Background and purpose: The purpose of this study is to investigate the feasibility of adequate dose coverage in permanent prostate brachytherapy using divergent needle insertion methods. These methods can be useful in magnetic resonance imaging (MRI) guided needle insertion techniques to avoid pubic arch interference.
Methods and materials: MRI data were collected from 10 patients with T1-T2 prostate cancer. An inverse planning algorithm based on simulated annealing was used to optimize the dose distribution for three needle insertion methods: divergent needles with a single rotation point, divergent needles with a double rotation point, and current parallel needle insertion method. The dose constraints were based on our clinical criteria and the recent ESTRO/EAU/EORTC recommendations.
Results: If the planning target volume (PTV) surrounded the prostate and only intraprostatic seeds were allowed, the mean PTV volume that received 100% of the prescribed dose (V(100)) was 99% for all needle insertion methods. If the PTV was increased to the prostate with a 3mm margin, the mean PTV V(100) equalled 94%, 95%, and 94% for the single rotation point, double rotation point and current parallel needle insertion method, respectively. If in the latter case the tips of the seeds were placed 3mm outside the apex and base of the prostate, the mean PTV V(100) was 96% for all needle insertion methods.
Conclusion: This planning study shows that it is feasible to generate an adequate dose coverage using divergent needle insertion methods.