The magnitude of treatment field set-up parameter correction in radiation therapy

To achieve a better correction effect in radiation treatment, a correction ( c α ) is suggested which is optimal in the sense of minimal standard deviation of the residual systematic displacement ( Δ r) obtained after correction. To evaluate the improvement due to c α , the performance of the original Bel's rule [2]was compared to the performance of its modification, where same decision-making thresholds were used but a correction c α was applied. For this, 5000 treatment courses were simulated at different standard deviations ( σ Δ and σ δ ) of the systematic displacement Δ and random error δ. The experiments showed improved accuracy by up to 7% in terms of | Δ r|≤1.5 mm and also a reduced average number of corrections per patient of about 0.1 corrections.