The use of CT-MR image registration to define target volumes in pelvic radiotherapy in the presence of bilateral hip replacements

Increasing numbers of patients with hip replacements are presenting for pelvic radiotherapy, which is usually planned using CT images. Image artefacts caused by the presence of metallic implants tend not to be severe for single hip replacements and allow for adequate definition of target volumes. When bilateral hip replacements are present, the image artefacts can render CT images useless for target definition, particularly for tumours of the prostate and bladder. MR images are not susceptible to such severe artefacts. This note describes a small series of patients with bilateral hip replacements on whom CT-MR image registration has been used to successfully define adequate target volumes.