Pre-plan parameters predict post-implant D 90 ≥ 140 Gy for 125 I permanent prostate implants

Abstract

PurposeTo find permanent prostate implant (PPI) pre-plan dosimetric parameters that predict post-implant D90 ≥ 140 Gy.Material and methodsPre-plans were evaluated for 504 patients undergoing PPI with 125I 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).Results20% 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.ConclusionsHigher occupancy proportion and larger margins anteriorly and reduced occupancy proportion, and smaller margins posteriorly on PPI pre-plans predict post-implant D90 ≥ 140 Gy.

Stratification of brachytherapy-treated intermediate-risk prostate cancer patients into favorable and unfavorable cohorts

“…Pre-planning technique, intraoperative approach, and dosimetric evaluation have previously been described in detail [ 13 , 14 ]. The brachytherapy target volume consisted of the prostate gland with a 5 mm periprostatic margins and the proximal 1.0 cm of the seminal vesicles with a resultant planning target volume of approximately 1.9 times the actual prostate volume [ 13 , 14 , 15 ]. All post-implant dosimetric calculations were based on day 0 evaluation.…”

The impact of body mass index on dosimetric quality in low-dose-rate prostate brachytherapy

“…Although a D 90 > 130 Gy is considered adequate by the American Brachytherapy Society [8], various studies have shown that a D 90 ≥ 140 Gy is associated with improved biochemical control [9, 10]. Previous studies have found that specific factors such as prostate volume, post-implant prostatic edema, and the number of seeds implanted can influence D 90 [11, 12, 13]. …”