Gynecologic malignancies, including cervical, endometrial, ovarian, vaginal and vulvar cancers, cause significant mortality in women worldwide. The standard care for many primary and recurrent gynecologic cancers consists of chemoradiation followed by brachytherapy. In high dose rate (HDR) brachytherapy, intracavitary applicators and /or interstitial needles are placed directly inside the cancerous tissue so as to provide catheters to deliver high doses of radiation. Although technology for the navigation of catheters and needles is well developed for procedures such as prostate biopsy, brain biopsy, and cardiac ablation, it is notably lacking for gynecologic HDR brachytherapy. Using a benchtop study that closely mimics the clinical interstitial gynecologic brachytherapy procedure, we developed a method for evaluating the accuracy of image-guided catheter placement. Future bedside translation of this technology offers the potential benefit of maximizing tumor coverage during catheter placement while avoiding damage to the adjacent organs, for example bladder, rectum and bowel. In the study, two independent experiments were performed on a phantom model to evaluate the targeting accuracy of an electromagnetic (EM) tracking system. The procedure was carried out using a laptop computer (2.1GHz Intel Core i7 computer, 8GB RAM, Windows 7 64-bit), an EM Aurora tracking system with a 1.3mm diameter 6
DOF sensor, and 6F (2 mm) brachytherapy catheters inserted through a Syed-Neblett applicator. The 3D Slicer and PLUS open source software were used to develop the system. The mean of the targeting error was less than
2.9mm, which is comparable to the targeting errors in commercial clinical navigation systems.
Planned in-situ radiosensitization may improve the therapeutic ratio of image guided <sup>125</sup>I prostate brachytherapy.
Spacers used in permanent implants may be manufactured from a radiosensitizer-releasing polymer to deliver protracted
localized sensitization of the prostate. Such devices will have a limited drug-loading capacity, and the drug release
schedule that optimizes outcome, under such a constraint, is not known. This work determines the optimal elution
schedules for <sup>125</sup>I prostate brachytherapy. The interaction between brachytherapy dose distributions and drug
distribution around drug eluting spacers is modeled using a linear-quadratic (LQ) model of cell kill. Clinical
brachytherapy plans were used to calculate the biologic effective dose (BED) for planned radiation dose distributions
while adding the spatial distributions of radiosensitizer while varying the temporal release schedule subject to a
constraint on the drug capacity of the eluting spacers. Results: The greatest increase in BED is achieved by schedules
with the greatest sensitization early in the implant. Making brachytherapy spacers from radiosensitizer eluting polymer
transforms inert parts of the implant process into a means of enhancing the effect of the brachytherapy radiation. Such
an approach may increase the therapeutic ratio of prostate brachytherapy or offer a means of locally boosting the
radiation effect without increasing the radiation dose to surrounding tissues.