A novel curvilinear approach for prostate seed implantation.

ABSTRACT

PURPOSE: A new technique called "curvilinear approach" for prostate seed implantation has been proposed. The purpose of this study is to evaluate the dosimetric benefit of curvilinear distribution of seeds for low-dose-rate (LDR) prostate brachytherapy. METHODS: Twenty LDR prostate brachytherapy cases planned intraoperatively with VariSeed planning system and I-125 seeds were randomly selected as reference rectilinear cases. All the cases were replanned by using curved-needle approach keeping the same individual source strength and the volume receiving 100% of prescribed dose 145 Gy (V(100)). Parameters such as number of needles, seeds, and the dose coverage of the prostate (D(90), V(150), V(200)), urethra (D(30), D(10)) and rectum (D(5), V(100)) were compared for the rectilinear and the curvilinear methods. Statistical significance was assessed using two-tailed student's t-test. RESULTS: Reduction of the required number of needles and seeds in curvilinear method were 30.5% (p < 0.001) and 11.8% (p < 0.49), respectively. Dose to the urethra was reduced significantly; D(30) reduced by 10.1% (p < 0.01) and D(10) reduced by 9.9% (p < 0.02). Reduction in rectum dose D(5) was 18.5% (p < 0.03) and V(100) was also reduced from 0.93 cc in rectilinear to 0.21 cc in curvilinear (p < 0.001). Also the V(150) and V(200) coverage of prostate reduced by 18.8% (p < 0.01) and 33.9% (p < 0.001), respectively. CONCLUSIONS: Significant improvement in the relevant dosimetric parameters was observed in curvilinear needle approach. Prostate dose homogeneity (V(150), V(200)) improved while urethral dose was reduced, which might potentially result in better treatment outcome. Reduction in rectal dose could potentially reduce rectal toxicity and complications. Reduction in number of needles would minimize edema and thereby could improve postimplant urinary incontinence. This study indicates that the curvilinear implantation approach is dosimetrically superior to conventional rectilinear implantation technique.