title: Investigating the dosimetric and tumor control consequences of prostate seed loss and migration.
abstract: OBJECTIVE
  Low dose-rate brachytherapy is commonly used to treat prostate cancer. However, once implanted, the seeds are vulnerable to loss and movement. The goal of this work is to investigate the dosimetric and radiobiological effects of the types of seed loss and migration commonly seen in prostate brachytherapy.
  
  
  METHODS
  Five patients were used in this study. For each patient three treatment plans were created using Iodine-125, Palladium-103, and Cesium-131 seeds. The three seeds that were closest to the urethra were identified and modeled as the seeds lost through the urethra. The three seeds closest to the exterior of prostatic capsule were identified and modeled as those lost from the prostate periphery. The seed locations and organ contours were exported from Prowess and used by in-house software to perform the dosimetric and radiobiological evaluation. Seed loss was simulated by simultaneously removing 1, 2, or 3 seeds near the urethra 0, 2, or 4 days after the implant or removing seeds near the exterior of the prostate 14, 21, or 28 days after the implant.
  
  
  RESULTS
  Loss of one, two or three seeds through the urethra results in a D(90) reduction of 2%, 5%, and 7% loss, respectively. Due to delayed loss of peripheral seeds, the dosimetric effects are less severe than for loss through the urethra. However, while the dose reduction is modest for multiple lost seeds, the reduction in tumor control probability was minimal.
  
  
  CONCLUSIONS
  The goal of this work was to investigate the dosimetric and radiobiological effects of the types of seed loss and migration commonly seen in prostate brachytherapy. The results presented show that loss of multiple seeds can cause a substantial reduction of D(90) coverage. However, for the patients in this study the dose reduction was not seen to reduce tumor control probability.
authors: Department of Radiation Oncology, University of Texas Health Science Center at San Antonio, San Antonio, TX 78229, USA. knaup@livemail.uthscsa.edu
authors: Courtney
authors: C
authors: Knaup
authors: Panayiotis
authors: P
authors: Mavroidis
authors: Carlos
authors: C
authors: Esquivel
authors: Sotirios
authors: S
authors: Stathakis
authors: Gregory
authors: G
authors: Swanson
authors: Dimos
authors: D
authors: Baltas
authors: Nikos
authors: N
authors: Papanikolaou
mesh_terms: D001918:Brachytherapy / Q000379:methods*; D006801:Humans; D008297:Male; D009038:Motion; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011874:Radiometry; D013997:Time Factors; D016896:Treatment Outcome