Internal Fiducial Markers Research Articles

WE-E-J-6C-02: Internal Fiducial Markers Can Assist Dose Escalation in Treatment of Prostate Cancer: Results of Organ Motion Simulations

Purpose: We simulated effects of full (no repositioning) and reduced (using fiducial markers and on‐line repositioning following EPI) uncertainties on dose distributions in PTV, prostate, and organs at risk — bladder and rectum; and evaluated limits for dose escalation if on‐line repositioning is implemented and tight PTV margins are applied. Method and Materials: Three patients' anatomies, with large (68cc), medium (55cc) and small (40cc) prostate volumes were used. PTV margins of 2, 4, 6, 9 and 12mm were tested for a conventional 70Gy/35fr, and dose escalated schedules of 74Gy/37fr and 78Gy/39fr. Setup and organ motion uncertainties were modeled in a stochastic manner to generate a dose population histogram. The outcome of each treatment was then scored based on dose distributions in organs. These have been summarized as equivalent uniform doses (EUD) calculated on survival basis for prostate and effective doses from reduced dose‐volume histograms for bladder and rectum. We deemed dose escalation acceptable as long as the currently observed complication rate was not exceeded. To verify validity of obtained margin prescription, 20 patients were studied with the above simulation methods with acceptable margins only. Results: With reduced positioning uncertainties using fiducials, the dose can be escalated to 78 Gy with a reduced PTV margin of 4mm without compromising tumor control probability. Even if large PTV margins (12mm) were applied and dose was escalated to 78Gy, bladder doses did not exceed tolerance levels. The rectal complication probability is comparable to the currently observed rates or even less if rectal bleeding is proven to show strong volume dependence (parallel model) even treating to 78Gy with 4mm margin. The additional 20 patients studied provided similar results. Conclusion: educed positioning uncertainties using fiducial markers allow us to reduce PTV margin to 4mm and escalate dose to 78Gy with similar or lower rectal toxicity rates.

SU‐FF‐J‐96: The Application of Varian's Markermatch Software in a Retrospective Study of Inter‐Fractional Prostate Motion

Purpose: MarkerMatch is an automated marker match software feature developed by Varian in on‐board imaging. It may calculate inter‐fractional prostate motion with internal fiducial markers identified on CT scans. Before each treatment, a pair of portal images was taken and fiducial markers are identified. Based on the portal image pair, MarkerMatch calculates the optimized couch displacement in 3D to maximally restore the marker positions to their reference positions. To evaluate MarkerMatch's clinical performance, we did a phantom test and a retrospective study on patients implanted with radio‐opaque fiducial markers. Method and Materials: We used a phantom implanted with 4 cylindrical‐shaped markers of 1mm in diameter and 3mm in length. MarkerMatch localizes the markers based on CT images. In order to test MarkerMatch's ability to handle CT images of different quality, we scanned the phantom with four CT spacing. The portal image pair taken before treatment is normally at AP/Lateral gantry angles, but sometimes it is difficult to identify markers from the lateral image. To test MarkerMatch's ability to handle non‐orthogonal portal image pair, we took portal images at 7 different gantry angles. As a preliminary test for the use of Markermatch in clinic, we retrospectively analyzed five patients implanted with 2–3 gold markers based on 43 pairs of weekly setup portal images. Results: In our phantom test, MarkerMatch is able to measure overall marker displacements within 1mm in each direction, regardless of the spacing used in the CT scans. Using different gantry separation angles, the measured overall marker displacements agree with each other within 1mm. Retrospective analysis of five patients is also presented. Conclusion: Initial studies indicate that MarkerMatch is robust in detecting and analyzing patient motion in 3D and can provide valuable information of inter‐fractional prostate motion in clinic. Conflict of Interest: Funded in part by Varian Research Grant.

Comparison of Three Methods of Targeting the Subthalamic Nucleus for Chronic Stimulation in Parkinson's Disease

