title: The durability of external beam radiation therapy for prostate cancer: can it be identified?
abstract: OBJECTIVE
  We establish criteria to identify a durable response to external beam radiation therapy by calculation of biochemical progression-free probability for patients who attained and maintained defined nadir prostate specific antigen (PSA) levels more than 5 years after treatment.
  
  
  METHODS
  A total of 460 patients were treated with external beam radiation monotherapy from 1976 to 1995. Patients with PSA less than 0.5 (group 1) or 0.5 to 1.0 (group 2) ng./ml. more than 5 years after treatment were identified. Treatment failure was defined as 3 consecutive increases in PSA after nadir. Progression-free probability after 60 months was calculated for each group. A comparison was also made to patients achieving the same nadir levels anytime after treatment.
  
  
  RESULTS
  Failure occurred at 133 months in 1 of 26 group 1 patients (4%) and at a median of 76 months in 5 of 26 group 2 patients (19%). At 10 years progression-free probability was 91% for group 1 compared to 72% for group 2 (p = 0.0575). These same nadir levels anytime after treatment were associated with higher failure rates of 55% for group 1 and 72% for group 2.
  
  
  CONCLUSIONS
  If a PSA nadir of less than 0.5 ng./ml. was maintained 5 years after therapy, subsequent failure was rare. Although statistical significance was not reached (p = 0.0575), a higher failure rate was noted if the nadir PSA was 0.5 to 1.0 ng./ml. at 5 years. Thus, patients with PSA 0.5 to 1.0 ng./ml. require careful continued surveillance. Nadir levels less than 1.0 ng./ml. anytime before 5 years were associated with a substantial risk of subsequent progression.
authors.affiliation: Department of Urology, Eastern Virginia Medical School, Virginia Prostate Center, Norfolk, USA.
authors.forename: J W
authors.initials: JW
authors.lastname: Davis
authors.forename: P
authors.initials: P
authors.lastname: Kolm
authors.forename: G L
authors.initials: GL
authors.lastname: Wright
authors.forename: D
authors.initials: D
authors.lastname: Kuban
authors.forename: A
authors.initials: A
authors.lastname: El-Mahdi
authors.forename: P F
authors.initials: PF
authors.lastname: Schellhammer
mesh_terms: D018450:Disease Progression; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D017430:Prostate-Specific Antigen / Q000097:blood; D011471:Prostatic Neoplasms / Q000097:blood / Q000532:radiotherapy*; D013997:Time Factors
chemical_list: D017430:Prostate-Specific Antigen