Image-guided radiotherapy strategies in upper gastrointestinal malignancies.

Organ motion due to breathing, peristalsis and deformation presents challenging problems for the delivery of highly conformal radiotherapy to upper abdominal targets, despite the many advancements in the technology of radiation planning and delivery. It is important to understand and account for this motion to avoid treatment inaccuracies, especially systematic errors that could potentially impact the probability of tumor control or increase the risk of normal tissue toxicity. Various image guidance tools can be utilized from the outset of radiation planning through treatment to minimize introducing such errors. These strategies include: assessment of breathing motion (with or without breath hold) prior to simulation, 4D CT simulation and cine MRI to evaluate tumor/organ motion, and image guidance on the treatment unit using kV fluoroscopy and 4D cone-beam CT. Together, image guidance methods can provide greater assurance that concordance exists between planned and delivered doses during a course of radiotherapy.