

[Radiology and radiation protection in dental medicine. 1: Biological effects resulting from exposure to ionizing radiation].

The different types of biological effects produced by ionizing radiations are reviewed. Among the early effects following an acute exposure, the bone marrow syndrome and the intestinal syndrome are briefly described. They are unlikely to appear in the current conditions encountered in dental radiology. As far as skin exposure is concerned (e.g. fingers, hands), acute reactions (moist desquamation, ulceration, etc.) require high doses which are encountered only in accidental conditions. However, chronic dermatitis after repeated low dose exposure is one of the major risks in dental radiology (even without previous acute lesions), if the recommendations of radioprotection are not followed. The danger is ultimately the transformation into a radio-induced skin cancer. Among the late effects, after chronic exposure at low doses, cancer induction and the genetic effects are the most important. The risk coefficient for cancer induction is expressed by the number of lethal cancers induced per unit dose. In his last report (1988), the UNSCEAR assessed the risk coefficient between 4.5 and 7% for an absorbed dose of 1 Gy (low-LET radiation, high dose delivered at high dose rate). A low doses and low dose rates (X-and gamma rays), the UNSCEAR recommends to reduce the above risk coefficients by a factor between 2 and 10. The risk coefficient at low doses is difficult to evaluate since the rate of radio-induced cancers is small compared to the spontaneous cancer incidence. The risk of a severe genetic effect is about 1/3-1/4 of the risk of lethality from radio-induced cancer. Finally, the characteristics of the stochastic and non-stochastic effects are described. The acute effects, the late radiodermatitis and the cataract are examples of non-stochastic effects, while cancer induction and the genetic effect are stochastic effects. In the Appendix, the most important quantities and units, used in radiation protection, are presented.

Bone Marrow↗
PubMed1991

Life-shortening and disease incidence in mice after exposure to gamma rays or high-energy neutrons.

Male C57Bl/Cnb and BALB/c mice were exposed to single and fractionated d(50) + Be neutrons or 137Cs gamma rays at 12 weeks of age and were followed for life-shortening and disease incidence as ascertained by autopsy and histological examinations at the time of spontaneous death. Fractionation schedules used were 10 exposures at 24-h intervals and 8 exposures at 3-h intervals for gamma rays, and 8 exposures at 3-h intervals for neutrons. The data were analyzed by the Kaplan-Meier procedure using as criteria causes of death and possible causes of death. Individual groups were compared by a modified Wilcoxon test according to Hoel and Walburg (J. Natl. Cancer Inst. 49, 361-372 (1972)). No significant difference was found in C57Bl/Cnb and BALB/c male mice between a single gamma-ray exposure and a single neutron exposure. Gamma-ray fractionation was clearly less effective in reducing survival time than a single exposure. In contrast, fractionation of neutrons was slightly, although not significantly, more effective in reducing survival time than a single exposure. The relative biological effectiveness (RBE) for life-shortening for d(50)-Be neutrons compared to gamma rays is of the order of 1 to 2 for a single exposure to neutrons and between 2 and 3 for fractionated neutrons compared to a single exposure to gamma rays. Neutron irradiation caused somewhat more cancer than gamma irradiation, and the RBE for cancer induction may be higher, probably between 2 and 3 in the range of 1 to 3 Gy, although the present data do not allow a more precise assessment.

Animals↗
PubMed1990

Review of the clinical results of fast neutron therapy.

The clinical results reported from the different neutron therapy centres are reviewed. Fast neutrons were shown to be useful in the treatment of locally extended inoperable salivary gland tumours (average local control rates 67% for neutrons compared to 28% for photons). For paranasal sinuses and some tumours of the head and neck area, especially extended tumours with large fixed lymph nodes, neutrons could also be of interest. By contrast, the results obtained for brain tumours were, in general, disappointing. Neutrons were shown to be beneficial in the treatment of well differentiated soft tissue sarcomas, as well as to bone- and chondrosarcomas. For locally extended prostatic adenocarcinoma, a RTOG randomized trial gave local control rates of 77% for mixed schedule compared to 31% for photons. Neutrons could be useful also for palliative treatment of melanomas. Further studies are needed in order to evaluate the benefit of fast neutrons for other localizations such as uterine cervix, bladder and rectum. It can be concluded that fast neutrons could be of interest for about 10% of the radiotherapy patients, but it is likely that the new high-energy hospital-based cyclotrons will further extend the indications of neutron therapy. However, patient selection remains one of the main problems and there is a need for development of individual predictive tests.

Brain Neoplasms↗
PubMed1990

Microdosimetric specification of radiation quality in neutron radiation therapy.

