Image-guided radiotherapy for localized prostate cancer: treating a moving target.

Prostate motion during external-beam radiotherapy can affect outcomes in patients with localized prostate cancer. Prostate motion and deformation are currently being characterized with different techniques. There is significant individual variation among patients with respect to the observed motion and its dosimetric consequences. There is also significant difference in the accuracy of different localization methods currently used to adjust for prostate motion. The motion of the prostate gland can itself affect the accuracy of different localization methods. The dosimetric impact on target areas and organs at risk should be studied for different localization techniques, treatment plan margins, and treatment schedules. Such assessments will be increasingly important with smaller treatment margins, smaller fraction numbers, and higher radiation doses. Understanding and managing the consequences of anatomic variations within the lower pelvis should be a priority in designing and implementing future clinical trials.