Probability of seminal vesicle involvement in localized prostatic carcinoma. Significance in conformal radiotherapy

PURPOSE: The development of objective criteria for selecting patients for seminal vesicle irradiation on radical radiotherapy for prostate cancer will be important for successful planning of 3D conformal radiotherapy. MATERIALS AND METHODS: Based on morphometric studies from radical prostatectomy specimens, new imaging modalities with potential in the investigation of patients with gross seminal vesicle involvement and clinical factors with potential in the identification of patients with subclinical disease the development of objective guidelines is possible. RESULTS: Clinical tumor stage as determined by digital rectal examination, diagnostic tumor biopsy (Gleason Score), and pretherapy serum prostate-specific antigen value were significant factors for the probability of involvement of seminal vesicles. Studies show that seminal vesicle involvement is unlikely if the PSA is < 4 ng/ml or 4 to 10 ng/ml and Gleason Score < 7 and stage < or = T2b. In contrast, involvement of seminal vesicles is highly likely with levels above 20 ng/ml. In patients with PSA levels between 10 and 20 ng/ml and Gleason Score < 7 ultrasonographic findings with regard to tumor volume and localization will be useful to determine the extent of the target volume. For treatment planning a significant reduction in the volumes of irradiation to the rectum and bladder is evident when seminal vesicles were excluded. CONCLUSION: Prospective use of the objective criteria will be useful in the selection of patients for seminal vesicle involvement and should be an integral part in 3D conformal radiotherapy of prostate cancer.