Innovative strategies for image-guided proton treatment of prostate cancer

Proton beam therapy has a proven track record of treating non-metastatic prostate cancer with excellent disease-free survival results when using homogeneous doses between 75 and 82 CGE (Cobalt Gray Equivalent) to the prostate target volume. In clinically organ-confined prostate cancer, it may be possible, in principle, to further improve outcomes by reducing the margins of the high-dose planning target volume to the gross tumor volume and by covering the clinical target volume with a dose sufficient to control microscopic extensions of the tumor. This would allow further dose escalation without increasing the risk of acute and late effects. In this paper, we undertake a careful review of existing histopathological data that support this view and discuss technical possibilities to this approach utilizing the highly conformal characteristics of proton beams and combining them with modern 4D imaging and treatment techniques.