A survey of radiotherapy quality control practice in the United Kingdom for the START trial.

BACKGROUND AND PURPOSE: This paper compares the quality control checks performed in departments in the United Kingdom with those recommended by the Institute of Physics and Engineering in Medicine (IPEM) in Report 81. METHOD: The data were gathered by the quality assurance team for the START trial, during visits to individual departments. Data are compared with the frequencies suggested in IPEM report 81. Where applicable, data are also analyzed with respect to machine manufacturer. RESULTS: All departments with linear accelerators check the output at least weekly for both photons and electrons, however 11% of departments do not perform a constancy check of the output on a daily basis. The majority of departments check flatness at gantry zero on a monthly basis. However 27% of departments never check at non-zero gantry angles. In 51% of departments no fluoroscopy checks are performed on simulators on a daily basis. CONCLUSION: The majority of departments are following the frequencies suggested in IPEM report 81 although there are a number of discrepancies particularly for simulators. Accelerator type needs to be considered when designing quality assurance checks. In many departments more time than is currently allocated is needed on equipment, particularly simulators, to complete all of the checks suggested in Report 81.

The START trial-measurements in semi-anatomical breast and chest wall phantoms.

This paper describes dosimetry measurements performed prior to departments entering patients into the START Trial, a breast fractionation trial. Absolute and relative doses were measured in semi-anatomical breast and chest wall phantoms, as part of a quality assurance programme visit. Doses were measured using an ionization chamber and the resulting distributions were compared with those calculated by the department. The mean ratio of measured to calculated dose at the START reference point was found to be 0.981 for the breast phantom and 0.978 for the chest wall phantom. This average measured dose was significantly less than the prescribed dose (p < 0.001). Differences were found between 2D and 3D planning systems and for departments using cobalt 60 beams. A number of departments had deviations of greater than 4%, which was the tolerance applied for this trial. It is essential for dose measurements of this type to be performed for randomized clinical trials involving radiotherapy, particularly where dose fractionation regimes are being compared.

Breast radiotherapy phantom design for the START trial. START trial management group.

The design of phantoms for use in radiotherapy involves a number of complex issues. This paper describes breast and chest wall phantoms that have been designed and constructed for the START trial. Four phantoms have been manufactured, including two two-dimensional phantoms used on the first round of audit visits to assess the ability of departments to plan with the required accuracy. Two further phantoms have been constructed and will be used in the second round of audit visits; one is a water-filled three-dimensional phantom for investigating off-axis dosimetry, the other is to be used to assess dose in the junction region between the tangential fields and the supraclavicular fossa field. The manufacturing and design process for each of the phantoms is discussed.

Survey of tangential field planning and dose distribution in the UK: background to the introduction of the quality assurance programme for the START trial in early breast cancer.

A background survey of UK breast radiotherapy techniques was performed prior to the introduction of the quality assurance programme for the Standardization of Radiotherapy (START) trial in breast cancer, a UK multicentre randomized trial of different dose fractionations for breast radiotherapy. Analysis of patient treatment plans was performed at this initial stage of the quality assurance programme to ensure eventual uniformity of treatment within the randomized trial and hence ensure reliable end results. As an integral part of this initial survey, three patient outlines of different size and shape were circulated between November 1997 and January 1998 to 56 UK radiotherapy centres. Dose distributions were produced according to the routine planning protocol of each department to provide information on treatment planning techniques. Criteria used for treatment plan production and the resultant dose distributions were analysed. The dose distributions varied between centres. Dose inhomogeneity of no more than 10% was achieved, on the central axis, for all chest wall and medium breast size plans. The number of larger breast size distributions exceeding a 10% dose gradient across the treatment volume was 54% (26). Most centres in the UK determine the breast dose distribution by planning on a two-dimensional contour taken along the central plane of the breast. Variation in the breast contour either side of this central plane is not taken into account. Care with plan optimization by selecting the most appropriate beam parameters can lead to an improvement in breast dosimetry.

Irradiation of the heart during tangential breast treatment: a study within the START trial.

Radiotherapy to the breast is often given as a component of the treatment for women with breast cancer. It has been shown to increase overall survival although an increase in cardiac mortality has also been noted. This study was undertaken as part of the START trial quality assurance programme to record and evaluate the cardiac dose using modern radiotherapy techniques. Departments randomizing patients into the START trial and who had CT facilities for planning breast patients were invited to take part. 62 patients were included. CT slices were taken at the level of the maximum heart depth and on the treatment field central axis. Each patient was planned in the normal way and the distributions were analysed by the quality assurance team at Mount Vernon Hospital. The maximum heart position was found to be inferior to the central axis used for breast planning for the majority of patients; mean position 2.3 cm inferior with a mean maximum heart depth of 0.55 cm. For 45% of patients the maximum heart dose was less than 50% of the prescribed dose. The study showed that the volume of irradiated cardiac tissue has decreased compared with earlier studies, and also highlighted the need to scan away from the central axis if the dose to cardiac tissue is to be assessed.

Survey of UK breast radiotherapy techniques: background prior to the introduction of the quality assurance programme for the START (standardisation of radiotherapy) trial in breast cancer.

As an integral part of a quality assurance programme, this survey was undertaken to establish precise details of breast radiation techniques used within centres expressing an interest to participate in the START Trial--a U.K. multi-centre randomised trial of different dose fractionation schedules for breast cancer. A questionnaire was circulated between November 1997 and January 1999 to 56 U.K. radiotherapy centres. This covered specific details of patient immobilisation, technique and dose fractionation when treating breast or chest wall, supraclavicular fossa and axilla and when directing a boost to the tumour bed. Variations in technique, incorporating immobilisation, treatment energy and dose prescription span the entire radiation treatment process from localisation to planning and subsequent treatment. A range of dose/fraction/time schedules were used for tangential fields, nodal fields and the tumour bed boost. As part of the quality assurance programme for the START Trial this independent review of breast radiotherapy practice has provided a baseline of techniques used by centres prior to participating in the trial. It has also presented a view of the complexity of the issues to enable the design of the next phase of the quality assurance programme. Adherence to the trial protocol will ensure acceptable technique and dosimetry across centres.

Developing algorithms to enhance the sensitivity of cancellation tests of visuospatial neglect.

We describe a set of algorithms that enhance the sensitivity of cancellation tests used in assessing visuospatial neglect. The algorithms can be readily implemented on a computer and can provide temporal and nontemporal data on strategies used during cancellation. We also present preliminary results from a group of 68 right-hemisphere brain-damaged patients and 12 age-matched control participants, which demonstrate the clinical significance of the measures we have defined.