Room: Exhibit Hall
Purpose: Prostate LDR implants result in initial edema which resolves over time. The edema displaces seeds and prostate tissue, affecting the dose delivery. Most institutions perform a post-implant CT scan and compute dosimetry assuming static seed and prostate tissue locations. The aim of this study is to develop multiple edema models based on published data and investigate the effects of edema on the Dâ‚‰â‚€ dose metric for Cs-131 implants.
Methods: LDR prostate edema resolution is well published. Exponential edema models from published data were developed. Clinical seed location data was taken from day 30 post-implant CT scans. From the edema models, the seed locations were displaced to the expected dayâ€™s positions. A â€œrealisticâ€? dose distribution was constructed by summing the individual dayâ€™s dose distributions over a 60 day period accounting for seed and tissue displacement. Sixty â€œstaticâ€? dose distributions were calculated with their respective edematous seed locations assuming the total dose was delivered without seed movement; approximating the post-plan imaging being performed on that day. The Dâ‚‰â‚€ dose metrics were compared and the ideal post-implant scan date evaluated.
Results: For the Prestidge et al. (1998) edema model the results show the â€œrealisticâ€? Dâ‚‰â‚€ to be 98.8% of Rx. The Dâ‚‰â‚€ for day 10, 20, and 30 were 100.0%, 102.5%, and 103.2% respectively. The Tejwani et al. (2012) edema model resulted in the â€œrealisticâ€? Dâ‚‰â‚€ being 93.4% with the day 10, 20, and 30 Dâ‚‰â‚€ being 92.4%, 98.6%, and 103.2%. The ideal post-implant imaging date was day 8 and 11 for the Prestidge and Tejwani models.
Conclusion: The results suggest the ideal date for the post imaging scan to be between day 8 and day 11. The two edema models differed in their reported edema resolution over time, affecting the results. Future work will investigate edema effects on organs at risk.