Tracking Tag Stabilization with a Small-Diameter Implant in an Edentulous Mandible to Assist Dynamically Navigated Surgery: A case report

This report describes the use of a temporary dental implant to secure a radiographic fiducial marker and patient tracking tag to an edentulous mandible for dynamically guided implant placement into a fibula microvascular free flap. A small diameter dental implant was placed into the anterior mandible to secure a radiographic fiducial marker followed by a patient tag. The patient tag allowed for tracking of the patient’s mandible during placement of endosseous dental implants. Four endosseous dental implants were successfully placed into the edentulous fibula free flap mandibular reconstruction. Dynamic navigation using a small diameter implant to secure radiographic fiducial markers and patient tags provides a novel technique to place implants into an edentulous microvascular free flap with minimal incision and reflection of soft tissue.

Residual Image Registration Error by Fiducial Markers in Accelerated Partial Breast Irradiation Using C-Arm Linac: A Phantom Study

Introduction: External beam accelerated partial breast irradiation (APBI) is an alternative treatment for patients with early-stage breast cancer. The efficacy of image-guided radiotherapy (IGRT) using fiducial markers, such as gold markers or surgical clips, has been demonstrated. However, the effects of respiratory motion during a single fraction have not been reported. This study aimed to evaluate the residual image registration error of fiducial marker-based IGRT by respiratory motion and propose a suitable treatment strategy.Materials & Methods: We developed an acrylic phantom embedded with surgical clips to verify the registration error under moving conditions. The frequency of the phase difference in the respiratory cycle due to sequential acquisition was verified in a preliminary study. Fiducial marker-based IGRT was then performed in 10 scenarios. The residual registration error (RRE) was calculated on the basis of the differences in the coordinates of clips between the true position if not moved and the last position.Results: The frequencies of the phase differences in 0.0–0.99, 1.0–1.99, 2.0–2.99, 3.0–3.99, and 4.0–5.0 mm were 23%, 24%, 22%, 20%, and 11%, respectively. When assuming a clinical case, the mean RREs for all directions were within 1.0 mm, even if respiratory motion of 5 mm existed in two axes.Conclusions: For APBI with fiducial marker-based IGRT, the introduction of an image registration strategy that employs stepwise couch correction using at least three orthogonal images should be considered.

Prostate deformation during hypofractionated radiotherapy: an analysis of implanted fiducial marker displacement

Background To report prostate deformation during treatment, based on an analysis of fiducial marker positional differences in a large sample. Material and methods This study included 144 patients treated with prostate stereotactic body radiation therapy after implantation in each of 4 gold fiducial markers (FMs), which were located and numbered consistently. The center of mass of the FMs was recorded for every pair of X-ray images taken during treatment. The distance between each pair of fiducials in the live X-ray images is calculated and compared with the respective distances as determined in the CT volume. The RBE is the difference between these distances. Mean RBE and intrafraction and interfraction RBE were evaluated. The intrafraction and intefraction RBE variability were defined as the standard deviation, respectively, of all RBE during 1 treatment fraction and of the mean daily RBE over the whole treatment course. Results We analyzed 720 treatment fractions comprising 24,453 orthogonal X-ray image acquisitions. We observed a trend to higher RBE related to FM4 (apex) during treatment. The fiducial marker in the prostate apex could not be used in 16% of observations, in which RBE was > 2.5 mm. The mean RBEavg was 0.93 ± 0.39 mm (range 0.32–1.79 mm) over the 5 fractions. The RBEavg was significantly lower for the first and second fraction compared with the others (P < .001). The interfraction variability of RBEavg was 0.26 ± 0.16 mm (range 0.04–0.74 mm). The mean intrafraction variability of all FMs was 0.45 ± 0.25 mm. The highest Pearson correlation coefficient was observed between FM2 and FM3 (middle left and right prostate) (R = 0.78; P < .001). Every combination with FM4 yielded lower coefficients (range 0.66–0.71; P < .001), indicating different deformation of the prostate apex. Conclusions Ideally, prostate deformation is generally small, but it is very sensitive to rectal and bladder filling. We observed RBE up to 11.3 mm. The overall correlation between FMs was affected by shifts of individual fiducials, indicating that the prostate is not a “rigid” organ. Systematic change of RBE average between subsequent fractions indicates a systematic change in prostate shape.

A feasibility study on the development and use of a deep learning model to automate real-time monitoring of tumor position and assessment of interfraction fiducial marker migration in prostate radiotherapy patients

Purpose The aim of this study was to assess the feasibility of the development and training of a deep learning object detection model for automating the assessment of fiducial marker migration and tracking of the prostate in radiotherapy patients. Methods and Materials A fiducial marker detection model was trained on the YOLO v2 detection framework using approximately 20,000 pelvis kV projection images with fiducial markers labelled. The ability of the trained model to detect marker positions was validated by tracking the motion of markers in a respiratory phantom and comparing detection data with the expected displacement from a reference position. Marker migration was then assessed in 14 prostate radiotherapy patients using the detector for comparison with previously conducted studies. This was done by determining variations in intermarker distance between the first and subsequent fractions in each patient. Results On completion of training, a detection model was developed that operated at a 96% detection efficacy and with a root mean square error of 0.3 pixels. By determining the displacement from a reference position in a respiratory phantom, experimentally and with the detector it was found that the detector was able to compute displacements with a mean accuracy of 97.8% when compared to the actual values. Interfraction marker migration was measured in 14 patients and the average and maximum ± standard deviation marker migration were found to be 2.0±0.9 mm and 2.3±0.9 mm, respectively. Conclusion This study demonstrates the benefits of pairing deep learning object detection, and image-guided radiotherapy and how a workflow to automate the assessment of organ motion and seed migration during prostate radiotherapy can be developed. The high detection efficacy and low error make the advantages of using a pre-trained model to automate the assessment of the target volume positional variation and the migration of fiducial markers between fractions.

