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

To achieve a better correction effect in radiation treatment, a correction (c(alpha)) is suggested which is optimal in the sense of minimal standard deviation of the residual systematic displacement (Delta(r)) obtained after correction. To evaluate the improvement due to c(alpha), the performance of the original Eel's rule [2] was compared to the performance of its modification, where same decision-making thresholds were used but a correction c(alpha) was applied. For this, 5000 treatment courses were simulated at different standard deviations (sigma(Delta) and sigma(delta)) of the systematic displacement Delta and random error delta. The experiments showed improved accuracy by up to 7% in terms of \Delta(r)\ less than or equal to 1.5 mm and also a reduced average number of corrections per patient of about 0.1 corrections. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.