Emerging Treatment Options for Patients With Metastatic Pelvic Disease: How Advanced Image-Guidance Techniques Impact Procedural Efficiencies and Outcomes

The aim of this article is to highlight a complex musculoskeletal intervention including microwave ablation, percutaneous screw fixation, and cementoplasty. This interview and case report with Brandon Key, MD, Vascular and Interventional Radiologist and Assistant Professor of Radiology at the Medical College of Wisconsin in Milwaukee, Wisconsin, will demonstrate how advanced imaging software applications, including Angio-CT, syngo 2D/3D fusion, segmentation, and syngo Needle Guidance (Siemens Healthineers), improve clinical outcomes while decreasing the amount of contrast and dose to the patient and operator.

IO Learning: 2021;9:E13-E20.

Key words: fusion imaging, image guidance, musculoskeletal intervention, navigation, screw and glue

Tell us about the clinical presentation of patients with metastatic pelvic disease and your clinical approach.

The typical patient presents with either hip or pelvic pain, although some present with incidental lesion seen on imaging. Patients who are deemed to be at significant risk based on imaging may benefit from prophylactic fixation. At the Medical College of Wisconsin (MCW), treatment plans are discussed at a multidisciplinary tumor board comprised of Orthopedics, Radiation Oncology, Interventional Radiology (IR), and Medical Oncology. Pre-operatively, patients are then seen in both IR and Orthopedic clinics to discuss their treatment options.

Depending on the extent of the lesion, patients may undergo ablation with osteoplasty or osteoplasty with screw fixation, termed a “screw and glue.”

For fixation of the acetabulum, there are three main screw corridors that are utilized for fixation: the ischial screw, which fixates the posterior column; the superior ramus screw, which fixates the anterior column; and the supra-acetabular screw, which spans both columns. In terms of ablation modality, the choice is nuanced and depends on adjacent structures. Additionally, it is important to keep in mind that the overlying  goal of ablation is to target areas in the fixation corridors to prevent uninhibited disease progression between other cancer therapies (ie, chemotherapy and radiation) to help consolidate the treatment.

Treatment of sacral lesions involves fixation via the S1 and S2 corridors; most patients who have extensive disease will receive screws in both corridors. Screw fixation and cement delivery in these corridors is challenging as these corridors can be  really tight with the L5, S1, and S2 nerve roots, which are all in close proximity to the treatment zones.

Use of intermittent cone-beam Computed Tomography (CBCT) with syngo Needle Guidance and 3D overlay has facilitated the development of safe, minimally invasive techniques for the fixation of debilitating acetabular and sacral lesions.

This sounds like a very innovative and comprehensive approach to this disease. Is this how these patients have been treated historically?

Historically, patients who had acetabular fractures that progressed to a protrusio were typically treated surgically with a Harrington reconstruction, which involved tumor curettage, cement, and placement of an anti-protrusio cage. It is important to note that the Harrington procedure has high complication rates and involves a long, difficult recovery, especially in patients with metastatic disease. In addition, systemic chemotherapy and radiation must often be delayed to allow for wound healing. At MCW, these patients have a minimally invasive treatment option as a result of collaboration between Orthopedic Surgery and IR. This partnership has allowed this procedure to evolve from a therapy that carried high morbidity to an outpatient procedure where patients are discharged the following morning with minimal restriction.

What makes these procedures so challenging?

These procedures are technically challenging due to the complexity of pelvic anatomy and the tight corridors for which screws are placed. Accurate screw fixation relies upon CT or CBCT with Needle Guidance (Siemens Healthineers, Forchheim, Germany). In addition, the operator must be highly aware of adjacent critical structures in order to avoid collateral damage during ablation, osteoplasty, and screw fixation.

How does imaging impact your ability to treat this complex disease?

Understanding of and proficiency with the advanced software applications on the Siemens platform are essential for these complex MSK interventions. Treatment of this disease using standard fluoroscopy without the assistance of the imaging applications would be quite challenging. The use of intraprocedural CBCT (or CT if working in a combined Angio-CT suite) allows the operator to safely proceed with unorthodox trajectories in very tight corridors for needle placements, which results in procedural success and reduction in complications.

