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Revisit Seed Nomogram for Real-Time Intraoperative Prostate Brachytherapy

C Yang

C Yang*, Y Chen , S Sim , Monmouth Medical Center, Long Branch, NJ


SU-I-GPD-T-25 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: Current practice overestimated a prostate volume based nomogram to estimate the total activity of intraoperative seed implant (IPSI) brachytherapy. A revised nomogram was created and to analyze reduction of seeds of IPSI by using best fit model.

Methods: 27 patients received ultrasound (US) guided IPSI with I-125 sources (AgX100) at our institution between 2014 and 2016. A modified peripheral loading technique were planned using VariSeed 8.0 (Varian) with a minimum of ≥95% of the prostate volume covered by 144 Gy prescription dose with ≤0.01 cc of the urethra and rectal wall receiving ≥180 Gy. In-house curve fitted nomograms by upper 99% confidence interval (CI) specific to IPSI were calculated for those cases. The correlation implant volume versus the returned seeds is studied for further reduction of seeds, which maintained planning quality with minimum seeds.

Results: Mean number of employed sources was 63±7 sources with an average total activity of 26.9±3.97mCi. The mean pre-plan nomogram predicted an average of 68±4 seeds used with a total activity of 28.5±4.7 mCi; calculated average loaded seeds were 68±3, indicated 7.9% more than necessary to achieve ideal coverage. Our current standard 75 seeds order of lower activity for IPSI including 10% margin may be sub-optimum. The average returned seeds were 11±7, still more than projected. With evaluation of our patients’ prostate volume, 70 seeds with volume correlated seed activity should achieve quality coverage. Compared to the non-IPSI based standard nomogram employed 85 seeds, 17.7% reduction predicted a mean total activity 26.7±5.9%. Further reduction with less seeds will be easier for post implant CT planning, while maintain a better implant quality.

Conclusion: New nomogram for IPSI was validated with 99% CI fitting; ordering less seeds while meeting our planning goals. This nomogram provides a safety margin for enough seeds in OR while delivering excellent plans.

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