Electromagnetic Transponders in Prostate Cancer Treatment - Literature review Example

Electromagnetic transponders are increasingly being utilized in pro cancer treatment by implanting electromagnetic transponders into a patient’s prostate gland during radiation therapy in order to provide real time tracking and localization. This is particularly important in enhancing accurate delivery of post- prostatectomy radiation. Compared to the other alternatives, the technique is particularly preferred it allows for enhanced localization of the specific targeted area thereby allowing for the delivery of maximum radiation dose while at the same time minimizing the exposure of the patients surrounding non-targeted normal tissues to radiation. The present research particularly involved reviewing a number of recent publications including journals, books, articles, magazines and databases related to the use of electromagnetic transponders in cancer treatment. KEY TERMS: Implantation, procedure, treatment, therapy, statistics and prostate cancer Literature Review: Electromagnetic Transponders in Prostate Cancer Treatment Introduction Electromagnetic Transponder is an emerging high tech system that is increasingly being used to track the movement of prostate glands particularly during external beam radiation therapy. The technique particularly involves implanting three tiny electromagnetic transponders into a patient’s prostate gland in order to enhance the delivery of post- prostatectomy radiation therapy by providing real time tracking required to ensure accurate treatment of prostate cancer through radiation therapy (Kindblom et al., 2009). According to many experts, the technique is particularly preferred for the post-surgical radiation therapy for prostate cancer because it significantly allows for enhanced localization of the specific targeted area thereby allowing for the delivery of maximum radiation dose while at the same time minimizing the exposure of the patients surrounding non-targeted normal tissues to radiation (Foster, Pistenmaa and Solberg, 2012, p.2924). The present literature paper particularly focused on a comprehensive review of relevant recent publications such as journals, books, articles, magazines, databases and other professional manuscripts related to the theory, practice and use of electromagnetic transponders in cancer treatment. Finally, the findings of the literature review were then analyzed and clustered based on the key major themes namely the oncologic and functional outcomes of electromagnetic transponders, placement of electromagnetic transponders in prostate cancer treatment as well as the challenges related to the use of electromagnetic transponders in the prostate cancer treatment. Oncologic and Functional Outcomes of Electromagnetic Transponders For the last 15 years, development of electromagnetic tracking systems has grown tremendously from an early need in surgical operations to a more advanced precision radiotherapy (Langen et al., 2008). Early image-guided surgery and radiation therapy systems relied on optical tracking. It is a monitoring system with conspicuous limitations; these have led to increased interest in electromagnetic tracking systems for medical purpose. Electromagnetic systems can find use in computer-aided medical procedures by defining position and orientation for guide wires in interventional radiology or catheter placement for bronchoscopy procedures. On the other hand, Foster, Pistenmaa and Solberg (2012) conducted an empirical research that sought to compare the various methodologies and techniques of prostrate localization that are currently being used in prostate cancer treatment in order to determine their differences. A total number of 21 patients undergoing different treatment sessions based on localization techniques including Calypso’s electromagnetic transponder radiation therapy, cone beam CT and orthogonal kV imaging were studied for a given period time and the results recorded. The results revealed that there were little differences between CBCT and Calypso localizations. The authors concluded that prostrate localization based on the use of electromagnetic transponders agrees with radiographic techniques and is therefore suitable for use in high precision prostate cancer radiotherapy (Foster, Pistenmaa and Solberg, 2012, p.2928). Another research on the feasibility of the implementation of electromagnetic transponders in real time tracking during post-surgical radiation therapy was carried out by DAmbrosio et al. (2012). The research particularly presents a report aimed at providing a review of varied non-ionizing technologies intended to constantly localize tumors and patients by reviewing the literary works of earlier researchers. One of the literary materials cited in the report is the study by Mate, Zeller & Douglas (2005) on Feasibility of tracking wireless AC electromagnetic transponders in head and neck cancer environment. Basically, the cited study involved casting of a dental prosthesis from a volunteer followed by use of dental amalgam to fill given teeth. Afterwards, the prosthesis were subjected to the detection array at a position that was adjacent to three transponders and the resulting measurements compared to figures obtained in the absence of dental prosthesis. Despite the amalgam featuring, the system was capable of localizing the transponders even at a distance of 20 cm from the array leading to the conclusion that placing electromagnetic transponders inside a mouthpiece never heightens backscatter dose to an overlying oral mucosa. In an effort to compare how ET compares to other approaches of prostrate localization, Foster, Pistenmaa & Solberg (2012) carried out a study comparing ET to DRR and gold seed implantation. Patients were localized using Calypso and kV/ CBCT orthogonal images within a similar treatment scene thus permitting a direct relation of the used technologies. The distributions of the localization difference were then obtained from the variation in the offsets that were established by Calypso and CBCT/kV imaging. The key findings of the study were that the fraction of localization differences below 3 mm was 0.86, 0.84 and 0.96 in case of the CBCT-Calypso based comparison and 0.95, 0.94 and 0.97 in case of the kV OBI-Calypso based comparison. The findings lead to the conclusion that use of electromagnetic transponders to localize prostate cancer is in harmony with the radiographic techniques in addition to every technology being fit for high-precision radiotherapy. A similar study in ET positioning was conducted by Litzenberg et al. (2007). The study was intended to establish the relative positional stability associated with ET employed in constant electromagnetic localization plus tracking of volumes in radiation therapy. 