Comparing GTV Delineation With and Without Spatially Registered Endoscopy

The last decade has seen progressive advances in RT delivery, such as intensity modulated radiation therapy (IMRT)and image-guided radiation therapy (IGRT), which now allow highly precise radiation dose delivery. Together, IMRT and IGRT offer the potential of more selective treatment of the primary tumour and surrounding neck nodes by reducing the dose inflicted on critical organs at risk without compromising tumour dose and. IMRT has been shown to significantly decrease radiation-induced toxicity, and is now considered standard treatment for H&N tumors. With these advances in delivery technology, the accurate definition of the target is emerging as the weakest link in the radiotherapeutic treatment chain. Accurate target definition is the primary link on which all subsequent treatment planning and delivery depend and is therefore critical for successful RT. Incorrect target definition can result in poorer outcomes through either less tumour control, more normal tissue toxicity, or both. Computed x-ray tomography (CT) is the standard volumetric imaging modality for RT because of its high resolution, accurate definition of anatomy and its intrinsic measure of electron density necessary for accurate dose calculation. However, its ability to distinguish between tumour and normal tissue is limited due to a lack of contrast for structures of similar electron density and image artifacts for objects of high density. This additional noise can result in large inter-observation variability. Disease visible on endoscopy can be contoured and registered to the planning CT, allowing inclusion of superficial disease invisible on the volumetric CT image dataset into the treatment plan.