Evaluation of the validity of a convolution method for incorporating tumour movement and set-up variations into the radiotherapy treatment planning system.

Modern radiotherapy techniques have developed to a point where the ability to conform to a particular tumour shape is limited by organ motion and set-up variations. The result is that dose distributions displayed by treatment planning systems based on static beam modelling are not representative of the dose received by the patient during a fractionated course of radiotherapy. The convolution-based method to account for these variations in radiation treatment planning systems has been suggested in previous work. The validity of the convolution method is tested by comparing the dose distribution obtained from this convolution method with the dose distribution obtained by summing the contribution to the total dose from each fraction of a fractionated treatment (for increasing numbers of fractions) and simulating random target position variations between fractions. For larger numbers of fractions (approximately or > 15) which are the norm for radical treatment schemes, it is clear that incorporation of movement by a convolution method could potentially produce a more accurate dose distribution. There are some limitations that have been identified, however, especially in relation to the heterogeneous nature of patient tissues, which require further investigation before the technique could be applied clinically.