Abstracts Archive

UK & Ireland Prostate Brachytherapy Conference 2011

Abstract number 4

Prostate Seed Brachytherapy – Can Ultrasound be used in Post Implant Dosimetry Analysis?

Christopher Walker, St. Luke’s Radiation Oncology Network, Dublin.
Anysja Zuchora, University College Hospital, Galway
Frank Sullivan, University College Hospital, Galway
Margaret Moore. University College Hospital, Galway

Aims/Introduction: AAPM recommendations (Nath et al. Med Phys. 2009 Nov;36(11):5310-22) state that post implant dosimetry of I-125 prostate seed brachytherapy be performed via CT guidance 30 ± 7 days after the procedure. This study attempts to determine whether TRUS based post-implant dosimetry parameters, determined on the day of the case, can be considered statistically equivalent to those acquired from a CT scan taken after 30 days.

Materials/Methods: A retrospective study was performed, visually marking seeds on post-implant TRUS images for 43 patients using Varians Variseed™ software. Dosimetric parameters of D90, V100, and V150 for the prostate were determined for both TRUS and CT. A Paired Students T-Test and a Wilcoxon Paired Sample test were used to determine whether parameters based on these modalities could be considered statistically equivalent. Reproducibility tests were also carried out on the precision of the Variseed seed-finding software.

Results: Analysis showed that TRUS and CT D90 and V100 values could be considered statistically equivalent based on a significance level of 0.05, but V150 could not. For one patient, 100 iterations of the seed finder software on a post-implant CT image set yielded an average prostate D90 of (169.9 ± 2.2)Gy and V100 of (93.5 ± 0.7)%.

Conclusion: The dosimetry parameters of D90 and V100 taken from a post-implant TRUS can be considered statistically equivalent to day-30 CT, however the V150 value cannot. This method has merit especially when natural gland motion occurs during the implant process or if artificial hips are present. The use of multiple iterations of the seed-finder on CT images is also suggested.