Daily isocenter correction with electromagnetic-based localization improves target coverage and rectal sparing during prostate radiotherapy.

Purpose: To evaluate dosimetric consequences of daily isocenter correction during prostate cancer radiation therapy using the Calypso 4D localization system.

Methods And Materials: Data were analyzed from 28 patients with electromagnetic transponders implanted in their prostates for daily target localization and tracking. Treatment planning isocenters were recorded based on the values of the vertical, longitudinal, and lateral axes.