Sci‐Fri AM General‐05: Measurement of daily interfraction prostate motion with tomotherapy MVCT images

Abstract

It is well known that the interfraction motion of the prostate gland can have a significant impact on the efficacy of radiotherapy in the treatment of prostate cancer. As we move towards more complex treatment protocols involving dose escalation and adaptive therapy, accurate daily prostate localization will increase in importance. In this work, the daily interfraction prostate motion has been measured for research patients receiving prostate treatment on the Cross Cancer Institute's TomoTherapy Hi*Art unit. An automated rigid registration algorithm designed to overlay the rigid bony anatomy was used to align the daily on‐line MVCT images with their respective planning CT images. The position of the prostate in the MVCT images was achieved using a prostate localization algorithm based on mutual information registration that only requires prostate delineation on the planning CT image. A multi‐start optimization approach was employed to reduce registration uncertainty and eliminate any gross miss‐registrations. The technique was validated with kVCT and MVCT images of two patients with localization seeds implanted in their prostates. Accurate convergence could only be achieved when assuming translations only, thus neglecting any prostate rotation. The maximum interfraction motion observed in the anterior‐posterior, superior‐inferior, and lateral directions was 5.7mm, 5.2mm, and 2.0mm, respectively. Mean and standard deviation values were −1.1mm, 0.4mm, and 0.3mm, and 1.7mm, 2.4mm, and 0.7mm, respectively.