Unintended overexposure of a patient during palliative radiotherapy treatment: investigation report

4. The nature of the error

4.1 The treatment received

Radiotherapy treatments are normally considered in two categories, 'radical treatment' where the aim is to achieve a cure, and 'palliative treatment' is where the aim is to improve the quality of life of patients by reduction in the size of the cancer or to relieve pain or other associated symptoms. This incident relates to a palliative treatment, one further feature of which is that whereas radical treatments involve individual outlining of a target (with the addition of small margins to allow for known planning and delivery conditions) the margins of the targeted treatment area for palliative treatment normally are bigger and less precisely delineated.

In August of 2017 a patient with breast cancer and with a 3-month history of hoarseness was referred by a General Practitioner to the Ear, Nose and Throat Department of NHS Lothian's University Hospitals Division. Examination showed left vocal cord palsy.

Since August of 2015, the patient was known to have had a metastatic left anterior hilar lymph node tumour invading the mediastinum (the central area between the lungs), and in August of 2017 a repeat CT scan showed that the size of this tumour remained unchanged.

The patient was then referred to the ECC and had a repeat CT scan on 28th November 2017 which showed an increase in the size of the tumour. The Clinical Oncologist who reviewed this scan (Clinical Oncologist A) therefore arranged for the patient to attend the relevant ECC oncology clinic on Monday 18th December 2018. The intent was that a suitable course of palliative radiotherapy aimed at reducing the left anterior hilar lymph node tumour should be considered.

At the oncology clinic, the patient was seen by Clinical Oncologist B. This was the first time that Clinical Oncologist B had met the patient.

The outcome of this consultation was that Clinical Oncologist B completed a standard ECC informed consent pro-forma for treatment of the 'Mediastinum' with the intent 'To shrink the hilar mass', which the patient then signed. The mediastinum was to be treated with the aim of alleviating the vocal cord palsy by targeting the enlarged hilar lymph node thought to be affecting the left recurrent laryngeal nerve.

Clinical Oncologist B then completed the standard ECC Radiotherapy Booking Form as the 'Referrer' and signed the justification section of the form as the 'Practitioner'. The 'Treatment Site' was completed on the form as 'Mediastinum', with no further elaboration of the particular area of the mediastinum on which the treatment should be focussed.

On the same day (Monday 18th December 2018) Clinical Oncologist B submitted a request for an 'ad-hoc'* treatment planning session and this was arranged for the morning of Friday 22 December 2018. (The term 'ad-hoc' is used by the ECC to refer to treatment planning sessions that are not part of the site specific scheduled weekly planning sessions.)

With regard to the IR(ME) Regulations, in addition to acting as 'referrer and 'practitioner' for the pre-treatment and treatment exposures, in carrying out the practical aspect of field placement, Clinical Oncologist B was also acting as an 'operator'.

The treatment prescribed by Clinical Oncologist B was a total dose of 20Gray (Gy) of X-ray radiation to be delivered to the mediastinum in 5 fractions, each of 4Gy.

The prescribed radiation dose, method of delivery, and fractionation were as expected for treatment of this condition, and in accordance with the relevant ECC Employer's Written Protocol for 'Clinical management guidelines for lung cancer'.

The patient commenced radiotherapy on 27 December 2017 and completed 5 fractions of radiotherapy on 4 January 2018.

On 4 January 2018, the patient complained of retrosternal pain radiating to the back and was seen by another clinical oncologist (Clinical Oncologist C). The diagnosis was radiation-related pain flare, and analgesia was advised.

On 21 January 2018, the patient was seen by the ENT Consultant who documented that the voice was much improved.

On 5 February 2018, the patient was reviewed by Clinical Oncologist A, who documented voice improvement and some mediastinal discomfort which had been present for approximately one week following completion of radiotherapy. The patient had no other new symptoms. A repeat CT scan was requested.

On 5 March 2018, the patient attended the follow-up clinic and was told by Clinical Oncologist A that the CT scan showed that the metastatic tumour in the left anterior hilar lymph lobe had increased in volume when compared with the scan conducted prior to the radiotherapy treatment. No other new sites of disease were identified. Since the result from this CT scan was unexpected following radiotherapy, Clinical Oncologist A arranged for the patient's imaging to be reviewed and for reassessment of the radiotherapy planning scan.

On 6 and 7 March 2018, Clinical Oncologist A together with another clinical oncologist from the relevant ECC Team (Clinical Oncologist D) reviewed the radiology and radiotherapy fields and found that the tumour in the left anterior hilar lymph lobe had not been covered by the radiotherapy. Therefore, the treatment given had no possibility of achieving the hilar mass shrinkage referred to in the completed consent pro-forma.

This report considers compliance with IR(ME) Regulations, the circumstances of these errors, and the measures necessary to minimize the risk of recurrence at the ECC and elsewhere.

4.2 Treatment Planning

Radiotherapy is a stepwise process that starts with clear identification of the size, shape, and position of the tumour (or other region of tissue) to be treated, followed by planning of how best to direct the radiation at the treatment site while avoiding damage to healthy surrounding tissue. The resulting plan is then used to direct the treatment machine (the 'Linear Accelerator' or 'Linac') in delivering the prescribed radiation dose.

In the Friday 22^nd December 2017 planning session the radiographers positioned the patient on a CT scanner and scanned the relevant part of the patient as described on the treatment prescription form. The images from this CT scan were displayed on a computer screen in the control area, whereon Clinical Oncologist B used the applicable software to define the borders or extent of the area for treatment.

This process is known as 'field placement' undertaken using virtual simulation software.

At the ECC, this information is then transferred to a system of lasers in the CT scanning room which identify the centre of the area for treatment on the skin of the patient. This point is then marked with a small tattoo. When the patient later attends for radiotherapy treatment, this tattoo defines the centre of the area or field that will be irradiated during treatment.

The treatment field defined by Clinical Oncologist B was a square measuring 10 by 10 cm.

When questioned as to why this field appears shifted to the lower right of the mediastinum (the initial concern having been for the left anterior hilar lymph node tumour) Clinical Oncologist B stated that at the time of viewing the planning CT images an area of concern to the lower right (possibly a further metastatic tumour) had also been noted. He therefore considered it clinically appropriate to place the treatment field so as to include this newly identified area.

Beyond this, Clinical Oncologist B, who confirmed awareness at the time of the need to cover the left anterior hilar lymph nodes, was unable to clarify further how the resulting field placement failed to do so. However, Clinical Oncologist B has since agreed that the most likely scenario was that in seeking to expand an initial field, which had been placed centrally on the mediastinum, by extending it to the lower right, this field was unintentionally shifted (rather than extended) by Clinical Oncologist B during the planning process and the error remained unnoticed by Clinical Oncologist B.