Intra-operative 3D guidance and edema detection in prostate brachytherapy using a non-isocentric C-arm

Abstract

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 treatment planning 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 six 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 over four additional seeds in the six enrolled patients (minimum 1; maximum 9). 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.

An image‐guidance system for dynamic dose calculation in prostate brachytherapy using ultrasound and fluoroscopy

“…21 For reconstruction, the 0.4 mm mean error of APC-REDMAPS outperforms the 0.6 mm error reported for MARSHAL (Ref. 23) that is utilized in the system presented by Jain et al 18 Finally, for registration, our mean error of 1.3 mm is much better than the 2.9 mm reported for another recent fluoroscopy-to-TRUS registration algorithm. 31 As mentioned previously, there are ten cases when our seed segmentation algorithm performs poorly due to radio-opaque implants or objects in the field of view.…”

“…Recently, Jain et al 18 has proposed a prototype imageguidance system based on TRUS and mobile nonisocentric C-arm fluoroscopy. A central component to their system is the fluoroscope tracking fiducial (FTRAC), 19 a tube compactly composed of several radio-opaque features that innovatively serves the dual purpose of recovering poses from the nonencoded C-arm needed for seed reconstruction and providing the necessary link between the fluoroscopy and ultrasound coordinate systems that is needed for mechanical registration.…”

“…While a rough registration may be achieved, it is reported that an FTRAC-based system has an undesirable mean absolute system error of 4 mm in a training phantom, due to mechanical precalibration errors or biases that may be present during seed reconstruction. 18 The error is likely to be greater in patients as a result of prostate deformation, since the TRUS probe must be inserted to capture TRUS images but removed to capture fluoroscopic images. Other components of the FTRAC system are also problematic.…”

A dynamic dosimetry system for prostate brachytherapy

“…These problems can be avoided with a dynamic dosimetry system that during the operation would accurately locate seeds already implanted and guide the surgeon to place seeds yet to be implanted [2]. Several research groups have sought to produce such a system, but arguably the most promising one yet was published by Jain et al [3] involving the combined use of a clinical ultrasound scanner and a non-isocentric mobile C-arm, two imaging devices that are ubiquitous in operating rooms across clinics.…”

Point-to-Volume Registration of Prostate Implants to Ultrasound

“…Lead markers attached to the probe [5] or radio-opaque fiducials attached to the guiding template [6] have been proposed in the past for ultrasound-fluoroscopy registration. However, markers or fiducials need segmentation and their images may overlap with the seeds and complicate the seed reconstruction.…”