[The EQUAL-ESTRO external quality control laboratory in France].

Purpose: The EQUAL-ESTRO laboratory was set up in 1998 to perform external audits of radiotherapy beams for all the European centres. Until the end of the year 2003, it was funded by EC projects. The external quality control is based on measurements performed with thermoluminescent dosimeters (TLD) sent by postal mail to the participating centre in order to be irradiated on axis in reference conditions and in conditions close to clinical conditions for photon and electron beams.

The ESTRO-EQUAL Quality Assurance Network for photon and electron radiotherapy beams in Germany.

Background: In 1998 an ESTRO Quality Assurance Network for radiotherapy (EQUAL) has been set up for 25 European countries for photon and electron beams in reference and non-reference conditions.

Material And Methods: Measurements are done using LiF powder (DTL937-Philitech, France) that is processed with the PCL3 automatic reader (Fimel-PTW). The participating centers irradiate the TLDs with an absorbed dose of 2 Gy according to the clinical routine.

External audits of electron beams using mailed TLD dosimetry: preliminary results.

Aim: A feasibility study has been performed to investigate the possibility of using mailed thermoluminescence dosimetry (TLD) for external audits of clinical electron beams in Europe.

Methods: In the frame of the EC Network Project for Quality Assurance in Radiotherapy, instruction sheets and mailing procedures have been defined for mailed TLD dosimetry using the dedicated holder developed by a panel of experts of the International Atomic Energy Agency (IAEA). Three hundred and thirty electron beam set-ups have been checked in the reference centres and some local centres of the EC Network Project and in addition through the centres participating to the EORTC Radiotherapy Group trial 22922.

Energy correction factors of LiF powder TLDs irradiated in high-energy electron beams and applied to mailed dosimetry for quality assurance networks.

Absorbed dose determination with thermoluminescent dosimeters (TLDs) generally relies on calibration in 60Co gamma-ray reference beams. The energy correction factor fCo(E) for electron beams takes into account the difference between the response of the TLD in the beam of energy E and in the 60Co gamma-ray beam. In this work, fCo(E) was evaluated for an LiF powder irradiated in electron beams of 6 to 20 MeV (Varian 2300C/D) and 10 to 50 MeV (Racetrack MM50), and its variation with electron energy, TLD size and nature of the surrounding medium was also studied for LiF powder.

The ESTRO-QUALity assurance network (EQUAL).

Background And Purpose: ESTRO has set up a Quality Assurance network (EQUAL) to check the dose delivered on axis in reference and non-reference conditions for external radiotherapy. The external audits covered by the network are based on measurements made with mailed thermoluminescent dosimeters (TLD).

Material And Methods: The TLD consist of LiF powder type DTL 937 read with a PCL 3 automatic TLD reader.

Variation of relative transit dose profiles with patient-detector distance.

Background And Purpose: In view of using portal images for exit dosimetry, an experimental study is performed of relative transit dose profiles at different distances behind patients (and phantoms) and of their relation to the exit dose profile.

Materials And Methods: Irregular, homogeneous polystyrene phantoms with a variable thickness to simulate head and neck (H&N) treatments (6-MV photon beam) are investigated by ionization chamber measurements performed close to the exit surface and at various distances behind the phantom (10, 20 and 30 cm). Similar measurements are performed for a rectangular phantom with large inhomogeneities (A1 and air).

Radiotherapy of pelvic malignancies: impact of two types of rigid immobilisation devices on localisation errors.

Background And Purpose: To determine the distribution of set-up errors for patients treated with and without two rigid partial immobilisation devices for pelvic malignancies.

Materials And Methods: 30 patients receiving pelvic irradiation with a four field technique underwent a total of 524 portal films. The patients are divided into 3 cohorts of 10 patients.

Methods for beam data acquisition offered by a mini-phantom.

Mini-phantoms are an important tool for measurement of basic head scatter parameters in high-energy photon beams, and recently they have also been used for beam quality specification. Therefore the feasibility and reliability of basic beam parameter acquisition using only a mini-phantom is checked in 6, 18 and 25 MV photon beams. These parameters include head scatter correction factors, phantom scatter correction factors, total scatter correction factors, wedge factors, off-axis ratios, as well as beam attenuation coefficients and beam hardening coefficients.

Assessment of dose inhomogeneities in clinical practice by film dosimetry.

Aim: To use portal images acquired in routine circumstances for assessment of midplane dose variations in the patient.

Material And Methods: Optical density readings are performed on routinely acquired Verification films of breast and ear-nose-throat (ENT) cancer patients and these readings are converted into relative doses with the sensitometric curve. ( 1 ) The impact of redistribution is evaluated on films taken close to the patient exit surface and at routine focus film distance.

A quality assurance network in Central European countries--radiotherapy infrastructure.

A survey of the infrastructure in radiotherapy centres in three Central European countries has been performed as a first step in the development of a quality assurance network. Data concerning radiotherapy equipment, staff and number of patients treated in most of the radiotherapy centres from Czech Republic, Poland and Hungary were collected at the beginning of 1994. Equipment data have shown that 35% of 182 treatment units are conventional x-ray units, 35% 60Co units, 19% linear accelerators, 7% 137Cs units and 4% betatrons.

Output ratios in a miniphantom for asymmetric fields shaped by a multileaf collimator.