58/60 transponders implanted depicted no meaningful migration from their target locations. Of the remaining two, one transponder appeared to have been implanted inside the venous plexus with the other implanted inside the urethra. Interestingly, the two cases never resulted into any clinical after effects between the patients. Further, an analysis encompassing the planning CT scan alongside every subsequent distance measurement revealed that the inter-transponder distance bore a standard deviation of < or =1.2 mm for a timeframe of 1 month following the completion of the therapy thus leading to the conclusion that use of a similar implant procedure plus fundamental guidelines whilst placing transponders inside the prostrate helps in guaranteeing minimal migration. On the other hand, Keal et al. (2014) carried out a study that was intended to provide a report on the quality assurance, clinical process, dosimetric and geometric outcomes of the initial ET implementation guided by MLC tracking. The study found that the sum of in-room time tuned to 21 minutes out of which 2 minutes was used for beam delivery. Moreover, there were never any beam holds nor did MLC tracking require extra time. Further, analysis of the dose construction delivered through MLC tracking depicted comparable target does and isodose volume histograms to the designed treatment plus a 0.046 rise inside the fractional rectal V60. On the other hand, the motionless dose reconstruction depicted a 0.3 rise within the fractional rectal V60 from the designed treatment. The study concluded that the medical world has already devoted efforts towards translating electromagnetic transponder-guided MLC tracking for use in clinics thus representing a milestone in enhancing the dosimetric and geometric accuracies associated with ET. Kupelian, Willoughby and Mahadevan (2007) argue that the most prevalent use of electromagnetic tracking technology in radiation therapy is with the localization and tracking systems. The system is offered through the Calypso Medical Technologies (Calypso Medical Technologies, Inc. Seattle, WA). The food and drug administration (FDA) approved the functionality of the system particularly for use in post-prostatectomy prostate radiation therapy. Other important electromagnetic tracking systems for linear accelerator radiotherapy, have been developed by Micro pods Medical (Sweden) and Northern Digital Inc. (Waterloo, Canada). But many of these are investigational devices not cleared for sale in the world for use as tumor tracking devices in radiation oncology (Mingyao et al., 2012, p.1041). The issue of prostate cancer in the world presents one of the heaviest burdens ever witnessed by man since its first diagnosis. It is also the second most lethal coming after lung cancer in terms of deaths reported (Siegel et al., 2011, p.214). In most cases, objective for implantation of electromagnetic transponders is to focus a therapeutic amount of radiation to the targeted tissue while strictly limiting toxicities to the adjacent structures. Localization of the intended target is yet another challenge that practitioners have to contend for a solution (Murphy et al, 2008). For instance, the patients being treated with primary radiotherapy treatment (RT) for prostate cancer exhibit the variations in position day by day; bladder and rectal volumes usually influence this. The outcome means that targeting prostate fosse after RP is the most difficult as it is subject to motion and position errors. It was due to the bony pelvic anatomy, rectal distensions and bladder volumes. In response to these challenges, the placement of radiopaque fiducial marker and electromagnetic transponders introduced an instrumental method (Trock, Han and Freedland, 2007, p.612) say that the technique above helps improve prostate localization and makes the daily target during the prostate cancer RT treatment. In favor of hope to cancer treatment, this method shows complexity in the technical aspect of the feasibility standards that appear to be improving the precision of prostate cancer treatment. Prostate localization has an extensive study, and several different technologies find use for daily localization. The techniques include trans-abdominal ultrasound, X-ray portal imaging, and kilo-voltage and megavoltage cone beam CT. These imaging techniques have allowed the therapist to determine the direction and magnitude of the setup error and correct it before the treatment launches. Studies conducted have been on the forefront in outlining the positives of the several methods; as a whole; localization uncertainties range up to 0.5 cm in each direction (Paul et al, 2014, p.209). While many of the localization techniques have their own limitations, ultrasound has emerged as a popular prostate localization methodology in the radiotherapy it is considered to be noninvasive. Placement of Electromagnetic Transponders in Prostate Cancer Treatment Litzenberg et al. (2007) point out that the placement of electromagnetic transponders is precisely an out-patient procedure performed under the influence of local anesthesia in the standard office setting. The included risks are of pathological features such as extra-capsular extension, positive surgical margins, and seminal vesicle invasion. On the other hand, salvage therapy is defined as RT delivered to patients with detectable and or rising PSA after surgery. Before proceeding to the treatment of trans-rectal, and its implantation, the patients are typically advised to complete a consultation with a urologist (Sawant, Smith and Venkat, 2009). The radiation oncologist has a requirement to give a description of the possible techniques of the transponder implantation together with the process of post-RP radiation therapy. As a pertinent procedure to the patients, the initial process starts with evaluating the patient through a simulation from a magnetic resonance imaging (MRI). The procedure is on a prostate bed with the patient placed in a supine position while immobilized. The CT slices possess a thickness of about 1.5 mm for Calypso Beacons implanted patients. The contouring and combining of the