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UK Photon Radiotherapy Practice for Oligodendroglioma -Data From the Analysis of Proton vs Photon Radiotherapy in
J Golten1, A Bruce2, D Egleston2
1Velindre University NHS Trust, Cardiff, CF14 2TL, UK; Cardiff University, School of Medicine, Cardiff, CF14 4YS, UK.
Aims:
The APPROACH (Analysis of Proton vs Photon Radiotherapy in Oligodendroglioma and Assessment of Cognitive Health) trial is a UK randomised controlled study comparing photon radiotherapy (RT) with proton beam therapy (PBT) for oligodendroglioma, with a primary endpoint of neurocognitive function at five years. As part of the trial's radiotherapy quality assurance (RTQA) programme, a national preaccrual facility questionnaire (FQ) was undertaken to evaluate RT practices across England and Wales and assess readiness for protocol compliance. This study reports UK photon radiotherapy practice for oligodendroglioma and evaluates consistency relative to the APPROACH protocol requirements.
Materials And Methods:
Between December 2022 and September 2025, photon radiotherapy centres in England and Wales (n = 23) and both UK proton centres completed the FQ. The questionnaire captured routine practice in immobilisation, imaging, contouring, planning, and verification. Responses were collated by the National Radiotherapy Trials Quality Assurance (RTTQA) group.
Results:
All centres routinely used thermoplastic mask immobilisation and delivered photon radiotherapy using intensity-modulated radiation therapy/volumetric modulated arc therapy (IMRT/VMAT). Dose schedules were consistent, most commonly 54 Gy in 28-30 fractions for World Health Organization (WHO) grade 2 oligodendroglioma and 59.4 Gy in 33 fractions for grade 3.However, substantial variation was identified in pretreatment imaging: Computed tomography (CT) slice thickness ranged from 1 to 3 mm and magnetic resonance imaging (MRI) T1 slice thickness from 0.8 to 3 mm, with nine centres exceeding the protocol-required 1 mm slice thickness. MRI type and sequencing were inconsistently reported, and not all centres used dedicated planning MRI scans. Marked variability was also observed in organ-at-risk (OAR) contouring. While optic pathway structures and the brainstem were routinely delineated, only 4/23 (17%) centres contoured the hippocampi, and none contoured the hypothalamus as part of standard practice. Auto-contouring tools were used by 65% of centres.
Conclusion:
The findings indicate broad alignment in technique and dose delivery but highlight variability in imaging and OAR delineation. The implementation of the APPROACH trial and associated RTQA processes is hoped to promote national standards in oligodendroglioma RT practice.