The integrated GE multileaf collimator (MLC) provides the ability to achieve 'double' asymmetric fields: each of the 64 leaves allow an over-axis travel of 10 cm and the Y-jaws allow 20 cm. A formalism has recently been proposed by the authors to calculate the output ratio in a miniphantom for this type of MLC by the product of independent leaf and jaw correction factors. The original proposed formalism was restricted to regular or irregular fields including the collimator rotational axis.

Dosimetric comparison of an integrated multileaf-collimator versus a conventional collimator.

The dosimetric characteristics of both a conventional GE collimator (CC) and a GE multileaf collimator (MLC) are compared for different photon beam energies. The integrated GE MLC consists of 32 pairs of tungsten leaves, replacing the lower pair of jaws of the conventional collimator. Measurements were performed with the conventional collimator before this collimator was replaced by the MLC.

Measurements of basic parameters in wedged high-energy photon beams using a mini-phantom.

Basic dosimetric quantities necessary to specify wedged beans (beam quality, wedge factors, output ratios) are obtained by measurements performed in a narrow coaxial mini-phantom for 6, 18 and 15 MV photon beams. To express beam quality, an attenuation coefficient mu is derived from measurements in a mini-phantom at 20 and 10 cm depth. Wedge factors and output ratios are measured as a function of field size at 10 cm water-equivalent depth.

External audit of photon beams by mailed film dosimetry: feasibility study.

A feasibility study for mailed film dosimetry has been performed. The global reproducibility of the method is better than 2%. It is shown that the normalized sensitometric curve does not depend on photon beam quality in the range from Co-60 gamma-rays to 18 MV x-rays, although the dose per optical density decreases when the energy increases.

A formalism to calculate the output ratio in a mini-phantom for a GE multileaf collimator.

A GE multileaf collimator (MLC) has been recently installed on a Saturne 43 and is used with 6, 18 and 25 MV photon beams. In the integrated GE MLC the lower pair of jaws in the X direction is replaced by 32 pairs of computer controlled opposed tungsten leaves. The influence of each set of leaves on the output ratio is smaller than the influence of the jaws it replaces (8% instead of 10%).

Quality assurance in brachytherapy: the role of the ICRU in achieving uniformity in dose and volume specification for reporting.

A quality assurance programme in brachytherapy implies a general consensus on the method of dose and volume specification for reporting. This in turn implies a consensus on certain definitions of terms and concepts. For several decades, the ICRU (International Commission on Radiation Units and Measurements) has been actively involved in an effort to reach a consensus between different brachytherapy centres worldwide, and to improve uniformity in reporting.

Quality assurance in radiotherapy: the importance of medical physics staffing levels. Recommendations from an ESTRO/EFOMP joint task group.

The safe application of ionising radiation for diagnosis and therapy requires a high level of knowledge of the underlying processes and of quality assurance. Sophisticated modern equipment can be used effectively for complicated diagnostic and therapeutic techniques only with adequate physics support. In the light of recent analyses and recommendations by national and international societies a joint working group of representatives from ESTRO (European Society for Therapeutic Radiology and Oncology) and from EFOMP (European Federation of Organisations for Medical Physics) was set up to assess the necessary staffing levels for physics support to radiotherapy.

The influence of the IAEA standard holder on dose evaluated from TLD samples.

The EROPAQ quality assurance project started in 1994 with TLD postal dose intercomparisons for photon beams used in 47 radiotherapy centres in the middle and eastern European countries. The photon dose intercomparisons include beam output checks and beam quality checks. Since an acceptance limit of +/- 3% was chosen for the EROPAQ intercomparisons, any systematic error in dose evaluation by the measuring centre should be minimized.

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.

Quality assurance network in central Europe. External audit on output calibration for photon beams.

The EROPAQ project for TLD monitoring of photon beams started in June 1994 with the set-up of the TLD system: calibration, reading and evaluation procedures. The acceptance level of +/- 3% was set for the TLD intercomparisons. The policy of the project was to check all beams in 47 participating radiotherapy centres and to recheck all the beams in those centres, where a deviation exceeding +/- 3% occurred in one or more of the beams.

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'.

Midplane dose determination using in vivo dose measurements in combination with portal imaging.

The possibility of using portal films in combination with semiconductor in vivo measurements for midplane dose distribution is investigated. A general algorithm, using measured entrance and exit doses and available beam data of the Linac, is proposed to derive the midplane dose for symmetrical inhomogeneities. Experimental verification of the algorithm with phantom measurements is performed for different kinds of inhomogeneities (Al, air and cork) and phantom thicknesses from 13 cm to 30 cm.

Reliability of clinical port films for measuring dose inhomogeneities in radiotherapy for head and neck tumours.

Reproducibility and reliability of film dosimetry are evaluated in clinical circumstances. Optical densities were read on 82 routinely taken verification films of Ear-Nose-Throat (ENT) treatment fields and corrected with the sensitometric curve to obtain relative dose values. Off-axis ratios measured on 10 successive films of one specific field were compared with each other and show a good reproducibility (s = 1.

Importance of in vivo dosimetry as part of a quality assurance program in tangential breast treatments.

Purpose: The investigation of the accuracy and reproducibility in the daily dose delivered in tangential breast treatments with in vivo dose measurements.

Methods And Materials: In vivo dose measurements performed on the tangential treatment fields of 35 breast cancer patients are analysed for three units: a 6 MV linear accelerator, an old Cobalt unit and a new Cobalt unit. The results are plotted in frequency distributions.