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J Chavaudra

Publications and source records attributed to J Chavaudra.

At least 37 records · Page 2Linked to original sources
PubMed1995

An experimental approach to the design of a scattering system for a proton therapy beam line dedicated to ophthalmological applications.

PURPOSE: The development of a scattering system for a proton therapy beam line dedicated to ophthalmological applications. METHODS AND MATERIALS: A protontherapy beam line has been developed for the treatment of uveal melanoma at the Orsay synchrocyclotron. The original 200 MeV proton beam is degraded to 76 MeV and the final beam characteristics (range, modulation, flatness, collimation) are obtained with beam modifiers in the treatment room. A passive scattering system is used to obtain a uniform dose distribution in the beam cross-section throughout 30 mm in diameter, with minimal losses in energy and dose rate. We have used an experimental approach for the scattering study. RESULTS: An elliptical ring shaped from 0.1-mm thick lead is the solution we have adopted for the scattering system. For a modulated beam, a flatness of 1% is obtained on transverse profiles. The energy loss introduced by this scatterer is only 0.5 MeV, with no appreciable change in the range over the treatment field. For an unmodulated beam, 21% of intensity is lost when the scatterer is used. The distal and the lateral dose fall-off (90-10%) for a modulated beam are 2.6 mm. These last values are independent of the range and the modulation currently used for the ophthalmic applications. CONCLUSION: A specific passive scattering system can be adapted to a particular beam emittance. A systematic experimental approach can easily be undertaken to obtain the scatterer adapted for small irradiation fields in proton therapy.

Equipment Design↗
PubMed1995

A European quality assurance network for radiotherapy: dose measurement procedure.

In the frame of the experimental implementation of a European quality assurance network for external radiotherapy, the methodology in the European Measuring Centre (MC) is presented. Mailed TL dosimeters are used for the check of the beam output and of the beam quality of photon beams. The thermoluminescent material is PTL 717 LiF powder. The readings were first performed on a manual, and then on an automatic reader, with standard deviations of the mean of 0.7% for one dosimeter. Corrections for supralinearity and for the energy dependence of the dosimeter response are applied. An original method has been developed to correct for the variation of the LiF response as a function of time. It is shown that the sensitivity of the powder changes during storage, leading to a kind of 'inverse fading'. The global uncertainty of the TL postal measurement procedure is estimated to be about 1.5% for the 60Co beams and 2% for the x-ray beams. Intercomparisons with the IAEA and with the EORTC have shown an agreement better than 2% for all energies. It can be concluded that the results of the MC are suitable for the requirements of a European quality assurance network.

Cobalt Radioisotopes↗
PubMed1994

Quality control of radiotherapy centres in Europe: beam calibration.

A European Quality Assurance Network for external radiotherapy was set up. In this, several countries participated on a voluntary basis to elaborate common protocols, using joint infrastructure. The support for the co-ordination of the project was given by the EC committee 'Europe Against Cancer'. In the first step of the programme, beam outputs and beam qualities are checked with mailed thermoluminescent dosimeters following the protocol prepared by the IAEA. The results concerning 125 beams from 66 centres are analysed. Twenty-two beams presented minor deviations (3-6%) and 15 beams (4/48 60Co beams and 11/77 X-ray beams) from 11 centres presented major deviations (> or = 6%). The analysis shows that 16/22 minor deviations and all major deviations have been detected in centres which have not benefited from an external check during the last 5 years. In 14 out of 15 large deviations, the measured dose was smaller than the stated dose. In most centres with major deviation the physicists did not have the necessary experience and did not regularly calibrate the beams. In 6 out of 11 centres there was no dosimeter or the dosimeter available had not been calibrated recently. In 3 centres, the physicist did not give any explanation.

Calibration↗
PubMed1994

[Evaluation of individual dosimetric data on patients in an international radiotherapy trial].

A quality control programme has been developed in the radiotherapy department of the Institut Gustave-Roussy for an international clinical trial on the use of Etanidazole as a radiosensitizer in association with radiotherapy for head and neck tumors. Twenty-nine european centers belonging to Germany, United Kingdom, Austria, France and Italy contributed to this trial during 374 patients has been included from 1987 to 1988. This programme concerned the control of the external radiotherapy equipment available in the participating centers and the examination of the patient treatment data. The authors present, in this paper, the methods applied and the main results obtained during the analysis of the individual patient treatment data. This analysis shows that 83% of the evaluable treatments were done in compliance with the protocol recommendations and 17% contained a major deviation and among them only 3% were judged unacceptable.

Humans↗
PubMed1993

Preliminary results of a quality assurance network for radiotherapy centres in Europe.

Based on the IAEA/WHO experience in mailed dosimetry, a Quality Assurance (QA) Network, sponsored by the EC committee "Europe Against Cancer", has been set up in 1991 for European centres, not involved in clinical research. Besides a survey of radiotherapy infrastructure, the project includes three measurement steps: primarily a check of beam output and quality in reference conditions with a mailed TLD-procedure, in a second step the mailed verification of other beam data and dose calculation procedures with a multipurpose phantom and finally in vivo dosimetry at the individual patient levels with mailed dosimeters. The results of infrastructure show good agreement with the data previously published by EORTC for research centres. Until January 1993, a total number of 37 centres (49 X-ray beams and 28 cobalt beams) from Belgium, France, Italy, The Netherlands, Sweden and The Czech and Slovak Republics have participated in the first measurement step. Deviations > 3% and < 6% from the stated dose are found in 17 out of the 79 checked beams. A deviation < 6% from the stated dose is detected in only 1 out of the 28 cobalt beams, but in 7 of the 49 X-ray beams. The large majority of the beams (23/25) with deviations > 3% belong to centres not having participated in external audits in the previous 5 years. A pilot study for the second step shows larger deviations in non reference conditions, especially for off-axis points and for oblique phantom surface. The third step has yet to be implemented.(ABSTRACT TRUNCATED AT 250 WORDS)

Europe↗
PubMed1992

Retrospective evaluation of the dose received by the ovary after radioactive iodine therapy for thyroid cancer.

