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 pre-treatment 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.