New approach of ultra-focal brachytherapy for low- and intermediate-risk prostate cancer with custom-linked I-125 seeds: A feasibility study of optimal dose coverage

Abstract Purpose To present the feasibility study of optimal dose coverage in ultra-focal brachytherapy (UFB) with multiparametric MRI for low- and intermediate-risk prostate cancer. Methods and Materials UFB provisional dose plans for small target volumes ( Results Mean differences between simulated dose plans and extrapolated Bard nomogram for UFB volumes were 36.3% (26–56) for the total activity, 18.3% (10–30) for seed strength, and 22.5% (16–38) for number of seeds. Registration method implemented in Mirada performed significantly better than VariSeed and 3D Slicer ( p  = 0.0117 and p  = 0.0357, respectively). For dose plan evaluation between Mirada and VariSeed, D 100 % (Gy) for ultra-focal gross tumor volume had a mean difference of 28.06 Gy, mean values being still above the objective of 152 Gy. D 90 % for the prostate had a mean difference of 1.17 Gy. For urethra and rectum, dose limits were far below the recommendations. Conclusions This UFB study confirmed the possibility to treat with optimal dose coverage target volumes smaller than 7 cc.