Manual CBCT registration by Japanese radiological technologists: agreement with a clinical reference position and exploratory associations with professional experience

In this retrospective observer study, nine Japanese radiological technologists each performed fully manual offline cone-beam CT registration for 29 cases (261 registrations), blinded to the clinical reference positions adopted by radiation oncologists. Agreement was assessed by three-dimensional deviation; observer-level standard deviation across cases represented between-case variability. Associations with radiotherapy and overall professional experience were explored using Spearman correlations with exact permutation tests and leave-one-observer-out analyses. Mean deviation was 1.41 ± 1.16 mm (median, 1.06 mm); 74.7% of registrations were within 2 mm. Radiotherapy experience was negatively associated with observer-level mean deviation (ρ = -0.820, p = 0.010), but its association with between-case variability was weaker (ρ = -0.502, p = 0.171). Overall professional experience was negatively associated with both outcomes (ρ = -0.895, p = 0.002; ρ = -0.929, p < 0.001). These exploratory associations do not establish independent or causal effects.