Loose Seeds Vs. Stranded Seeds: A Comparison Of Critical Organ Dosimetry And Acute Toxicity In (125)I Permanent Implant For Low-Risk Prostate Cancer

Main Category: Prostate / Prostate Cancer
Also Included In: Urology / Nephrology
Article Date: 30 May 2008 - 0:00 PDT

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UroToday.com - The prostate brachytherapy program at Princess Margaret Hospital began in March 1999 and has treated over 1000 patients. In September 2000 we began using MR-CT fusion for all postplan evaluations. The improved soft tissue definition of MR imaging provided insight into issues of implant quality and post implant edema not readily perceived with routine use of CT imaging alone.

The first of the 2 cohorts described in this paper was implanted with loose seeds and imaged with MR and CT on days 0, 7 and 30 to study the extent of post implant edema and its resolution over time1. The second cohort was implanted with a custom-stranded seed product and imaged in the same fashion with MR-CT fusion on days 0, 7 and 30, with the primary intent of looking at strand stability over time and the effect of strands on prostate edema2.

The current article is a spin-off from these 2 data sets. It was not the primary intent of these studies to compare dosimetry of the urethra and rectal wall for loose seed implants vs. stranded seed implants; in fact no difference was expected to be found between loose seeds and stranded seeds in this respect. However, once discovered, the finding of a difference in dose to these structures required explanation and clinical perspective.

The slightly higher urethral dose seen in the stranded cohort may be due to the fact that less edema was seen at all time points with strands (p-value: ns) but this slightly higher urethral dose is probably of no clinical significance.

The increased rectal dose seen with strands is of more concern but is certainly not a condemnation of strands or a reason to avoid their use. It may simply be an indication that optimal implant technique for strands may be slightly different than that for loose seeds. Practitioners who use both loose seeds and strands should be aware of these differences. Attention to rectal dose as part of the postplan quality assessment with consistent evaluation of RV100 (volume of rectal wall receiving 100% of the prescribed dose) will allow any required technical modifications to be rapidly implemented and permit high quality implants to be obtained with either seed format.

References:

1.Taussky D, Austen L, Toi A, et al. Sequential evaluation of prostate edema after permanent seed prostate brachytherapy using CT-MRI fusion. Int J Radiat Oncol Biol Phys 2005;62:974-980.

2. Saibishkumar EP, Borg J, Yeung I et al. A sequential comparison of seed loss and prostate dosimetry of stranded seeds with loose seeds in 125I permanent implant for low risk prostate cancer. Int J Radiat Oncol Biol Phys in press

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