Hybrid dosimetry: feasibility of mixing angulated and parallel needles in planning prostate brachytherapy

Pubic arch interference (PAI) often caused inadequate prostate coverage during transperineal brachytherapy using all parallel needles. In this paper, a hybrid implantation approach is presented in which additional angulated needles can be used to avoid PAI. This approach can be applied in prostate brachytherapy using a robotic assisted device. To examine the feasibility of this approach, volume data from three prostate seed implant patients were selected, which represent small, medium, and large prostates. As the blocking area was artificially increased simulating pubic arch overlap, the dosimetry outcomes and ratio of number of angulated needles to the total number of needles were analyzed. The hybrid dosimetry broke down when blocking is over 42%. As the percent of blocking increased, the ratio of the number of angulated needles to the total number of needles increased, while the dosimetry outcomes only had a slight trend of worsening. When close to the breakdown point, the dosimetry outcomes worsen drastically. Therefore, for moderate PAI the hybrid dosimetry is feasible.