Progress in inter-departmental audit: the Midlands experience

In ensuring the safety of patients in radiotherapy problems can arise from systematic errors in: the basic data, beam calibration, treatment planning or in the regular measurement of machine parameters. One possible method of identifying any such problems is by the use of an audit carried out by another department. In order to devise and test an audit system a co-operative venture between the physics departments at the Walsgrave Hospital, Coventry and the Leicester Royal Infirmary was initiated in 1991 and reported by us at the last biennial meeting. The audit was confined to external beam therapy i.e. electron and photon beams and each audit covered only one machine and one modality. This pilot audit proved to be highly practical, cost effective and of definite benefit. This has now been extended to include the 9 other centres which cover the (English) Midlands: Birmingham, Coventry, Derby, Leicester, Lincoln, Nottingham, Northampton, Stoke-on-Trent and Woverhampton. The group has now been operating for three years, each annual cycle starting in May. In 1993/94 the auditors identified 67 aspects of local Quality Assurance procedures and records which required attention: 29 in basic dosimetry, 23 in machine performance and 15 in machine calibration. In no case was any of these serious. There was considerable variation in the range and frequency of the various checks performed. The errors in the depth doses and field factors measured were in the range -5.5 to +3.5 %. In the planned treatment to a trapezoidal water phantom the errors were in the range -4.0 to +2.0 %. The larger errors occurred only in extreme conditions, which this particular audit is designed to test, and would not have had any significant clinical effect. Nevertheless, a number of possible improvements in depth doses, beam profiles and treatment time calculations were identified. The presentation will include the results of the 1994/95 audit and will discuss any identifiable trends over the three years of its operation. Further development will include extension to brachytherapy and to Kv x-rays. A pilot brachytherapy audit between Leicester and Coventry using thermoluminescent dosemeters took place in 1994. One problem identified is the difficulty of obtaining reliable, accurate calibration factors for caesium-137 and indium-192 gamma rays