At MCW, we have a Siemens Angio-CT system, which is comprised of a ceiling-mounted angiography unit (Artis Q) as well as a CT scanner (SOMATOM Edge) (Siemens Healthineers). The CT scanner is on floor rails and can be moved over the patient for intraprocedural imaging as needed. There are advantages and disadvantages to each modality. When CT is primarily used for procedures, the operator is limited by the bore size, which cannot accommodate some larger devices and guide pins, while the use of fluoroscopy with intermittent DynaCT offers a little more freedom in that respect. However, CT offers real-time tracking of the K wires, whereas fluoroscopy introduces the possibility of misregistration. There is an interplay between the utilization of DynaCT with 3D image overlay and intermittent CT. User experience and device availability dictate which option is selected.

Can you tell us more about your workspace and your AngioCT system at MCW?

At MCW, we have a Siemens ceiling-mounted angiography system with a sliding-gantry CT. The CT is in an adjacent room that is separated by a sliding garage door. CT can be utilized when needed, but as we have advanced with our screw-fixation techniques in the pelvis and sacrum, we have migrated more toward fluoroscopy for efficiency and ease of use with our devices and tools. CT is advantageous when cross-sectional imaging must be relied upon to safely complete to the procedure. An example of this would be during cement delivery in cases with extensive disease in which cortical landmarks are lost. Use of CT in these cases limits the risk of potential complications.

Our IR suites are also unique because they are located “behind the red line” and maintain OR-level sterility, which allows us to place implants without a compromise in terms of sterility.

Can you elaborate on how you utilize the advanced fusion imaging applications offered on Siemens Healthineers technology?

The advanced applications offered through the Siemens platform have allowed our team to perform this procedure. We begin by importing the preprocedure CT into the Siemens imaging workstation and planning our trajectories. We then acquire a CBCT and perform 3D/3D fusion, which registers the preprocedure CT to the CBCT. This allows us to visualize tumor enhancement as we can see structures on a contrasted CT that we cannot see on a CBCT. Prior to the day of the procedure, we use the preprocedure CT to plan our approach. Therefore, when the preprocedure CT is fused to the CBCT, the planned trajectories and 3D markers are also fused, so we are ready to go, without wasting any time on the day of the procedure planning at the workstation. This method also allows us to segment the tumor(s), which will then be displayed as an overlay on live fluoroscopy. This is particularly useful when treating the pelvis, as fluoroscopic images of the pelvis, particularly the acetabulum, can be difficult to interpret due to multiple overlapping structures. The ability to segment a tumor in three dimensions and overlay it allows one to more accurately know where one is ablating and when one is near danger zones. As the C-arm rotates, the segmented tumor will adjust to the C-arm position and update in real time. It also helps with the osteoplasty; the operator can trace out nerves that are of interest as well as the joint space to ensure safe delivery of cement.

We also use fiducial markers, which are crosshairs that the operator can place on bone entry sites at the imaging workstation that have increased our procedural efficiency. This technique has been invaluable for determining the starting point of the procedure, as a “bulls eye view” is often not obtainable. The fiducial marker provides visual confirmation of bone contact at the desired site. This has proven to be extremely helpful because it can be very challenging to introduce needles and guide pins at the exact desired starting location with fluoroscopy. These 3D markers are displayed on live fluoroscopy and move in alignment with C-arm rotation and angulation.

What impact does the Needle Guidance software have on your cases?

Needle Guidance has been essential to the successful development of this procedure. We typically use three traditional corridors for our screw placements in the pelvis — an ischial screw, a superior ramus screw, and a posterior to anterior screw across the top of the acetabulum. Needle Guidance is essential when placing screws to maintain appropriate position within the desired corridor. The superior pubic ramus screw is one of the most challenging to place, especially in a female pelvis, which is more rounded and often has a very tight corridor. The operator may only have a space of 4-5 mm through which to place a guide pin, and when done in the setting of metastatic disease, the side or borders of the cortex are often extremely difficult to visualize. Needle Guidance is therefore crucial in order to perform these procedures successfully.

Has the Needle Guidance software decreased your procedure times?

Needle Guidance has allowed these procedures to be performed more efficiently and accurately under live fluoroscopy. Without it, it would be almost impossible to place these screws in a traditional OR setting with a C-arm. The corridors in the acetabulum are extremely tight, and there is a lot of potential for error.

Does the Needle Guidance software affect patient fluoroscopy dose?

As the operator gains experience with 3D overlay and cone-beam CT with Needle Guidance, the guide pins can be placed faster and more accurately, resulting in a lower patient radiation dose.

