title: Impact of edema and seed movement on the dosimetry of prostate seed implants.
abstract: This article summarizes current knowledge concerning the characterization of prostatic edema and intra-prostatic seed movement as these relate to dosimetry of permanent prostate implants, and reports the initial application to clinical data of a new edema model used in calculating pre- and post-implant dose distributions. Published edema magnitude and half-life parameters span a broad range depending on implant technique and measurement uncertainty, hence clinically applicable values should be determined locally. Observed intra-prostatic seed movements appear to be associated with particular aspects of implant technique and could be minimized by technique modification. Using an extended AAPM TG-43 formalism incorporating the new edema model, relative dose error RE associated with neglecting edema was calculated for three I-125 seed implants (18.9 cc, 37.6 cc, 60.2 cc) performed at our center. Pre- and post-plan RE average values and ranges in a 50 × 50 × 50 mm(3) calculation volume were similar at ~2% and ~0-3.5%, respectively, for all three implants; however, the spatial distribution of RE varied for different seed configurations. Post-plan values of D90 and V100 for prostate were reduced by ~2% and ~1%, respectively. In cases where RE is not clinically negligible as a consequence of large edema magnitude and / or use of Pd-103 seeds, the dose calculation method demonstrated here can be applied to account for edema explicitly and there by improve the accuracy of clinical dose estimates.
authors.affiliation: Department of Medical Physics, Cross Cancer Institute, Alberta Health Services - Cancer Care and Department of Oncology, Faculty of Medicine, University of Alberta, Edmonton, Alberta, Canada.
authors.forename: Ron S
authors.initials: RS
authors.lastname: Sloboda
authors.forename: N
authors.initials: N
authors.lastname: Usmani
authors.forename: T T
authors.initials: TT
authors.lastname: Monajemi
authors.forename: D M-C
authors.initials: DM
authors.lastname: Liu