Journal of Medical Physics
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ORIGINAL ARTICLE
Year : 2012  |  Volume : 37  |  Issue : 2  |  Page : 81-89

Impact of edema and seed movement on the dosimetry of prostate seed implants


1 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
2 Department of Radiation Oncology, Cross Cancer Institute, Alberta Health Services - Cancer Care and Department of Oncology, Faculty of Medicine, University of Alberta, Edmonton, Alberta, Canada

Correspondence Address:
Ron S Sloboda
Cross Cancer Institute, Room 0418, 11560 University Avenue, Edmonton, Alberta, T6G 1Z2
Canada
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0971-6203.94742

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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.


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