A Randomized Trial of High and Low Source Strength I-125 Prostate Seed Implants

Reviewer: Neha Vapiwala, MD
Abramson Cancer Center of the University of Pennsylvania
Ultima Vez Modificado: 22 de octubre del 2003

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Presenter: Vrinda Narayana, MD
Presenter's Affiliation: University of Michigan
Type of Session: Scientific

Background

    Prostate brachytherapy is an established treatment modality for early, localized adenocarcinoma of the prostate. Selected patients with low-risk features based on clinical stage, Gleason score, and serum PSA level can undergo permanent prostate seed implantation as an alternative to radical prostatectomy or external beam radiation. The preferred seed isotope for permanent implants is I-125, but a range of source activities (0.3-1.3 U or 0.25-1 mCi) can be used, as no consensus exists on this matter. This study sought to compare high and low strength I-125 seed strengths from the perspective of implant quality, cost, and toxicity. The investigators' hypothesis was that no difference would be demonstrated between the two groups.

Materials and Methods

  • 40 patients randomized to receive either:
    1. high seed strength (0.76 U, ~0.6 mCi) implant
    2. low seed strength (0.4 U, ~0.3 mCi) implant
  • Treatment population was a mix of patients undergoing primary brachytherapy treatment (n=10) and patients receiving boost treatment (n=30)
  • The primary and boost patients were comparably matched in both arms.
  • Primary tx pts were treated to 145 Gy while boost tx pts were treated to 108 Gy
  • Patients were all implanted by the same team
  • Ultrasound-guided image planning in the OR using Variseed software and I-125 rapid strands; seed drop-off monitored with fluoroscopy
  • Average prostate gland size = 40 cc
  • Average number of seeds: high = 60 +/-16; low = 96 +/-13
  • Post-implant dosimetric evaluation about 15 days later using CT scan and T2-weighted MRI images, the latter considered more precise than the former
  • CT dosimetry: source positions obtained by autorecognition on 2-mm slices.
  • MRI dosimetry: CT and MRI images registered using mutual information, MRI dosimetry derived from CT source positions.
  • Endpoints of interest included the following implant quality parameters:
    1. dose index, defined as the ratio of achieved dose to planned dose for CT and MRI as a measure of relative error tolerance; used to avoid inter-patient bias
    2. volume receiving prescribed dose (V100)
    3. cost of source and OR time
    4. acute toxicity based on obstructive/irritative symptom score

Results

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