Purpose: Brachytherapy (radioactive seed insertion) has emerged as one of the most effective treatment options
for patients with prostate cancer, with the added benefit of a convenient outpatient procedure. The main
limitation in contemporary brachytherapy is faulty seed placement, predominantly due to the presence of intra-operative
edema (tissue expansion). Though currently not available, the capability to intra-operatively monitor
the seed distribution, can make a significant improvement in cancer control. We present such a system here.
Methods: Intra-operative measurement of edema in prostate brachytherapy requires localization of inserted
radioactive seeds relative to the prostate. Seeds were reconstructed using a typical non-isocentric C-arm, and
exported to a commercial brachytherapy delivery system. Technical obstacles for 3D reconstruction on a non-isocentric
C-arm include pose-dependent C-arm calibration; distortion correction; pose estimation of C-arm
images; seed reconstruction; and C-arm to TRUS registration.
Results: In precision-machined hard phantoms with 40-100 seeds and soft tissue phantoms with 45-87 seeds,
we correctly reconstructed the seed implant shape with an average 3D precision of 0.35 mm and 0.24 mm,
respectively. In a DoD Phase-1 clinical trial on 6 patients with 48-82 planned seeds, we achieved intra-operative
monitoring of seed distribution and dosimetry, correcting for dose inhomogeneities by inserting an average of
4.17 (1-9) additional seeds. Additionally, in each patient, the system automatically detected intra-operative seed
migration induced due to edema (mean 3.84 mm, STD 2.13 mm, Max 16.19 mm).
Conclusions: The proposed system is the first of a kind that makes intra-operative detection of edema (and
subsequent re-optimization) possible on any typical non-isocentric C-arm, at negligible additional cost to the
existing clinical installation. It achieves a significantly more homogeneous seed distribution, and has the potential
to affect a paradigm shift in clinical practice. Large scale studies and commercialization are currently underway.