Background: A randomised study to investigate whether bilateral arm abduction is superior to unilateral abduction with respect to stability using shifts on treatment as the main outcome measure.
Material and Methods: 50 consecutive female patients were randomised to ipsilateral or bilateral arm abduction. Central lung depth (CLD) and cranial caudal depth (CCD) on the simulator image was compared with that featured on three Electronic Portal Images (EPI) captured during treatment for each patient. Systematic and random errors were analysed with respect to the average translational displacement and standard deviation per patient and per population between the planning image and the EPI.
Results: The CLD average translational displacement in the test group was −1.7 mm (95% CI = −5 to 1.6 mm) Σ pop = 2.3 mm, σ pop = 1.6 mm, and in the control group −1.9 mm (95% CI = −6 to 3 mm) Σ pop = 4 mm, σ pop = 2.1 mm. The average translational displacement of CCD in test group was 0 mm (95% CI = − 5.3 to 5.1 mm) Σ pop = 2.2 mm, σ pop = 2.6 mm. CCD translational displacement was greater in the unilateral arm abduction group at − 1.6 mm (95% CI = −6.7 to 3.4 mm) Σ pop = 3.6 mm, σ pop = 2.4mm.
Conclusion: The reduction in systematic error and inter-patient variability observed in the test group is evidence that bilateral arm abduction is a more stable and reproducible position than unilateral arm abduction. The CCD translational data indicates that patients treated with unilateral arm abduction were moving inferiorly on the breast board. These results support the adoption of bilateral arm abduction as a standard technique.