Kilovoltage volumetric imaging in the treatment room.

Flat-panel cone beam CT is maturing to a stable imaging modality. Applications are being developed for radiotherapy, volumetric diagnostic scanning, rotational angiography and mobile C-arm technologies with soft tissue imaging capabilities. Volumetric image-guided radiotherapy is technologically feasible, and has been proven clinically useful with cone beam CT, CT on rails and tomotherapy design configurations. Soft-tissue-based guidance of field placement is now possible for many sites. Evaluation of the relative merits of these technologies requires that the objective of imaging be well defined. Relevant questions include: Can the target or normal structure of interest be localized with the desired precision and accuracy? Can the patient's position be adjusted based on this information within the time constraints of the clinical workload? We must be prepared to compromise diverse clinical objectives and technical features in order to achieve systems with defined and useful functionality. These imaging technologies will lead to a better understanding of the weaknesses, and provide opportunity to reduce errors and improve technical execution of radiotherapy delivery.