PET/CT and radiotherapy in prostate cancer

Radiotherapy is one of the corner stone treatments for patients with prostate cancer. Especially for locally advanced tumors radiotherapy +/- adjuvant androgen deprivation treatment is standard of care. This brings up the need for accurate assessment of extra prostatic tumor growth and/or the presence of nodal metastases for selection of the optimal radiation dose and treatment volume. Morphological imaging like transrectal ultra sound, computed tomography (CT) and magnetic resonance imaging (MRI) are routinely used but are limited in their accuracy in detecting extra prostatic extension and nodal metastases. In this article we present a structured review of the literature on positron emission tomography (PET)/CT and radiotherapy in prostate cancer patients with emphasis on: 1) the pretreatment assessment of extra prostatic tumor extension, nodal and distant metastases; 2) the intraprostatic tumor characterization and radiotherapy treatment planning; and 3) treatment evaluation and the use of PET/CT in guidance of salvage treatment. PET/CT is not an appropriate imaging technique for accurate T-staging of prostate cancer prior to radiotherapy. Although macroscopic disease beyond the prostatic capsule and into the periprostatic fat or in seminal vesicle is often accurately detected, the microscopic extension of prostate cancer remains undetected. Choline PET/CT holds a great potential as a single step diagnostic procedure of lymph nodes and skeleton, which could facilitate radiotherapy treatment planning. At present the use of PET/CT for treatment planning in radiotherapy is still experimental. Choline PET based tumor delineation is not yet standardized and different segmentation-algorithms are under study. However, dose escalation using dose-painting is feasible with only limited increases of the doses to the bladder and rectum wall. PET/CT using either acetate or choline is able to detect recurrent prostate cancer after radiotherapy but stratification of patients for any local salvage treatment has not been addressed in the current literature.