Source:Brachytherapy
Author(s): Thomas Brun, Jean-Marc Bachaud, Pierre Graff-Cailleaud, Bernard Malavaud, Daniel Portalez, Christian Popotte, Richard Aziza, Amélie Lusque, Thomas Filleron, Soléakhéna Ken
PurposeTo 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 MaterialsUFB provisional dose plans for small target volumes (<7 cc) were calculated on a prostate training phantom to optimize the seeds number and strength. Clinical UFB consisted in a contour-based nonrigid registration (MRI/Ultrasound) to implant a fiducial marker at the location of the tumor focus. Dosimetry was performed with iodine-125 seeds and a prescribed dose of 160 Gy. On CT scans acquired at 1 month, dose coverage of 152 Gy to the ultra-focal gross tumor volume was evaluated. Registrations between magnetic resonance and CT scans were assessed on the first 8 patients with three software solutions: VariSeed, 3D Slicer, and Mirada, and quantitative evaluations of the registrations were performed. Impact of these registrations on the initial dose matrix was performed.ResultsMean 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, D100% (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. D90% for the prostate had a mean difference of 1.17 Gy. For urethra and rectum, dose limits were far below the recommendations.ConclusionsThis UFB study confirmed the possibility to treat with optimal dose coverage target volumes smaller than 7 cc.
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