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7. Consideration of the findings of a previous investigation into the conduct of Isocentric Radiotherapy at the North Staffordshire Royal Infirmary between 1982 and 1991
7.1 Introduction
7.1 When incidents such as the one under investigation here occur, it is relevant to ask whether the risk of occurrence might have been reduced by proper attention to the lessons available from previous incidents.
7.2 Between 1982 and 1991 just under 1000 patients who underwent isocentric radiotherapy treatment at the North Staffordshire Royal Infirmary ( NSRI) received a dose of radiation significantly less than intended. This led to the commissioning by the West Midlands Regional Health Authority of an independent inquiry headed by Sir Peter Baldwin. The first report of this inquiry was published in August 1992 and this was followed by a second report in March 1994. This second report included consideration of the findings of an Independent Clinical Assessment of the affected patients that was commissioned by North Staffordshire Health Authority and published in September 1993.
7.3 While there are some very obvious differences between the circumstances of the North Staffordshire incident and that considered here, the parallels and the extent to which any lessons learned from this previous incident could have affected practice at the BOC are worthy of consideration.
7.2 The causes of the North Staffordshire incident
7.4 'Isocentric' radiation treatment involves rotation of the treatment machine in a plane around the patient whereby the centre of rotation is coincident with the target tumour. The aim is to deliver a predetermined dose of radiation to the target from different angles and treatment planning is complex. Prior to 1982 the absence of a treatment planning computer at NSRI meant that calculations of complete dose distributions for isocentric treatments were not practical.
7.5 One of the difficulties for planning of isocentric treatment is that the beam intensity required to deliver the correct dose to the target depends on the distance between the source and the skin of the patient and this changes on machine rotation. Therefore an appropriate allowance needs to be made.
7.6 Prior to 1982, the Treatment Radiographer at NSRI was familiar with the need to adjust the beam intensity for non-isocentric treatments where the distance between the source and the skin was other than 1 metre. Therefore, when the new computer system was introduced in 1982, the Treatment Radiographer assumed that this adjustment was still required and convinced the Physicist responsible for treatment planning that this was the case. What both failed to recognize was that the new computer software already incorporated an allowance for source to skin distance in its calculation of beam intensity.
7.7 The Treatment Radiographer's concern over the need to make the manual adjustment is understandable in that, had this indeed been needed and omitted, then serious overexposures could have resulted.
7.8 The result of this initial error was that the allowance for distance made by the computer was duplicated manually by the Treatment Radiographer and this duplication continued for all isocentric treatments between 1982 and 1991.
7.3 Findings of the Baldwin Report relevant to the BOC incident
7.9 It is informative to consider what parallels can be identified in the circumstances of the NSRI incident and that at the BOC.
| The NSRI incident. | The BOC incident. |
|---|
| A change was made to the treatment planning software ( RTPLAN) but the full implications were not evaluated formally. | A change was made to the treatment planning software (Varis 7) but the full implications were not evaluated formally. |
| The change related to the complex procedure of isocentric radiotherapy. | The change had specific implications for certain complex procedures including whole CNS treatment. |
| Following the change, radiotherapy staff continued to use a method of manual adjustment of the MU output from the new software to allow for source to skin distance. The change had rendered this adjustment unnecessary. | Following the change, treatment planning staff continued to use a paper form that required an entry in MU per 100 centiGrays. This now required manual normalization of the MU output from the new software but the planner was not aware of this need. |
| The error resulted in the wrong number of monitor units being set on the delivery unit. | The error resulted in the wrong number of monitor units being set on the delivery unit. |
| The error remained undetected for some 9 years and, as a result, some 1000 patients received doses of radiation much less than intended. | The error was detected in preparation of the next, similar plan and, as a result, only one patient received a dose of radiation much greater than intended. |
| During investigation, treatment planning staff expressed concerns that the staffing arrangements prevalent at the time of the incident left little time for quality assurance measures. | During investigation, treatment planning staff expressed concerns that the staffing arrangements prevalent at the time of the incident left little time for quality assurance measures. |
7.10 There were, therefore, a number of similarities between these two incidents but of principal note is that both stemmed from the introduction of a change to the computer system without formal and detailed evaluation of its full implications. In both cases, had there been a formal requirement for evaluation of significant changes that might affect the dose delivered to the patient, then the incidents might have been avoided.
7.4 Recommendations of the Baldwin Report relevant to the BOC incident
7.11 Part of the remit of the independent inquiry into the NSRI incident was 'To make recommendations for updating and reviewing policies and procedures in the light of the current incident.' The emerging recommendations included the following:
(i) It should be the duty of the Principal Radiotherapy Physicist to institute such a programme or programmes of tests and checks, recurrent or otherwise, that each Clinical Oncologist in the Department is continually assured that any dose of radiation which he or she prescribes is delivered to the tumour in precisely the manner and the intensity prescribed by the physician.
(ii) In the event of any new equipment or any new processes being considered for introduction into the work of the Radiotherapy Department, the top management of the Acute Unit should consider what arrangements for training would provide assurance against error, whether on the part of Clinicians, Radiotherapy Physicists, Radiographers or supporting staff; and should draw on resources outside the Acute Unit if there is any reason to believe that those within the Unit would not suffice.
(iii) No equipment should be allowed to enter into use within the Department without manuals explaining both its operation and the significance in its operation of the scientific understanding which it is the purpose of the equipment to utilise.
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