The success of subthalamic nucleus (STN) surgery for Parkinson's disease depends on accuracy in target determination. The objective of this study was to determine which of the following techniques was most accurate and precise in identifying the location for stimulation in STN deep brain stimulation surgery that is most clinically effective: direct targeting, indirect targeting using the positions of the anterior and posterior commissures, or a technique using the red nucleus (RN) as an internal fiducial marker. We reviewed 14 patients with Parkinson's disease treated with bilateral STN deep brain stimulation (28 STN targets). Electrode implantation was based on direct and indirect targeting using two-dimensional magnetic resonance imaging with refinement using microelectrode recording. Optimal settings, including the contacts used, were determined during the clinical follow-up. The position of the best contact was defined with postoperative magnetic resonance imaging. This location was compared with the modified direct, indirect, and RN-based targets. The mean distances between the targets and the final position of the optimal contact were calculated. The accuracy and variance of each target were analyzed. The mean position of the best contact was x = 12.12 (standard deviation [SD], 1.45 mm), y = -2.41 (SD, 1.63 mm), and z = -2.39 (SD, 1.49 mm) relative to the midcommissural point. The mean distance between the optimal contact position and the planned target was 3.19 mm (SD, 1.19 mm) using the RN-based method, 3.42 mm (SD, 1.34 mm) using indirect targeting, and 4.66 mm (SD, 1.33 mm) using a modified direct target. The mean distance between the optimal contact and the RN-based target was significantly smaller than the mean distance between the optimal contact and the direct target (post hoc with Tamhane's correction, P < 0.001) but not between the optimal contact and the indirect target. The RN-based target had the smallest variance (F test, P < 0.001), indicating greater precision. The use of the RN as an internal fiducial marker for targeting the optimal region of STN stimulation was reliable and closely approximates the position of the electrode contact that provides the optimal clinical results.

Three-dimensional conformal setup (3D-CSU) of patients using the coordinate system provided by three internal fiducial markers and two orthogonal diagnostic X-ray systems in the treatment room

Three-dimensional conformal setup (3D-CSU) of patients using the coordinate system provided by three internal fiducial markers and two orthogonal diagnostic X-ray systems in the treatment room

High dose three-dimensional conformal boost (3DCB) using an orthogonal diagnostic X-ray set-up for patients with gynecological malignancy: a new application of real-time tumor-tracking system

The feasibility and accuracy of high dose three-dimensional conformal boost (3DCB) using three internal fiducial markers and a two-orthogonal X-ray set-up of the real-time tumor-tracking system on patients with gynecological malignacy were investigated in 10 patients. The standard deviation of the distribution of systematic deviations (Σ) was reduced from 3.8, 4.6, and 4.9mm in the manual set-up to 2.3, 2.3 and 2.7mm in the set-up using the internal markers. The average standard deviation of the distribution of random deviations (σ) was reduced from 3.7, 5.0, and 4.5mm in the manual set-up to 3.3, 3.0, and 4.2mm in the marker set-up. The appropriate PTV margin was estimated to be 10.2, 12.8, and 12.9mm in the manual set-up and 6.9, 6.7, and 8.3mm in the gold marker set-up, respectively, using the formula 2Σ+0.7σ. Set-up of the patients with three markers and two fluoroscopy is useful to reduce PTV margin and perform 3DCB.

Three-dimensional conformal setup (3D-CSU) of patients using the coordinate system provided by three internal fiducial markers and two orthogonal diagnostic X-ray systems in the treatment room

To test the accuracy of a system for correcting for the rotational error of the clinical target volume (CTV) without having to reposition the patient using three fiducial markers and two orthogonal fluoroscopic images. We call this system "three-dimensional conformal setup" (3D-CSU). Three 2.0-mm gold markers are inserted into or adjacent to the CTV. On the treatment couch, the actual positions of the three markers are calculated based on two orthogonal fluoroscopies crossing at the isocenter of the linear accelerator. Discrepancy of the actual coordinates of gravity center of three markers from its planned coordinates is calculated. Translational setup error is corrected by adjustment of the treatment couch. The rotation angles (alpha, beta, gamma) of the coordinates of the actual CTV relative to the planned CTV are calculated around the lateral (x), craniocaudal (y), and anteroposterior (z) axes of the planned CTV. The angles of the gantry head, collimator, and treatment couch of the linear accelerator are adjusted according to the rotation of the actual coordinates of the tumor in relation to the planned coordinates. We have measured the accuracy of 3D-CSU using a static cubic phantom. The gravity center of the phantom was corrected within 0.9 +/- 0.3 mm (mean +/- SD), 0.4 +/- 0.2 mm, and 0.6 +/- 0.2 mm for the rotation of the phantom from 0-30 degrees around the x, y, and z axes, respectively, every 5 degrees. Dose distribution was shown to be consistent with the planned dose distribution every 10 degrees of the rotation from 0-30 degrees. The mean rotational error after 3D-CSU was -0.4 +/- 0.4 (mean +/- SD), -0.2 +/- 0.4, and 0.0 +/- 0.5 degrees around the x, y, and z axis, respectively, for the rotation from 0-90 degrees. Phantom studies showed that 3D-CSU is useful for performing rotational correction of the target volume without correcting the position of the patient on the treatment couch. The 3D-CSU will be clinically useful for tumors in structures such as paraspinal diseases and prostate cancers not subject to large internal organ motion.

