OPTIMIZATION OF CONFORMAL RADIATION TREATMENT OF PROSTATE-CANCER - REPORT OF A DOSE-ESCALATION STUDY

Purpose: The development of conformal radiation technique including im proved patient immobilization has allowed us to test the value of dose escalation in optimizing the radiation treatment of prostate cancer. Methods and Materials: Outcome is reported for 233 consecutive patient s treated with conformal technique between March 1989 and October 1992 . Dose was escalated from 68 dy to 79 Gy. Patient status is reported a t 3 years follow-up, which is available in all alive patients. Pretrea tment and serial posttreatment prostate specific antigen (PSA) values are available for all patients. Biochemical freedom of disease (bNED) defines failure as PSA >1.5 ngm/ml and rising on two consecutive measu res. Dose response for bNED control of cancer and late morbidity are r epresented by legit response models fitted to the data. Kaplan-Meier m ethods, the log rank test, and Cox Regression models are also used. Re sults: No dose response is observed for bNED survival for patients wit h pretreatment PSA <10 ngm/ml comparing patients treated above or belo w 71.5 Gy or on multivariate analysis. Dose response is observed for b NED survival for pretreatment PSA groups of 10-19.9 ngm/ml and 20+ ngm /ml. The dose associated with 50% bNED survival at 3 years is 64 Gy an d 76 Gy, respectively. The slope of the dose responses are 13 and 9%, respectively. Dose response is demonstrated for Grade 2 gastrointestin al (GI), Grade 2 genitourinary (GU), and Grade 3,4 combined GI and GU late morbidity. The slopes of the morbidity responses are steeper than for cancer control (19 to 21%). Conclusions: Patients with pretreatme nt PSA <10 ngm/ml do not benefit from dose escalation, and the serious late morbidity of conformal radiation at 70 Gy is <3%. Patients with PSA values 10-19.9 ngm/ml and 20+ ngm/ml benefit from dose escalation beyond 70 Gy. Treatment beyond 75 Gy results in >10% serious morbidity unless special precautions are taken to protect the rectal mucosa. Al l levels of severity of radiation morbidity show a dose response and c ombined with the dose response for bNED survival these data allow the optimization of treatment. (C) 1997 Elsevier Science Inc.