Session Item

Craniospinal irradiation (CSI) is used to treat medulloblastoma and other central nervous system tumours. The target volume includes the circulating cerebrospinal fluid and meninges, making this one of the most complex radiotherapy techniques delivered.

An unpublished Trust audit (RT2021_187) established that local CSI CTV-PTV margins could not be reduced without improvement to patient immobilisation. With little contemporary published guidance available on optimal immobilisation and treatment technique, the team undertook to elicit current CSI practice in the UK.

A 24-question survey was developed to capture CSI patient preparation, immobilisation, verification, and treatment planning techniques. The survey, on Microsoft forms, included yes/no, multiple-choice and open-ended questions. A survey link was e-mailed to radiotherapy service managers from National Health Service (NHS) centres, with a request to forward to an appropriate individual within their centre. In addition, the survey was publicised at SPRIGG, a national meeting for paediatric specialist radiographers and doctors.

The survey was open from 15^th Feb–19^th March 2021. Participation in the survey was voluntary without remuneration.

Twenty-six responses were received, 8 did not deliver CSI and 3 were duplicates. Duplicate answers were clarified, resulting in CSI data presented from 15 UK radiotherapy centres.

Most centres (13/15) treat paediatric and adult patients. Treatment under general anaesthetic is typically reserved for children ≤5-years (10/13), however, the child’s mental capacity and treatment technique used influences this decision. For patients requiring surgery prior to radiotherapy 5/15 centres allow 1-2 weeks before CT planning, however, this time ranges up to 6 weeks.

Five-point immobilisation shells are favoured for both adult (11/15) and paediatric (9/13) patients. For paediatric patients 8 centres routinely add a customisable head and neck cushion to personalise immobilisation. Painting paediatric shells is popular, 11 centres ‘always or sometimes’ decorate shells.

Torso immobilisation was used by 6/15 centres, utilising vac-bags. Ten centres ‘always or sometimes’ immobilised the patient’s pelvis, 7 with a knee rest and 3 with a vac-bag. All centres tattoo patients, most using 3-4 tattoos, 1 centre sometimes used surface-guided radiotherapy as an alternative.

Variable verification protocols presented; 6/15 centres perform daily imaging with the others favouring an extended no action level approach. Five centres utilise two different imaging methods, kV-CBCT and 2-dimentional kV imaging were most popular. Five centres use VMAT, 4 TomoTherapy, 3 IMRT, 2 3D-conformal and 1 proton therapy. A wide range in CTV-PTV margins presented (figure 1).

A variety of CSI techniques are being used in the UK. Much can be learnt from sharing practices and expertise. Development of an evidence-based CSI radiotherapy guidance document could support the sharing and unification of good practice.