Feasibility of insertion/implantation of 2.0-mm-diameter gold internal fiducial markers for precise setup and real-time tumor tracking in radiotherapy

Purpose To examine the feasibility and reliability of insertion of internal fiducial markers into various organs for precise setup and real-time tumor tracking in radiotherapy (RT). Methods and materials Equipment and techniques for the insertion of 2.0-mm-diameter gold markers into or near the tumor were developed for spinal/paraspinal lesions, prostate tumors, and liver and lung tumors. Three markers were used to adjust the center of the mass of the target volume to the planned position in spinal/paraspinal lesions and prostate tumors (the three-marker method). The feasibility of the marker insertion and the stability of the position of markers were tested using stopping rules in the clinical protocol (i.e., the procedure was abandoned if 2 of 3 or 3 of 6 patients experienced marker dropping or migration). After the evaluation of the feasibility, the stability of the marker positions was monitored in those patients who entered the dose-escalation study. Results Each of the following was shown to be feasible: bronchoscopic insertion for the peripheral lung; image-guided transcutaneous insertion for the liver; cystoscopic and image-guided percutaneous insertion for the prostate; and surgical implantation for spinal/paraspinal lesions. Transcutaneous insertion of markers for spinal/paraspinal lesions and bronchoscopic insertion for central lung lesions were abandoned. Overall, marker implantation was successful and was used for real-time tumor tracking in RT in 90 (90%) of 100 lesions. No serious complications related to the marker insertion were noted for any of the 100 lesions. Using three markers surgically implanted into the vertebral bone, the mean ± standard deviation in distance among the three markers was within 0.2 ± 0.6 mm (range −1.4 to 0.8) through the treatment period of 30 days. The distance between the three markers gradually decreased during RT in five of six prostate cancers, consistent with a mean rate of volume regression of 9.3% (range 0.015–13%) in 10 days. Conclusion Internal 2.0-mm-diameter gold markers can be safely inserted into various organs for real-time tumor tracking in RT using the prescribed equipment and techniques. The three-marker method has been shown to be a useful technique for precise setup for spinal/paraspinal lesions and prostate tumors.

Calculation of rotational setup error using the real-time tracking radiation therapy (RTRT) system and its application to the treatment of spinal schwannoma

Purpose : The efficacy of a prototypic fluoroscopic real-time tracking radiation therapy (RTRT) system using three gold markers (2 mm in diameter) for estimating translational error, rotational setup error, and the dose to normal structures was tested in 5 patients with spinal schwannoma and a phantom. Methods and Materials : Translational error was calculated by comparing the actual position of the marker closest to the tumor to its planned position, and the rotational setup error was calculated using the three markers around the target. Theoretically, the actual coordinates can be adjusted to the planning coordinates by sequential rotation of γ degrees around the z axis, β degrees around the y axis, and α degrees around the x axis, in this order. We measured the accuracy of the rotational calculation using a phantom. Five patients with spinal schwannoma located at a minimum of 1–5 mm from the spinal cord were treated with RTRT. Three markers were inserted percutaneously into the paravertebral deep muscle in 3 patients and surgically into two consecutive vertebral bones in two other patients. Results : In the phantom study, the discrepancies between the actual and calculated rotational error were −0.1 ± 0.5°. The random error of rotation was 5.9, 4.6, and 3.1° for α, β, and γ, respectively. The systematic error was 7.1, 6.6, and 3.0° for α, β, and γ, respectively. The mean rotational setup error (0.2 ± 2.2, −1.3 ± 2.9, and −1.3 ± 1.7° for α, β, and γ, respectively) in 2 patients for whom surgical marker implantation was used was significantly smaller than that in 3 patients for whom percutaneous insertion was used (6.0 ± 8.2, 2.7 ± 5.9, and −2.1 ± 4.6° for α, β, and γ). Random translational setup error was significantly reduced by the RTRT setup ( p < 0.0001). Systematic setup error was significantly reduced by the RTRT setup only in patients who received surgical implantation of the marker ( p < 0.0001). The maximum dose to the spinal cord was estimated to be 40.6–50.3 Gy after consideration of the rotational setup error, vs. a planned maximum dose of 22.4–51.6 Gy. Conclusion : The RTRT system employing three internal fiducial markers is useful to reduce translational setup error and to estimate the dose to the normal structures in consideration of the rotational setup error. Surgical implantation of the marker to the vertebral bone was shown to be sufficiently rigid for the calculation of the rotational setup error. Fractionated radiotherapy for spinal schwannoma using the RTRT system may well be an alternative or supplement to surgical treatment.

