Biomedical subjects

A Bridier

Publications and source records attributed to A Bridier.

At least 19 recordsLinked 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

Consequences of two different doses to the lungs during a single dose of total body irradiation: results of a randomized study on 85 patients.

PURPOSE: To evaluate the incidence of lung complications and leukemia recurrences after two different doses to the lungs during total body irradiation. METHODS AND MATERIALS: Seventy-nine patients with acute leukemia (AML or ALL) in first complete remission or chronic myeloid leukemia in the chronic phase, five patients with high grade lymphoma, and one with chronic lymphocytic leukemia were entered in the study. They were given a single dose of total body irradiation (10 Gy over 4 h) with two different doses to the lungs (6 Gy or 8 Gy) prior to bone marrow transplantation. The median dose rate was 0.04 Gy/min. The median follow-up for both groups of patients was 24 months. RESULTS: The actuarial 5-year overall survival rate was similar in both groups, 59% and 43% for patients given 8 Gy and 6 Gy to the lungs, respectively. The lung complication rate was similar in the two groups (28% vs. 22% for the 8 Gy and 6 Gy group, respectively). The actuarial leukemia recurrence rate was significantly higher in the group of patients given 6 Gy to the lungs (25%) vs. 0% in the 8 Gy group. Interestingly, all recurrences occurred in the group of patients who were given 6 Gy to the lungs, who had acute leukemia, and no chronic graft vs. host disease (GVHD). CONCLUSIONS: Although the number of patients was not very large and the follow-up relatively short, these findings suggest that a lower dose to the lungs could lead to an increased incidence of leukemia recurrences due to a lower dose to the thoracic wall or to lower incidence of chronic GVHD.

Adolescent↗

PubMed1994

Secondary solid malignant tumors occurring after bone marrow transplantation for severe aplastic anemia given thoraco-abdominal irradiation.

PURPOSE: We have evaluated irradiation doses received at location of secondary solid tumors occurring after bone marrow transplantation (BMT) in five of 147 patients grafted for severe aplastic anaemia. RESULTS: All 5 tumors occurred within the radiation field penumbra. The estimated received dose varied from 6 Gy for one inner field secondary tumor, to 2.5 Gy for the remaining secondary tumors. CONCLUSION: Tumors may arise in the zone where the delivered radiation dose drops dramatically. Irradiation, with associated cofactors, may promote the development of epidermoid carcinoma in irradiated patients for BMT.

Abdomen↗

PubMed1993

Principles and techniques of irradiation for the N0 neck.

The absence of palpable lymph nodes is one of the important elements in the choice of treatment of head and neck cancers. Irradiation of the neck represents one possible treatment chosen on the basis of historical, clinical and biological arguments. Currently available techniques for irradiation at the Gustave Roussy Institute are reviewed.

Head and Neck Neoplasms↗

PubMed1993

Characteristics of contamination electrons in high energy photon beams.

A simple method to estimate the contribution of contaminating electrons to the dose, and to evaluate their dosimetric characteristics is proposed. The method is based on a normalisation of the tissue--maximum ratio curves to a constant primary photon fluence. The contribution of the contaminating electrons to the dose is calculated by subtracting the dose relative to a small field from the dose relative to the field under consideration. The method includes the determination of the mean energy, the linear apparent attenuation coefficient, the 50% range and the maximum range of the contaminating electrons. The extrapolated surface dose normalised to a constant primary photon fluence has been found to be constant for a constant collimator opening whatever may be the source distance.

Absorption↗

PubMed1993

EORTC radiotherapy group quality assurance: mechanical checks and beam alignments of megavoltage equipment.

In 1987 mechanical checks of megavoltage units and simulators were included in the on-site physics program of the EORTC. The results reported were obtained in 16 different centres and concern 23 accelerators, 14 cobalt units and 14 simulators. In general, the deviations observed for accelerators and simulators are smaller than for cobalt units. A single score, based on the deviations observed for the mechanical checks, is attributed to each centre.

Cobalt Radioisotopes↗

PubMed1993

A method for dose calculation for high energy photon beams based on measurements performed at reference depth.

An algorithm is proposed to calculate the dose per monitor unit at any point along the beam axis for blocked or unblocked fields. The proposed formalism takes into consideration the beam measurements performed at the reference depth as recommended by most dosimetry protocols (5 cm or 10 cm depending on the beam quality). The only parameters which cannot be measured at the reference depth are the peak scatter factors, but they appear only as a ratio of two peak scatter factors for two slightly different field sizes. A correction factor is proposed when the distance of one shielding block to the beam axis is smaller than 5 cm. An agreement better than 1% has been obtained between calculations and measurements in the range of beam qualities, distances to the source and field sizes defined by typical collimators or shielding blocks, usually encountered in clinical practice.