It seems as if the treatment of metastatic pelvic disease has come a long way in a short amount of time. Are there other current or future musculoskeletal indications for this technology?

I have been fortunate to practice at MCW, which has an amazing collaborative relationship with the Orthopedic Surgery team. The “screw and glue” technique (where we ablate, screw fixate using needle guidance and augmented fluoroscopy, and then perform osteoplasty) has been utilized in other places in the body, such as glenoid lesions, clavicles, and sternums. We also utilize CBCT and Needle Guidance to perform many adjunctive pain procedures.

Advances in cancer treatments have led to patients with prostate, breast, colorectal, renal, and even pancreatic cancer living years longer. Unfortunately, this is also accompanied with an increase in the risk of morbidity secondary to both cancer- and therapy-related skeletal events, namely, fractures.¹ This rising population of patients with skeletal-related complications has fostered the development of innovative techniques and multidisciplinary collaboration to address these typically painful, debilitating lesions.

Patients with acetabular metastases with resultant instability may experience significant pain relief and improvement in mobility after stabilization.^2-4 Historically, these patients were palliated with pain medications and in advanced cases, a Harrington-type reconstruction consisting of tumor curettage, cementation, and placement of an antiprotrusio cage.⁵ Emerging data have demonstrated the safety and efficacy of minimally invasive image-guided periacetabular ablation and stabilization, or the “screw and glue” method. This technique merges orthopedic surgical principles with the imaging expertise and skill set of interventional radiologists to perform fixation of poor-quality or tumor-involved bone, which improves pelvic load-bearing strength.⁶ As a result, in contrast with prior open surgical interventions, patients post screw and glue are often discharged the next day, are immediately weight bearing as tolerated, and experience minimal if any disruption or delay of chemotherapy and radiation as there are no large surgical wounds to heal.⁴

The patient was a 59-year-old man with metastatic renal cell carcinoma, diagnosed 7 years prior to presentation, status post radical nephrectomy and multiple lines of systemic therapy. Staging computed tomography (CT) of the chest, abdomen, and pelvis prior to presentation demonstrated a new metastatic lesion involving the left acetabulum for which he was referred to the Orthopedic Surgery (Ortho) clinic. The patient was subsequently seen and evaluated in a combined Interventional Radiology (IR) and Ortho clinic. Upon interview, he endorsed 8/10 pain deep in his left buttock and posterolateral hip, which was worse with weight bearing and required him to ambulate with a cane. On physical exam, he had complete range of motion of the left hip with intact and symmetric strength. He ambulated with a slight antalgic gait using a cane. Review of imaging demonstrated a 2 x 1.8 x 2.9 cm, destructive, lytic lesion of the posterior superior acetabulum, directly in the weight-bearing zone of the joint. There was no soft tissue extension into the joint, fracture, or protrusio (Figure 1).

Procedural preparation and details. Based on imaging and patient presentation, ablation, screw fixation, and osteoplasty of his left acetabular lesion was indicated in order to prevent future collapse, improve mobility, and alleviate pain. At the Medical College of Wisconsin (MCW), in general, there is a standard fashion in which we prepare for our pelvic stabilization cases. Preprocedural cross-sectional imaging is uploaded in the imaging workstation in the IR suite. Trajectories for guide-pin placement, ablation, and cementoplasty are all planned on the preprocedure CT scan prior to the patient entering the IR suite. After the patient is appropriately positioned and prepped, a cone beam CT (CBCT) is obtained, and 3D-3D fusion is performed. The syngo 3D/3D fusion software (Siemens Healthineers) merges the preplanned trajectories, tumor segmentation, and fiducial markers with the patient’s CBCT. While it is possible to perform 2D/3D fusion with the current software, we have found that 3D/3D fusion is more accurate and allows for the evaluation of the lesion being treated for any interval progression, which is critical as this may alter the treatment plan. The procedure is then performed with 3D image overlay, the overlay of objects registered to the patient on the fluoroscopic image, and intermittent CBCTs, which are subsequently fused each time to the previous CBCT.