Evaluation of computed tomography settings in the context of visualization and discrimination of low dose injections of a novel liquid soft tissue fiducial marker in head and neck imaging

Background Intraoperative incorporation of radiopaque fiducial markers at the tumor resection surface can provide useful assistance in identifying the tumor bed in postoperative imaging for RT planning and radiological follow-up. Besides titanium clips, iodine containing injectable liquid fiducial markers represent an option that has emerged more recently for this purpose. In this study, marking oral soft tissue resection surfaces, applying low dose injections of a novel Conformité Européenne (CE)-marked liquid fiducial marker based on sucrose acetoisobutyrate (SAIB) and iodinated SAIB (x-SAIB) was investigated. Methods Visibility and discriminability of low dose injections of SAIB/x-SAIB (10 µl, 20 µl, 30 µl) were systematically studied at different kV settings used in clinical routine in an ex-vivo porcine mandible model. Transferability of the preclinical results into the clinical setting and applicability of DE-CT were investigated in initial patients. Results Markers created by injection volumes as low as 10 µl were visible in CT imaging at all kV settings applied in clinical routine (70–120 kV). An injection volume of 30 µl allowed differentiation from an injection volume of 10 µl. In a total of 118 injections performed in two head and neck cancer patients, markers were clearly visible in 83% and 86% of injections. DE-CT allowed for differentiation between SAIB/x-SAIB markers and other hyperdense structures. Conclusions Injection of low doses of SAIB/x-SAIB was found to be a feasible approach to mark oral soft tissue resection surfaces, with injection volumes as low as 10 µl found to be visible at all kV settings applied in clinical routine. With the application of SAIB/x-SAIB reported for tumors of different organs already, mostly applying relatively large volumes for IGRT, this study adds information on the applicability of low dose injections to facilitate identification of the tumor bed in postoperative CT and on performance of the marker at different kV settings used in clinical routine.

Early toxicities of ultrahypofractionated stereotactic body radiotherapy for intermediate risk localized prostate cancer using cone-beam computed tomography and real-time three-dimensional transperineal ultrasound monitoring

Purpose: Image-guided radiotherapy (IGRT) is central to the safe and effective delivery of ultrahypofractionated (UF) stereotactic body radiotherapy (SBRT) for localized prostate cancer. However, the optimal IGRT modality remains uncertain. We aim to study the safety of performing UF-SBRT using cone-beam computed tomography (CBCT) and real-time transperineal ultrasound (TPUS) monitoring. Materials and Methods: We retrospectively review the medical records of 26 patients who had received UF-SBRT for intermediate risk localized prostate cancer in our institution from October 2018 to December 2020. All patients were treated with SBRT without fiducial marker and received 35–40 Gy to the clinical target volume in 5 fractions over 2–5 weeks. CBCT was used to correct for interfraction displacement while intrafraction displacement of the prostate gland was monitored using Elekta Clarity Autoscan TPUS with 4 mm isotropic warning level. All patients also received neoadjuvant and concurrent androgen deprivation therapy for a total of 6 months. The primary endpoints were incidence of acute toxicities and patient reported urinary toxicities in terms of the International Prostate Symptom Score: before (IPSS1), at the completion of (IPSS2), and at 3–6 months (IPSS3) after SBRT. Results: All men were treated and followed up for at least 3 months after SBRT. Patients experienced transient worsening of their urinary symptoms at the end of SBRT but they usually recovered in 3–6 months afterwards. The median IPSS1, IPSS2, and IPSS3 were 12, 12.5, and 8, respectively. One patient developed grade 3 rectal bleeding which was related to underlying hemorrhoid. No other grade 3–4 acute toxicity was observed. Conclusion: It appears safe to deliver UF-SBRT without fiducial marker for prostate cancer patients using CBCT and non-invasive hybrid imaging modalities for positioning and tracking. Longer follow-up is necessary to monitor the treatment efficacy and long-term toxicities.

Risks and Benefits of Fiducial Marker Placement in Tumor Lesions for Robotic Radiosurgery: Technical Outcomes of 357 Implantations

Fiducial markers (FM) inserted into tumors increase the precision of irradiation during robotic radiosurgery (RRS). This retrospective study evaluated the clinical complications, marker migration, and motion amplitude of FM implantations by analyzing 288 cancer patients (58% men; 63.1 ± 13.0 years) who underwent 357 FM implantations prior to RRS with CyberKnife, between 2011 and 2019. Complications were classified according to the Society of Interventional Radiology (SIR) guidelines. The radial motion amplitude was calculated for tumors that moved with respiration. A total of 725 gold FM was inserted. SIR-rated complications occurred in 17.9% of all procedures. Most complications (32.0%, 62/194 implantations) were observed in Synchrony®-tracked lesions affected by respiratory motion, particularly in pulmonary lesions (46.9% 52/111 implantations). Concurrent biopsy sampling was associated with a higher complication rate (p = 0.001). FM migration occurred in 3.6% after CT-guided and clinical FM implantations. The largest motion amplitudes were observed in hepatic (20.5 ± 11.0 mm) and lower lung lobe (15.4 ± 10.5 mm) lesions. This study increases the awareness of the risks of FM placement, especially in thoracic lesions affected by respiratory motion. Considering the maximum motion amplitude, FM placement remains essential in hepatic and lower lung lobe lesions located >100.0 mm from the spine.