Calibration↗

PubMed1992

Influence of shielding blocks on the output of photon beams as a function of energy and type of treatment unit.

The influence of field-defining shielding blocks on the output of a cobalt unit and of seven different accelerators (one with dual energy output) has been investigated. The quality indices range from 0.57 (cobalt-60) to 0.79. The loss in output due to shielding blocks has been calculated taking into account loss in phantom scatter only. Comparison with experimental results shows that the calculation algorithm is correct in most of the clinical conditions. However, for quality indices of 0.70 and higher, for blocks close to the central beam axis, an overestimation of the output by the algorithm has been found. The maximum deviation observed is about 5% for the highest energy and for block positions corresponding to those applied, e.g. for inverted Y-fields with narrow lumbo-aortic block spacing.

Algorithms↗

PubMed1990

Dosimetry for total body irradiation.

Basic dosimetry as well as patient dosimetry are considered. The following items concerning the basic beam dosimetry are discussed: dosimetry calibration, phantom material, beam quality and depth dose measurements in TBI conditions. Dose to the patient should be specified to the midplane of the abdomen but dose to the lung should be estimated for each patient. In vivo, dosimetry is strongly recommended for determination of dose homogeneity, as well as to check patient position, reproducibility of treatment and instabilities in dose rate during TBI. Many physical problems are associated with in vivo dosimetry. All influences on the detector response have to be considered and the detectors must be calibrated for TBI conditions.

Absorption↗

PubMed1987

Prospective comparison of ultrasound and computed tomography in the evaluation of the size of the uterus: can these methods be used for intracavitary treatment planning of carcinoma of the uterus?

A prospective evaluation of computed tomography and ultrasound was performed on 34 patients with Stage I and II endometrial carcinoma. All patients underwent immediate surgery following intracavitary treatment directed to vaginal mucosa. Pathologic measurements of the uterus were compared to those obtained by imaging technologies. The results of the study suggest that all but height measurements were rather accurately determined by both ultrasound and CT scan. However ultrasound was significantly better in determining the size of the cervix. Therefore ultrasound measurements could be used routinely for intracavitary treatment planning in endocervical carcinoma and endometrial carcinoma.

Brachytherapy↗

PubMed1986

On the use of a quality index to specify high energy photon beams.

It is important to specify the beam quality in a simple and nonambiguous way in order on one hand to make comparisons easier between treatments performed in various hospitals, or at different times in the same hospital and on the other hand to facilitate the choice of numerical values for factors like restricted mass-collision stopping-power ratios and perturbation correction factors used in the conversion of ionization measurements into absorbed dose. We have adopted for high-energy photon beam specification a quality index (I) defined by the ratio (I20/I10) of ionizations measured with a constant source-detector distance for a reference field size 10 X 10 cm2. We have found that this quality index is independent of the source detector distance. On the other hand, the apparent linear attenuation coefficient measured on the exponential part of the tissue-maximum ratio curve can be calculated for any field size from the value of I for most high energy photon beams. In order to check the validity of the quality index for other linacs from other manufacturers, we have compared our results to published data related to various photon beams in a wide energy range: 2.5 to 45 MV.

Humans↗

PubMed1986

A comparison of build-up and depth dose characteristics of different photon beams for the treatment of Hodgkin's disease.

Measurements have been performed of build-up and depth-dose characteristics of photon beams under Hodgkin's disease treatment conditions as applied in two hospitals (AVL, Amsterdam and IGR, Villejuif). Although different types of accelerators, photon energies, field sizes and SSD are employed, similar dose distributions along the beam axis have been obtained in both centers. In order to explain this unexpected good agreement, the influence of the geometrical conditions of irradiation on the build-up and depth-dose distribution has been studied in detail for five photon beams (8 MV-25 MV) of three types of accelerators.

Evaluation Studies as Topic↗

PubMed1986

Biologic and anatomic problems of lung shielding in whole-body irradiation.

Lung shielding by lead blocks for reducing the dose to the lungs in whole-body irradiation results in relative protection of the leukemia cell population. The consequence is acceptable if the dose reduction is moderate (from 10 to 8 Gy) and if the shielded volume amounts to a small fraction (5%) of the body weight. The suggestion was made that certain limits should be put on the extent of shielding, so that the shielded lung fraction represents only 60% of the total lung volume.

Humans↗

PubMed1984