title: Comparison of different fractionation schedules toward a single fraction in high-dose-rate brachytherapy as monotherapy for low-risk prostate cancer using 3-dimensional radiobiological models.
abstract: OBJECTIVE
  The aim of the present study was the investigation of different fractionation schemes to estimate their clinical impact. For this purpose, widely applied radiobiological models and dosimetric measures were used to associate their results with clinical findings.
  
  
  METHODS
  The dose distributions of 12 clinical high-dose-rate brachytherapy implants for prostate were evaluated in relation to different fractionation schemes. The fractionation schemes compared were: (1) 1 fraction of 20 Gy; (2) 2 fractions of 14 Gy; (3) 3 fractions of 11 Gy; and (4) 4 fractions of 9.5 Gy. The clinical effectiveness of the different fractionation schemes was estimated through the complication-free tumor control probability (P+), the biologically effective uniform dose, and the generalized equivalent uniform dose index.
  
  
  RESULTS
  For the different fractionation schemes, the tumor control probabilities were 98.5% in 1×20 Gy, 98.6% in 2×14 Gy, 97.5% in 3×11 Gy, and 97.8% in 4×9.5 Gy. The corresponding P+ values were 88.8% in 1×20 Gy, 83.9% in 2×14 Gy, 86.0% in 3×11 Gy, and 82.3% in 4×9.5 Gy. With use of the fractionation scheme 4×9.5 Gy as reference, the isoeffective schemes regarding tumor control for 1, 2, and 3 fractions were 1×19.68 Gy, 2×13.75 Gy, and 3×11.05 Gy. The optimum fractionation schemes for 1, 2, 3, and 4 fractions were 1×19.16 Gy with a P+ of 91.8%, 2×13.2 Gy with a P+ of 89.6%, 3×10.6 Gy with a P+ of 88.4%, and 4×9.02 Gy with a P+ of 86.9%.
  
  
  CONCLUSIONS
  Among the fractionation schemes 1×20 Gy, 2×14 Gy, 3×11 Gy, and 4×9.5 Gy, the first scheme was more effective in terms of P+. After performance of a radiobiological optimization, it was shown that a single fraction of 19.2 to 19.7 Gy (average 19.5 Gy) should produce at least the same benefit as that given by the 4×9.5 Gy scheme, and it should reduce the expected total complication probability by approximately 40% to 55%.
authors: Department of Radiation Oncology, University of Texas Health Sciences Center, San Antonio, Texas; Department of Medical Radiation Physics, Karolinska Institutet and Stockholm University, Stockholm, Sweden. Electronic address: mavroidis@uthscsa.edu.
authors: Panayiotis
authors: P
authors: Mavroidis
authors: Department of Medical Physics and Engineering, Strahlenklinik, Klinikum Offenbach GmbH, Offenbach, Germany.
authors: Natasa
authors: N
authors: Milickovic
authors: Department of Radiation Oncology, University of Texas Health Sciences Center, San Antonio, Texas.
authors: Wilbert F
authors: WF
authors: Cruz
authors: Strahlenklinik, Klinikum Offenbach GmbH, Offenbach, Germany.
authors: Nikolaos
authors: N
authors: Tselis
authors: Pi-Medical Ltd., Athens, Greece.
authors: Andreas
authors: A
authors: Karabis
authors: Department of Radiation Oncology, University of Texas Health Sciences Center, San Antonio, Texas.
authors: Sotirios
authors: S
authors: Stathakis
authors: Department of Radiation Oncology, University of Texas Health Sciences Center, San Antonio, Texas.
authors: Nikos
authors: N
authors: Papanikolaou
authors: Strahlenklinik, Klinikum Offenbach GmbH, Offenbach, Germany.
authors: Nikolaos
authors: N
authors: Zamboglou
authors: Department of Medical Physics and Engineering, Strahlenklinik, Klinikum Offenbach GmbH, Offenbach, Germany; Nuclear and Particle Physics Section, Physics Department, University of Athens, Athens, Greece.
authors: Dimos
authors: D
authors: Baltas
mesh_terms: D001918:Brachytherapy / Q000009:adverse effects / Q000379:methods*; D019583:Dose Fractionation, Radiation; D006801:Humans; D008297:Male; D008954:Models, Biological; D058958:Organs at Risk / Q000000981:diagnostic imaging / Q000528:radiation effects; D011336:Probability; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D011832:Radiation Injuries / Q000517:prevention & control*; D012007:Rectum / Q000000981:diagnostic imaging / Q000528:radiation effects; D012016:Reference Values; D012062:Relative Biological Effectiveness; D047368:Tumor Burden; D018084:Ultrasonography, Interventional / Q000379:methods; D014521:Urethra / Q000000981:diagnostic imaging / Q000528:radiation effects; D001743:Urinary Bladder / Q000000981:diagnostic imaging / Q000528:radiation effects