Prediction of Effectiveness of 3D Conformal External Beam Radiation Therapy
Kattan is a very prolific researcher and has developed many nomograms for use in many different cancers, including many dealing with prostate cancer. Nomogram 5 was created for predicting the probability that a patient will develop metastasis within five years after three-dimensional conformal radiation therapy (3DCRT) to the prostate.5
Kattan’s group conducted a retrospective, nonrandomized analysis of 1,677 patients treated with three-dimensional CRT at Memorial Sloan-Kettering Cancer Center (MSKCC) from 1988 to 2000. Clinical parameters examined were pretreatment PSA level, clinical stage, and biopsy Gleason score. Patients were followed until their deaths, and the time at which they developed metastasis was noted. A nomogram for predicting the five-year probability of developing metastasis was constructed from the MSKCC cohort and was validated using a Cleveland Clinic series of 1,626 patients.
After three-dimensional CRT, 159 patients developed metastasis. At five years, 11% of patients experienced metastasis. A nomogram constructed from the data gathered from these men showed an excellent ability to discriminate among patients in an external validation data set, as shown by a concordance index of 0.81. Hence, Kattan concluded that his nomogram had reasonable accuracy and discrimination.
Nomogram 5 is useful (1) in counseling patients who are candidates for external beam radiation before therapy and (2) in selecting patients for prospective clinical trials. Using this nomogram, the physician can give a reasonably accurate prediction of the probability that a patient will develop metastasis within five years after receiving primary three-dimensional conformal radiation therapy. This is a more clinically useful end point than biochemical recurrence because a large proportion of PSA-only recurrence (biochemical recurrence) patients will not have any further disease progression.
Clinical scenario 5: Using Nomogram 5, a patient with a PSA of 12 ng/ml (20 points), with clinical stage T2B (33 points), Gleason’s score 4+3 = 7 (15 points) has a total of 68 points. This patient has an 8% risk of having metastatic disease five years following definitive 3D conformal XRT as primary therapy.
5. Kattan MW, Zelefsky MJ, Kupelian PA, et al: Pretreatment Nomogram That Predicts 5-Year Probability of Metastasis Following Three-Dimensional Conformal Radiation Therapy for Localized Prostate Cancer. Journal of Clinical Oncology, Vol 21, 4568-4571, 2003.