Multi-model verification of patient positioning in radiotherapy

Conformal radiotherapy uses multi-leaf collimation to customise radiation dose fields to the three-dimensional shape of the target tumour. Its effectiveness is governed by the precision of dose delivery achieved using a few coplanar tattoo markers. During a course of treatment, the patient's body surface profile fluctuates causing the reference skin tattoo markers to move and hence, without the ability to verify target position, the precision of pretreatment set-ups will degrade, often significantly. Cross-modal patient set-up verification software has been developed which allows the user to examine images from various modalities. All imaging modalities available can be used to collectively define anatomical landmarks, outlined on a representative reference image in order to verify radiation field placement using anterior and lateral pre-treatment portal images. This software is presently being used within a national clinical trial for recording the field placement error observed daily at pre-treatment.