CONFORMAL PROTON THERAPY FOR PROSTATE CARCINOMA

Background: The role and optimum dose of radiation to eradicate prosta te cancer continues to be evaluated. Protons offer an opportunity to i ncrease the radiation dose to the prostate while minimizing treatment toxicity. Methods: Six hundred forty-three patients with localized pro state cancer were treated with protons, with or without photons. Treat ments were planned with a 3D planning system; patients received 74-75 CGE (Cobalt Gray Equivalent) at 1.8-2.0 CGE per fraction. Patients wer e evaluated for response to therapy and treatment-related toxicity. Re sults: The overall clinical disease-free survival rate was 89% at 5 ye ars. When post-treatment prostate-specific antigen (PSA) was used as a n endpoint for disease control, the 4.5-year disease-free survival rat e was 100% for patients with an initial PSA of < 4.0 ng/ml, and 89%, 7 2%, and 53% for patients with initial PSA levels of 4.1-10.0, 10.1-20. 0, and > 20.0, respectively. Patients in whom the post-treatment PSA n adir was below 0.5 ng/ml did significantly better than those whose nad ir values were between 0.51-1.0 or > 1.0 ng/ml: the corresponding 5-ye ar disease-free survival rates were 91%, 79%, and 40%, respectively. M inimal radiation proctitis was seen in 21% of patients; toxicity of gr eater severity was seen in less than 1%. Conclusion: Proton therapy to 74-75 CGE produced minimal treatment-related toxicity and excellent P SA normalization and disease-free survival in patients with low initia l PSA levels. A prospective randomized dose-escalation trial is now un derway to help define the optimum dose of radiation for patients with early stage prostate cancer. (C) 1998 Elsevier Science Inc.