prostate and proximal seminal vesicles constitute the CTV, a uniform PTV expansion. A closed 1.5T MRI simulator finds use in the acquisition of a non-contrast volumetric scan. The approximate measure of the scan is about 1cm above the bladder to 1cm below the penile bulb, using 3mm axial slice thickness with a T2 weighted 3-dimensional turbo spin-echo sequence. Finally, the MRI images are processed for image distortion correction by utilizing the gradient distortion correction software. Immediately after the imaging study, the patient could be ready for either calypso beacon or any other technique (Paul et al., 2014, p.2018). As a final step prior to transponder placement, some patients may be put on assessment tests scores administered by either urologists or sexual health practitioners. All these tests are significant in evaluating toxicities, as well as to monitor, the side effects during and after the completion of the radiation therapy. Challenges of Electromagnetic Transponders in Prostate Treatment Electromagnetic transponder is still a new form of technology in radiation tumor oncology. For this reason, clinical applications and clinical experience are both very minimum. Some of the major challenges of incorporating electromagnetic tracking into radiation therapy are due to scantily available technologies. For instance, currently it is only Calypso System whom is the sole FDA-approved electromagnetic tracking system used in radiation oncology, this means that development resources are quite limited making the advancement probably a pipe dream (Zhu , Bourland and Yuan, 2009). It is a challenge in itself to note that electromagnetic tracking has only a recent approval for use in prostate cancer treatment. Any use at other disease sites must be approved and monitored by the FDA and the local IRB. While there is a utility in tracking the prostate, there is more potential benefit at other disease sites mentioned previously. The development of techniques to treat these clinical sites, along with the regulatory approval to do so, needs some addressing so as to open new avenues for treatment of other diseases using the same technology. Other technical challenges that cannot separate the electromagnetic tracking systems relate to the electromagnetic array (Paul et al, 2014). In what is already being seen, the current electromagnetic tracking system has the arrays that rest directly above the prostate cancer patient. The point of convergence is of the array’s location and RF transponder’s position relative to the range. The electromagnetic tracking system provides to the actual room coordinate system and, further, the transponder’s position relative to iso-center. Another challenge with the electromagnetic tracking systems is in the limited field of view (FOV) with the array. According to Shimizu et al. (2001), the current FOV limitation of the available system is not a critical problem when treating the prostate. The intended goal of the system; if new clinical indications and limitations are to have an implementation will need some checking. More importantly, the flat-field generator should have a place in a location adjacent to the patient. No interference should be from the electrical or ferrous objects in the accelerator room (Van, 2004). In addition, another challenge to electromagnetic tracking systems is regarding the RF device size. With the currently available RF transmitter device, its large size allows for high signal to noise. However, the 8 mm length *2 mm diameter device size requires a 14-gauge needle for trans-perineal implantation. The consideration is relatively large for transcutaneous needle insertion for areas such as the liver or bronchoscopic insertion into the lung (Shimizu et al, 2001). The risk of pneumothorax with transcutaneous approaches is estimated to be in the 20%-30% range and even higher (40%-50%) in patients with obstructive airway disease (Kupelian, Forbes and Willoughby, 2007). The risk of pneumothorax is significantly reduced with transbronchial fiducial placement in the lung, even in peripheral lesions under fluoroscopic guidance. Further, when taking into consideration follow-up imaging studies of patients, the RF transmitter’s relatively large ferrite core. Finally, another challenge to electromagnetic transponder is with competing technologies that may provide tracking via different delivery system (Levitt, 2011). Although radiofrequency-based electromagnetic tracking systems can effectively be used in real time to track tumor location due to their fast update rate, there are a number of emerging technologies are continuously being developed which may provide a similar tracking mechanism. One such remarkable technology being developed by Navotek Inc. (Navotek Inc., Israel) provides the ability to track targets within the body. Navotek is developing a gantry mounted radioactive fiducial tracking system that is reported to provide sub-millimeter accuracy for patient localization and monitoring (Shchory et al., 2008). On the other hand, Noel et al. (2010) argues that dangerous fiducial tracking is increasingly challenging technologies such as electromagnetic tracking due to the technical advancements in implantable radioactive materials and localization involved in these technologies. However, this technology may also have its own limitations such as its inability to provide sufficient rotational information and information on possible organ deformation. Conclusions and Recommendations In conclusion, the use of electromagnetic transponders in prostate cancer treatment remains a promising technology that has the potential of enhancing the localization and allowing for the delivery of maximum radiation dose while at the same time minimizing the exposure of the patients surrounding non-targeted normal tissues to radiation. A significant paradigm shift is now a fundamental need since the exposure of the larger population continues to be a risk as the baby boomers are on a continuous aging cycle. An additional requirement is a combination of strategies to a more effective treatment in the near future. Generally, a universal endorsement may find a way through this achievement. The recommendation of annual general screening intervals on prospect cancer screening and treatment may present a modification based on a patient’s characteristics. Finally, the issue selection in relation to prostate cancer faces controversies. 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