For this patient, syngo Needle Guidance (Siemens Healthineers) trajectories were drawn extending from the inferior ischium into the iliac for fixation of the posterior column and posterior to anterior extending from the posterior superior iliac spine to anterior inferior iliac spine to buttress the superior joint (Figure 2). Fiducial markers were placed at the bone entry sites; this provides a visual marker to correspond with tactile feedback of contacting the bone at the appropriate site, as often times the bulls-eye view is unable to be obtained due to the steep angles of the intended trajectories. Needle Guidance and proper preprocedural trajectory planning are important, as the chosen corridors may intersect. Live 3D image overlay with Needle Guidance was then used to place a guide pin along the preplanned trajectory through the inferior ischium and into the iliac (Figure 3). The segmented tumor overlaid on the live fluoroscopy image served as a guide not only for guide-pin placement, but also to assess for appropriate placement of the ablation probe, which was directed through a partially inserted screw (Figure 4). Post ablation, a kyphoplasty balloon was inserted and inflated within the ablation cavity, utilizing the segmented tumor overlay to confirm placement of the balloon in the region of interest (Figure 4). The guide pin was then advanced through its complete trajectory and removed. Cement was injected through a cement cannula placed coaxially through the partially inserted screw and cementoplasty was performed with live fluoroscopy (Figure 4). The guide pin was then replaced, and the screw was subsequently advanced over the guide pin to its preplanned destination. Attention was then turned to placement of the supra-acetabular screw. To negate any possible misregistration issues, a CBCT was performed to verify the trajectory for the posterior to anterior screw and a bone trocar was placed using Needle Guidance software with 3D image overlay (Figure 5). The guide pin was then advanced through the trocar and along its predetermined trajectory (note the use of the progression view to place the guide pin at the proper depth in Figure 5). The screw was subsequently placed over the guide pin and completion CBCT was performed to confirm appropriate placement and to assess for possible complications (Figure 6 and Figure 7).

Siemens Healthineers’ advanced imaging software has enabled the development of the screw and glue technique. 3D/3D fusion and Needle Guidance are essential to performing these complex cases. Preprocedure planning of needle trajectories, ablation zones, and cementation portals with subsequent 3D/3D fusion to CBCT streamlines the procedure. Challenging/narrow corridors can be pre-emptively identified, and trajectories meticulously adjusted to avoid potential complication or collision of screws. Interprocedurally, Needle Guidance with 3D image overlay and intermittent CBCT allows for efficient placement of guide pins along preplanned trajectories with reduced doses of radiation compared with CT-guided placement for advanced operators. In addition, in the setting of lytic/destructive lesions, which have eroded cortical landmarks, Needle Guidance with tumor segmentation enables operators to safely place cannulas, ablation probes, and guide pins. Tumor segmentation also provides visual reassurance during ablation and cementation.

Fiducial markers with live augmented fluoroscopy also provide great benefit when used to mark bone entry sites and critical nearby structures. The accurate start of any trajectory into bone is paramount for the overall success of the case. Placing a fiducial marker at the bone entry site provides a visual marker to correspond with tactile feedback of contacting the bone at the appropriate site, which serves as a workaround when the bulls-eye view is unable to be obtained due to the steep angles of the intended trajectory. Additional fiducials marking nearby critical structures, ie, nerve roots, neural foramen, and acetabulum, can facilitate safe delivery of cement with fluoroscopy.

Advanced fluoroscopic imaging applications combined with CBCT have dramatically impacted the treatment of patients with acetabular metastases. The combination of 3D/3D fusion, CBCT, Needle Guidance software, tumor segmentation, and 3D image overlay has led to the development of minimally invasive techniques for stabilization, ablation, and cementoplasty of complex acetabular lesions with significantly positive impact on patient quality of life.

From Froedtert & Medical College of Wisconsin, Milwaukee, Wisconsin.

Disclaimer: The statements by Siemens Healthineers’ customers described herein are based on results that were achieved in the customer’s unique setting. Since there is no “typical” hospital and many variables exist (eg, hospital size, case mix, level of IT adoption) there can be no guarantee that other customers will achieve the same results.

Disclosure: The author has completed and returned the ICMJE Form for Disclosure of Potential Conflicts of Interest. Dr Key reports honoraria from Siemens Healthineers for educational symposium at SIR 2021 and manuscript writing.

The author reports that patient consent was provided for the images used herein.

Address for Correspondence: Brandon Key, MD, Interventional Radiology, Center for Advanced Care, Froedtert Hospital, 8900 West Doyne Ave, Milwaukee, WI 53226. Email: bkey@mcw.edu