The neutron beams used by various radiotherapy centres are of widely differing energies, and differences of up to 50 per cent in the relative biological effectiveness (RBE) between different beams have been found in radiobiological experiments. Moreover, at some facilities RBE variations have been observed with increasing depth in a phantom. In spite of this evidence, there is no quantitative and uniquely accepted specification of radiation quality used in practice. The urgency of an adequate solution of this problem is illustrated by the fact that in radiation therapy the usual accuracy requirement for the quantity of radiation, i.e. the absorbed dose to be delivered to the tumour, is 3.5 per cent (1 SD). In this paper a pragmatic solution for the specification of radiation quality for fast neutron therapy is proposed. It is based on empirical RBE versus lineal energy response or weighting functions. These were established by using existing radiobiological data and microdosimetric spectra measured under identical irradiation conditions at several European neutron irradiation units.

Energy Transfer↗
PubMed1990

Radiobiological intercomparison of two clinical neutron beams using the regeneration of mouse intestinal crypts.

Determination of dose modification factor greatly facilitates the introduction of clinically proven neutron therapy schedules at new installations. We have compared the biological performance of the p(66)+Be neutron facility at Faure, South Africa, with the established p(65)+Be installation at Louvain-la-Neuve, Belgium. Filtration, D gamma/DT, dose rate and HVT 5/15 for the Louvain and Faure beam are: 2 cm, 2.5 cm polyethylene; 3%, 5%; 0.2 Gy/min, 0.4 Gy/min; and 20 cm and 19 cm respectively. Dosimetry was done in A-150 plastic. Irradiation of BALB/C mice was carried on according to the dose accumulation method in a perspex phantom at 5 cm depth and at an SSD of 150 cm at a field size of 28 X 28 cm2. Sections of the jejunum were prepared at each centre and analyzed by both. The RBE of the Faure beam determined at a survival level of 50 crypts ranged from 1.64 to 1.69. The dose modification factor RBE of the Louvain beam given by Beauduin et al. was 1.61 +/- 0.14. The dose modification factor of the Faure beam relative to the Louvain beam is thus 1.03 +/- 0.13 which could be expected from the similarity of the physical characteristics. Independent RBE measurements in a variety of systems also suggest similar biological properties. The depth variation of the RBE was found to be 4% (mouse gut) using 3 cm polyethylene filter over the depth range of 2.5 to 13.5 cm. This is in agreement with microdosimetry measurements using polyethylene filters of various thicknesses and with V79 measurements reported by Slabbert et al.

Animals↗
PubMed1990

Chromosome aberrations induced in vitro in human lymphocytes by monoenergetic 2.5 MeV neutrons and 60Co gamma rays.

The aim of the present experiments was to evaluate the relative biological effectiveness (RBE) of monoenergetic 2.5 MeV neutrons, in view of the scarcity of data on the RBE of neutrons in this energy range. Human peripheral blood lymphocytes from two donors were exposed to doses of neutrons ranging from 0.005 Gy to 0.5 Gy. Gamma rays produced by a telecobalt therapy unit were used as reference radiation. RBE values were of the same order of magnitude, whatever was the model of the dose-response curve chosen for the neutrons (linear or linear-quadratic). As expected, RBE increased markedly with decreasing doses and went beyond 30 at a dose level of 0.2 Gy. The present results, compared with RBE values obtained with neutrons of higher energy (6.5, 14 and 21 MeV), confirm that low energy neutrons are more effective in producing genetic effects, especially at low doses.

Adult↗
PubMed1990

Fast neutron therapy at the end of 1988--a survey of the clinical data.

The clinical results reported from the different neutron therapy centres, in USA, Europe and Asia, are reviewed. Fast neutrons were proven to be superior to photons for locally extended inoperable salivary gland tumours. The reported overall local control rates are 67% and 24% respectively. Paranasal sinuses and some tumours of the head and neck area, especially extended tumours with large fixed lymph nodes, are also indications for neutrons. By contrast, the results obtained for brain tumours were, in general, disappointing. Neutrons were shown to bring a benefit in the treatment of well differentiated slowly growing soft tissue sarcomas. The reported overall local control rates are 53% and 38% after neutron and photon irradiation respectively. Better results were also reported for bone- and chondrosarcomas. The reported local control rates are 54% for osteosarcomas and 49% for chondrosarcomas after neutron irradiation; the corresponding values are 21% and 33% respectively after photon irradiation. For locally extended prostatic adenocarcinoma, the superiority of mixed schedule (neutrons + photons) was demonstrated by a RTOG randomized trial (local control rates 77% for mixed schedule compared to 31% for photons). Neutrons were also shown to be useful for palliative treatment of melanomas. Further studies are needed in order to evaluate the benefit of fast neutrons for other localisations such as cervix, bladder, rectum. It can be concluded that fast neutrons are superior to photons for at least 10% of the radiotherapy patients. It is likely that the new high- energy hospital-based cyclotrons will further extend the indications of neutron therapy. However, patient selection remains one of the main problems and there is a need for development of individual predictive tests.

Adenocarcinoma↗