Registration accuracy and possible migration of internal fiducial gold marker implanted in prostate and liver treated with real-time tumor-tracking radiation therapy (RTRT)

Background and purpose: We have developed a linear accelerator synchronized with a fluoroscopic real-time tumor-tracking system to reduce errors due to setup and organ motion. In the real-time tumor-tracking radiation therapy (RTRT) system, the accuracy of tumor tracking depends on the registration of the marker's coordinates. The registration accuracy and possible migration of the internal fiducial gold marker implanted into prostate and liver was investigated. Materials and methods: Internal fiducial gold markers were implanted in 14 patients with prostate cancer and four patients with liver tumors. Computed tomography (CT) was carried out as a part of treatment planning in the 18 patients. A total of 72 follow-up CT scans were taken. We calculated the relative relationship between the coordinates of the center of mass (CM) of the organs and those of the marker. The discrepancy in the CM coordinates during a follow-up CT compared to those recorded during the planning CT was used to study possible marker migration. Results: The standard deviation (SD) of interobserver variations in the CM coordinates was within 2.0 and 0.4 mm for the organ and the marker, respectively, in seven observers. Assuming that organs do not shrink, grow, or rotate, the maximum SD of migration error in each direction was estimated to be less than 2.5 and 2.0 mm for liver and prostate, respectively. There was no correlation between the marker position and the time after implantation. Conclusion: The degree of possible migration of the internal fiducial marker was within the limits of accuracy of the CT measurement. Most of the marker movement can be attributed to the measurement uncertainty, which also influences registration in actual treatment planning. Thus, even with the gold marker and RTRT system, a planning target volume margin should be used to account for registration uncertainty.

Cochlear implants: three-dimensional localization by means of coregistration of CT and conventional radiographs.

With use of radiopaque implanted objects as internal fiducial markers, the authors developed and evaluated a technique for coregistering computed tomographic (CT) and computed radiographic images to help determine three-dimensional location information for implant electrodes in the cochlea in phantoms and patients. Three-dimensional positional data from CT were assigned on a radiograph, which permitted identification of individual cochlear electrode locations that were not depicted at CT.

Three-dimensional conformal set-up of prostate cancer by adjustment of actual clinical target volume (CTV) to virtual CTV using three fiducial markers and fluoroscopic real-time tracking system

Purpose: A prototype real-time tracking radiation treatment (RTRT) system with insertion of one internal fiducial marker was shown to be useful in reducing translational error in treating prostate cancer. However, it was not possible to calculate and reduce rotational error using the prototype system. We have developed a new algorithm using three internal markers to measure rotational error and reduce it in the treatment for prostate cancer.

Use of Internal Fiducial Markers in Frameless Stereotactic Navigational Systems during Spinal Surgery: Technical Note

The use of frameless stereotaxy has expanded the spine surgeon's ability to perform surgical procedures with instrumentation in areas of narrow anatomic tolerance. In many circumstances, however, it is difficult to register the frameless stereotactic probe using known anatomic landmarks. This occurs typically because landmarks are indistinct, and congenital or surgical defects limit the availability of anatomic fiducials. We propose an accurate and efficient method for registering the frameless stereotactic probe for spinal surgery when a staged procedure is planned. During the first stage of a planned two-stage procedure, a minimum of four cranial fiducial screws are implanted in the posterior element of each vertebra in which stereotactic registration is desired. Stage 1 is completed, and all suture closure is performed. A computed tomographic scan formatted for the frameless stereotactic unit is obtained postoperatively. In the second stage of surgery, registration is performed using cranial screws as internal fiducial markers. Registration is performed easily and quickly using cranial screws as internal fiducial markers. No more than four registration points are necessary to calibrate the system to accuracy within 1.5 mm. Implantation of fiducial markers during Stage 1 of a complex staged spinal surgery renders the frameless stereotactic navigational system registration extremely fast and accurate. We advocate the technique to enhance the use of frameless navigational systems for reliable and quick registration of the spine.

Use of Internal Fiducial Markers in Frameless Stereotactic Navigational Systems during Spinal Surgery: Technical Note

Use of Internal Fiducial Markers in Frameless Stereotactic Navigational Systems during Spinal Surgery: Technical Note

MRI-guided needle localization: Technique

Magnetic resonance imaging (MRI) is being used increasingly in breast cancer diagnosis. Such indications include the search for a breast primary in women with metastatic carcinoma in the axillary lymph nodes, improving surgical planning in women with a biopsy-proven breast cancer, and in screening very high-risk women. If a suspicious lesion is found by MRI, localization with either directed additional mammographic or sonographic views or with MRI-guided needle localization or biopsy is necessary. We describe the use of a biopsy device with embedded internal fiducial markers. The coordinates for needle placement are calculated by distances between the fiducial markers and the lesion. The technique is simple to master and is aided by the use of a practice phantom.

Migration of the internal fiducial gold marker implanted into prostate and liver treated with real-time tumor-tracking radiation treatment (RTRT)

Migration of the internal fiducial gold marker implanted into prostate and liver treated with real-time tumor-tracking radiation treatment (RTRT)