title: Pre-plan parameters predict post-implant D90 ≥ 140 Gy for (125)I permanent prostate implants.
abstract: OBJECTIVE
  To find permanent prostate implant (PPI) pre-plan dosimetric parameters that predict post-implant D90 ≥ 140 Gy.
  
  
  METHODS
  Pre-plans were evaluated for 504 patients undergoing PPI with (125)I seeds for low or intermediate risk prostate cancer. Baseline patient and disease factors, numbers of seeds, ratios of number of seeds to available positions (occupancy proportion), and distances between the 100% isodose line and edge of the prostate (margin) planned for the whole prostate (WP), superior (S), inferior (I), anterior (A), and posterior (P) halves, SA, SP, IA, and IP quarters, and superior (ST), inferior (IT), and middle (MT) thirds, and anterior (AT) and posterior (PT) middle one-sixth segments were analyzed by post-implant D90 subset (≥ 140 Gy vs. < 140 Gy).
  
  
  RESULTS
  20% had post-implant D90 < 140 Gy (mean: 128.0 Gy, range: 97.5-139.2) vs. ≥ 140 Gy (mean: 154.4 Gy, range: 140.0-193.5). The D90 ≥ 140 Gy subset had larger AT and IA segment mean numbers of seeds (p = 0.01, 0.046), larger WP, S, A, SA, ST, AT, and MT segment mean margins (p = 0.01, 0.01, 0.001, 0.0001, 0.03, 0.005, 0.02), and lower PT segment occupancy proportion (p = 0.004). On multivariate analysis, independent predictors of post-implant D90 ≥ 140 Gy were increased SA mean margin, no pre-implant 5-α-reductase inhibitor, higher pre-plan D90, decreased P occupancy proportion, no pre-implant hormone therapy, and decreased SP mean margin.
  
  
  CONCLUSIONS
  Higher occupancy proportion and larger margins anteriorly and reduced occupancy proportion, and smaller margins posteriorly on PPI pre-plans predict post-implant D90 ≥ 140 Gy.
authors.affiliation: Department of Radiation Oncology, University of California, San Francisco Helen Diller Family Comprehensive Cancer Center, San Francisco, California, USA.
authors.forename: Jes
authors.initials: J
authors.lastname: Alexander
authors.affiliation: Biostatistics Core, University of California, San Francisco Helen Diller Family Comprehensive Cancer Center, San Francisco, California, USA.
authors.forename: Vivian
authors.initials: V
authors.lastname: Weinberg
authors.affiliation: Department of Radiation Oncology, University of California, San Francisco Helen Diller Family Comprehensive Cancer Center, San Francisco, California, USA.
authors.forename: Alexander R
authors.initials: AR
authors.lastname: Gottschalk
authors.affiliation: Department of Radiation Oncology, University of California, San Francisco Helen Diller Family Comprehensive Cancer Center, San Francisco, California, USA.
authors.forename: I-Chow Joe
authors.initials: IC
authors.lastname: Hsu
authors.affiliation: Department of Urology, University of California, San Francisco Helen Diller Family Comprehensive Cancer Center, San Francisco, California, USA.
authors.forename: Katsuto
authors.initials: K
authors.lastname: Shinohara
authors.affiliation: Department of Radiation Oncology, University of California, San Francisco Helen Diller Family Comprehensive Cancer Center, San Francisco, California, USA.
authors.forename: Mack
authors.initials: M
authors.lastname: Roach
keywords: LDR brachytherapy; pre-plan dosimetry; prostate cancer
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