In an earlier study, we evaluated the frequency of clinical manifestations of ovarian insufficiency after radioiodine therapy for thyroid cancer. We were thus led to consider the dose received by the ovary (DRO) during these treatments. In the literature, this dose is expressed as a function of the activity administered. However, in our study, the disorders were not correlated with the activity administered. Faced with this discrepancy, we have attempted to establish a dosimetric model using the parameters available for each patient. The results obtained show that besides the activity administered, which plays a role, morphological and kinetic factors specific to each individual have an importance that cannot be ignored when addressing this problem.

Female↗
PubMed1991

Breast cancer treatment: which inhomogeneities have to be taken into account?

A true three-dimensional algorithm has been developed at the Gustave Roussy Institute, which can evaluate the dose distribution in inhomogeneous media. In this paper, an explanation is given that, in our view, problems of inhomogeneity cannot be solved without accounting for the third dimension and its contribution to scattered dose calculation.

Algorithms↗
PubMed1988

[Management in cases of accidental contamination by iodine radioisotopes].

Iodide can reduce radioactive iodine thyroid uptake and whole-body irradiation. Maximal effectiveness is obtained when 3 conditions are fulfilled: adequate dosage: potassium iodide 130 mg (i.e. iodide 100 mg) as tablets in adults and older children, 50 mg in infants under one year of age; prompt administration after contamination and daily treatment as long as the contamination persists. Depending on the importance and duration of the contamination, different dosages may be required. In any case, children must be given priority for prophylactic measures.

Accidents↗
PubMed1983

Biological effects and irradiation dose induced in human lymphocytes in vitro by an intracellular radionuclide:99mTc.

Since lymphocyte radiolabeling is widely used for in vitro and in vivo studies and may interfere with the properties of the cells, the purpose of this work was to investigate the effects of 99mTc labeling on lymphocyte morphology and functions. Two ranges of 99mTc activity were used, 37 and 370 MBq, and their effects were compared to those produced by a graduated external irradiation. Electron microscopy was performed and T cells were studied using biological markers (E-Rosette formation, cell proliferation under lectin reactivity, and specific cell-mediated cytolysis). After 370-MBq labeling, an intense cytotoxic effect was observed on cell morphology, drastically impeding T-lymphocyte functions. Thirty-seven-megabecquerel labeling and sham procedure did not significantly affect cell functions. The external irradiation dose-response curve indicated a clear radiation-induced inhibitory effect, especially over 10 Gy. This effect was less intense than that obtained with 370-MBq 99mTc labeling. The labeling cytotoxic effect can then be attributed to a radiolesion due to a radiation dose which is probably higher than 10 Gy. In fact, the dose received by lymphocytes during the 370-MBq labeling procedure was estimated as 70 Gy by calculations, taking into account all emissions of 99mTc.

Humans↗
PubMed1977

[The value of routine in vivo measurements in radiotherapy (author's transl)].

The authors carried out routine measurements in vivo, and emphasise their value in radiotherapy. After reviewing the objectives of in vivo measurements in general, and showing the problems posed by routine measurements, they describe the technique of measurement using thermoluminescent dosimeters and the problems associated with their use in patients treated with the aid of a 5.5 MV linear accelerator. Results based upon 232 routine measurements made it possible to establish a correlation between the dose delivered and the expected dose. Under optimal functional conditions, almost all the deviations seen were less than 5% whilst higher deviations occurred when the apparatus showed signs of instability. They conclude that routine in vivo measurements are extremely useful in ensuring that planned treatment is carried out in a satisfactory manner and also in the early detection of potential faults in equipment.

Humans↗
PubMed1976

[Practical use of lithium borate in thermoluminescent dosimetry (author's transl)].

The authors recall the functional principles of thermoluminescent dosimeters: heating, apparatus for measuring the emitted light, circulation of nitrogen, reference source. They take this opportunity to stress the essential role played by the circulation of nitrogen over the dosimeters which equilibrates the temperature of the photo multiplier, reduces the emission of unwanted light, prevents the combustion of dust or other possible impurities and finally improves the reproductibility of the measurements even for high dosod for finding the optimum working conditions for the heating apparatus of the planchette in the most simple T.L.D. readers and in those where the heating apparatus of the planchette has a pre-heating phase. They then study the dosimetric properties of lithium borate incorporated in thin teflon discs (type DLB. 0.13 and 0.4). This shows itself to be very interesting for certain uses because it is a solid dosimeter which does not require annealing between two measurements. The reproductibility of the measurements obtained with this material, the stability of its response relative to the delay between radiation and reading (fading), its response relative to the absorbed dose plus the nature and the energy of the rays, are presented with the usual reservations made for this type of dosimetry. The authors conclude by citing a few applications where they have been able to achieve a satisfactory result with the aid of lithium borate.

Borates↗