Newer Imaging Modalities to Assist With Target Localization in the Radiation Treatment of Prostate Cancer and Possible Lymph Node Metastases

Precise localization of prostate cancer and the drainage lymph nodes is mandatory to define an accurate clinical target volume for conformal radiotherapy. Better target definition and delineation on a daily basis is surely important in quality assurance for fractionated radiation therapy. This article reviews the evidence for major emerging techniques that show promise in better identifying the clinical target volume. Partial prostate boost by brachytherapy, intensity-modulated radiation therapy, or protons has become possible not only with standard imaging techniques but also with the availability of metabolic images obtained by magnetic resonance spectroscopy. Even though fluorine-18 fluorodeoxyglucose (18F-FDG) positron emission tomography has not been found to be useful, novel radiolabeled tracers may eventually prove of value in the diagnosis and treatment planning of prostate cancer. For the metastatic lymph nodes, lymphotropic nanoparticle-enhanced magnetic resonance imaging using ultra-small superparamagnetic iron oxide particles has greater accuracy as compared with conventional techniques and has been instrumental in delineating the lymphatic drainage of the prostate gland. These novel investigational techniques could further help in optimizing conformal radiotherapy for patients with prostate cancer. The concepts of biologic target volume, real target volume, and multidimensional conformal radiotherapy are being explored.