1 National Radiotherapy Trials Quality Assurance (RTTQA) Group, UK; Mount Vernon Cancer Centre, Northwood, UK. Electronic address: elizabeth.miles@nhs.net.
2 Weston Park Cancer Centre, Sheffield, UK.
3 National Radiotherapy Trials Quality Assurance (RTTQA) Group, UK; Mount Vernon Cancer Centre, Northwood, UK.
4 National Radiotherapy Trials Quality Assurance (RTTQA) Group, UK; South West Wales Cancer Centre, Swansea, UK; Faculty of Medicine, Health and Life Science, Swansea University, Swansea, UK.