Prostate Motion: Implications and Management Strategies

Further developments in precision and high-dose radiotherapy for patients with prostate cancer demand a greater understanding of prostate motion and the ways it can be managed. Prostate movement can occur unpredictably both between fractions and during fractions of radiotherapy. Nearly 14% of conventional radiotherapy treatments are given when the prostate displacement exceeds the CTV-PTV margin [1]. This chapter discusses the three mechanisms of prostate motion: translational movements, rotational movements, and prostate deformation. We discuss the factors that induce or affect prostate motion, such as rectal movement, as well as ways of detecting and characterizing movement of the prostate with various imaging techniques. Imaging modalities that can detect prostate position prior to radiotherapy are reviewed including CT on rails, TomoTherapy®, fiducials with kV imaging using CyberKnife®, and electromagnetic transponders (Calypso®). Methods of adapting treatment to mitigate these effects are discussed. These include off-line corrections after imaging, online imaging, and correction and adaptive replanning. Conclusions regarding the standard of care for prostate cancer patients are presented, along with avenues for future research.