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Biomedical subjects

A Mazal

Publications and source records attributed to A Mazal.

31 records · Page 2Linked to original sources
PubMed1996

[Quality assurance in protontherapy: a systematic approach in progress at Orsay].

The degree of accuracy and reliability required in proton therapy can only be guaranteed if a comprehensive quality assurance (QA) programme is established. Such a programme obviously has common features with general QA in radiotherapy, but some aspects are specific to the use of protons and particularly to the characteristics of each facility. A study is in progress at Orsay to convert a series of quality controls into a systematic quality assurance programme. It includes some basic steps on organisation, setting up a QA committee and QA task groups, organising meetings, policies, procedures, records, qualifications, and determining some examples of tolerance in controls. Among some critical and specific points identified in this process are the combined treatment with photons at different institutions, the specificity of a non-hospital-based and complex facility, the high degree of precision required for the patient setup, and the need to develop in-house basic tools such as the treatment planning system. The inclusion of all the patients in prospective well-defined clinical trials, the comparison with alternative techniques and the radiobiological studies are considered as fundamentals for the QA programme. Present dosimetric and radiobiological intercomparisons between protontherapy centres are considered as partial audits. A study is in progress to establish common dosimetric and clinical protocols, radiobiological models and dose and volume specifications. In spite of the differences between the existing facilities, it should also be possible to obtain international consensus on general guidelines for a QA programme in proton therapy.

Clinical Competence↗
PubMed1996

Clinical applications of proton therapy.

Proton therapy offers considerable potential advantages in the management of poorly resectable, radio-resistent tumors close to critical anatomical structures. So far over 15,000 patients have been treated worldwide with two major indications: conservative management of ocular melanomas in which local control exceeds 95% at 5 years and curative irradiation of sarcomas at the base of the skull and cervical canal, with a survival rate between 84 and 94% at 5 years. The different protocols tested currently worldwide are discussed.

Adolescent↗
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

Clinical applications of proton therapy. Experiences and ongoing studies.

Proton therapy offers potentially considerable advantages in the management of slow-growing, poorly resectable or non-resectable tumors resistant to x-rays and located close to critical radiosensitive anatomical structures, such as the brain stem of the spinal cord. Among over 13,000 irradiated patients in the USA, Europe, and Japan, two major clinical indications have been documented: 1. The conservative management of choroidal melanomas, in which 98% 5-year local control can be expected at the price of low toxicity and visual preservation in approximately half of them. 2. The curative management of low-grade chondrosarcomas and chordomas of the base of the skull and cervical spine, leading to, in combination with maximal tumor resection, 84%-94% long-term survival. Other ongoing studies concern prostate, head and neck carcinomas as well as various intracranial tumors. Radiosurgical programs are being conducted generally with single fractions and under stereotactic conditions.

Bone Neoplasms↗
PubMed1995

[Which equipment for proton therapy of the future?].

The success of proton therapy depends on its cost. Hospital based equipment in fabrication for the Massachusetts General Hospital in Boston costs in the excess of 17 millions dollars, the accelerator being only a fraction of the cost. We think that price can be significantly decreased. We review the different new ways of accelerating protons currently under study in France in order to build a smaller, less expensive but reliable treatment device.

Cyclotrons↗
PubMedDate not supplied

[Radiotherapy using a combination of photons and protons for locally aggressive intracranial tumors. Preliminary results of protocol CPO 94-C1].

PURPOSE: From October 1993 through July 1998, 48 assessable adult patients with non-resectable aggressive intracranial tumors were treated by a combination of high dose photon + proton therapy at the Centre de Protonthérapie d'Orsay. PATIENTS AND METHODS: Grade 1 and 4 gliomas were excluded. Patients benefited from a 3D dose calculation based on high-definition CT and MRI, a stereotactic positioning using implanted fiducial markers and a thermoplastic mask. Mean tumor dose ranged between 63 and 67 Gy delivered in five weekly sessions of 1.8 Gy in most patients, according to the histological types (doses in Co Gy Equivalent, with a mean proton-RBE of 1.1). RESULTS: With a median 18-month follow-up (range: four-58 months), local control in tumors located in the envelopes and in the skull base was 97% (33/34), and in parenchymal tumors, 43% (6/14) only. Two patients (5%) presented with a clinically severe radiation-induced necrosis (temporal lobe and chiasm). CONCLUSION: In our experience, high-dose radiation combining photons and protons is a safe and highly efficient procedure in selected malignancies of the skull base and envelopes.

Adult↗
PubMedDate not supplied

[Dosimetry of small-size photon beams].

A high performance standard radiotherapy treatment unit could be used to perform stereotactic radiosurgery. The dosimetric aspects of stereotactic irradiation with small size photon beams (energies from 5 to 25 MV produced by electron linear accelerator or gamma-rays produced by cobalt-60 treatment unit) are analyzed. The diameter of circular beams used are 5 to 40 millimeters wide at the isocenter of the treatment unit. The dosimetry of small x-ray fields is complicated by two factors: the relationship between detector size and field size dimensions, and the lack of lateral electron equilibrium. The large dose gradients outside the beam's central axis require dosimetry techniques with higher spatial resolution. To determine the best dosimetry system for measurements at the beam's small focal point, particularly for measurement of the field size dependent on output factors, several different detectors were investigated: ionization chamber, silicon diode, diamond detector, thermoluminescent dosimeter, and film. Ionization chamber, which presents a sensitive volume smaller than 0.02 cm3, is the most commonly recommended detector for field diameter above 8 mm. Current representative examples of dosimetric measurements for different x-ray energies, including percent depth dose, tissue maximum ratios, beam profiles (off axis ratios), and output factors, are presented and discussed. As well, the dosimetric characteristics of small photon beams are detailed.

Photons↗