  Purpose: Many planning methods for high dose rate (HDR) brachytherapy
treatment planning require an iterative approach. A set of computational
parameters are hypothesized that will give a dose plan that meets dosimetric
criteria. A dose plan is computed using these parameters, and if any dosimetric
criteria are not met, the process is iterated until a suitable dose plan is
found. In this way, the dose distribution is controlled by abstract parameters.
The purpose of this study is to improve HDR brachytherapy planning by
developing a new approach that directly optimizes the dose distribution based
on dosimetric criteria.
  Method: We develop Inverse Planning by Integer Program (IPIP), an
optimization model for computing HDR brachytherapy dose plans and a fast
heuristic for it. We used our heuristic to compute dose plans for 20 anonymized
prostate cancer patient image data sets from our clinic database. Dosimetry was
evaluated and compared to dosimetric criteria.
  Results: Dose plans computed from IPIP satisfied all given dosimetric
criteria for the target and healthy tissue after a single iteration. The
average target coverage was 95%. The average computation time for IPIP was 30.1
seconds on a Intel(R) CoreTM2 Duo CPU 1.67 GHz processor with 3 Gib RAM.
  Conclusion: IPIP is an HDR brachytherapy planning system that directly
incorporates dosimetric criteria. We have demonstrated that IPIP has clinically
acceptable performance for the prostate cases and dosimetric criteria used in
this study, both in terms of dosimetry and runtime. Further study is required
to determine if IPIP performs well for a more general group of patients and
dosimetric criteria, including other cancer sites such as GYN.
