KEY POINTS
- BARitOne is a single-centre R-IDEAL stage 2a–2b study evaluating biologically adaptive radiotherapy in poor-prognosis stage III–IVb oropharyngeal squamous cell carcinoma treated without concurrent systemic therapy.
- Eligible patients have HPV-negative disease or HPV-positive disease with a smoking history of at least 10 pack-years within 20 years of diagnosis. Patients planned for concurrent chemotherapy or cetuximab, those with distant metastases, and low-risk HPV-positive disease are excluded.
- All participants begin standard radiotherapy to 65 Gy in 30 fractions. Diffusion-weighted MRI is performed immediately before fraction one and after fraction ten to measure changes in apparent diffusion coefficient within primary and nodal gross disease.
- Tumours are classified as non-responding when the apparent diffusion coefficient rises by less than 18% in the primary tumour or less than 27% in involved nodes. All other tumours continue standard-dose treatment.
- Non-responders receive 40.5 Gy in 15 fractions to gross disease during fractions 16–30 rather than the standard second-phase dose, producing a cumulative gross-tumour dose of 73 Gy in 30 fractions.
- Planning uses VMAT, 3-mm target margins, and daily online image guidance. A mandatory safety constraint limits the primary-tumour volume receiving more than 84 Gy to no greater than 1.75 cm³, based on previous dose–ulceration modelling.
- The primary endpoint is the proportion of participants completing the diffusion-MRI-guided adaptive pathway. Grade 3 toxicity, patient-reported quality of life, and disease-control outcomes are secondary endpoints; the protocol provides no evidence yet that MRI-selected escalation is safe or improves control.
CLINICAL TAKEAWAY
BARitOne addresses a rational question: whether dose escalation can be restricted to biologically poor responders rather than imposed on every high-risk patient. Its immediate value is workflow and safety development; any effect on local control will require subsequent prospective comparative testing.