AbstractID: 7052 Title: Dosimetric Study of Seed Activities in Permanent Prostate Implants
with Pd-103
Our permanent prostate brachytherapy philosophy is to treat the planning target volume with a conformal,
individualized plan, requiring the use of many needles. We have previously shown, however, that an
increasing number of needles predicts an increased risk of acute urinary retention after implantation (Int J
Radiat Oncol Biol Phys 48:1457-1460; 2000). The purpose of this study is to evaluate the ability to decrease
the number of needles by increasing the activity of the individual seeds and the dosimetric impact of this
strategy on normal tissues. Twenty prostate cancer patients treated with permanent 103Pd implant were
studied. Treatment plans were generated with different 103Pd seed activities ranging from 1.8 mCi to 2.4 mCi.
Plans were initially created by the VariSeed™ (Varian Corp., Palo Alto, CA) optimization program and then
modified slightly as needed. We attempted to cover the entire PTV with prescribed dose 140Gy, 85% of the
PTV with 125%, 60% with 150%, 30% with 200% and limit the dose to the neurovascular bundles and
urethra to less than 100% and 150%, respectively. The following factors were analyzed: number of needles,
number of seeds, target-volume ratio (TVR), and dosimetric coverage of the PTV (V100, V125, V150,
V200), urethra (V100, V150), and neurovascular bundles (V50, V75, V100). We have found that increased
103
Pd seed activity in permanent prostate implants from results in plans with a decreased number of needles
and seeds, potentially resulting in less trauma to the prostate, without significantly compromising urethral and
neurovascular bundle sparing.