The Possibilities for Solid Tumor Modeling With 3D Printers Are Just Beginning

Jonathan L. Silberstein, MD

Assistant Professor of Urology

Chief, Section of Urologic Oncology Department of Urology

Tulane University School of Medicine

New Orleans, LA

Three-dimensional (3D) printers are on the cusp of revolutionizing the way every doctor practices medicine. While these machines may potentially allow for the creation of patient- specific replacement organs in the distant future, the current applications are already plentiful and many more are imminent.

Although 3D printers come in a variety of shapes and sizes, they all perform by layering successive thin sheets of materials stacked on top of each other to create a physical structure. Cross-sectional imaging, in which successive pictures are taken at different anatomic levels, is ideally suited for use in 3D printing, since each “slice” or cross section is used to generate one layer of the 3D structure. The finer the “cuts” on the CT or MRI, the higher the fidelity of the model to the endogenous structure being recreated.

Typically, the materials used in 3D printing are plastic resins that become malleable when heated, allowing them to be formed into the desired shape and then become fixed when cooled. 3D printers are routinely used to convert cross-sectional imaging of boney structures that have been injured or damaged into 3D physical models to allow orthopedic or maxillofacial surgeons to aid in realignment and reconstruction.

How Tulane Creates and Uses Models

Our group in the Department of Urology at Tulane University School of Medicine has been adapting and developing 3D printing technology for solid organ soft tissue tumor models to aid in patient understanding, surgery selection, medical student and resident education, surgical simulation, and planning and improving surgical outcomes.

As we have created models from different materials with different physical properties, we have realized specific utilities associated with each. Figure 1 depicts one of our first renal models, which we created using a single material and a single color; this is the methodology used by many orthopedic and maxillofacial surgeons to construct boney structures, but it is relatively useless for soft tissue solid organ malignancies. Other than the abnormal contour, there is no way to discern the size, location, or depth of the renal tumor. Figure 2a-d shows some of our preliminary work in which we used a CT scan demonstrating an enhancing renal mass in order to: (1) create a high-fidelity physical 3D model (Figure 2a); (2) demonstrate the normal renal parenchyma in a clear resin and the tumor and blood vessels in a red hue (Figure 2b); and (3) allow resection of the tumor and preservation of the normal renal parenchyma (Figure 2c, 2d). This type of model allows us to highlight both the tumor and the normal renal parenchyma in different colors but with a translucent hue, thus enabling us to determine and demonstrate the depth of invasion (Figure 3a).

To test the utility of 3D tumor modeling, we constructed physical models of renal units with suspected malignancies for five patients who then underwent partial nephrectomy (4 robotic and 1 open). Average ischemia time was 21 minutes, nephrectomy score was 6.8, and all margins were negative. We found that analyzing these types of models prior to performing surgery enhanced our ability to conduct organ- sparing surgery. This process works particularly well with respect to robotic surgery since the physical manipulation of the model helps restore the surgeon’s lost sense of tactile sensation of the organ of interest (Figure 3b).¹

Patient Education

While performing this initial study, it became evident that an important added benefit to the creation of an individualized physical 3D model was to enable patients to better understand the operation being recommended to them, along with the associated risks and benefits, so that they can provide a more complete, informed consent to treatment. This is particularly important for renal cell carcinoma, because most patients present with an incidental finding and are asymptomatic at diagnosis. Furthermore, although most patients are candidates for organ-sparing surgery, which would preserve much of their normal renal function, the majority have their entire kidney removed, which potentially sets them up for chronic kidney disease and all of the resulting sequelae. We found that showing a patient an individualized 3D physical model of his or her specific mass gave the patient a much better understanding of the intended surgery, and the patient was more comfortable electing organ-preserving surgery.¹

Medical Education

Medical student education is another critical utility of patient-specific 3D models. To demonstrate this advantage, we asked a large series of medical students with training in radiographic imaging to evaluate various renal masses using traditional cross-sectional imaging and then using our high-fidelity 3D models.

The students used the nephrometry score, a well-established quantitative scoring system for renal masses, to assign values to renal masses based on their maximum diameter, exophytic/ endophytic properties, nearness to the collecting system, and location of mass relative to polar lines. Students scored much closer to experts and had dramatically reduced variation between one another when using the 3D models as compared with standard imaging, demonstrating the value of 3D models in the training of those learning how to read and interpret imaging modalities.²

Surgical Simulation

Our most recent work has been to further manipulate the materials used to construct the models so that they more closely approximate the softer spongey texture of renal tissue.^3,4 This is particularly valuable in surgical simulation, as constructing a high-fidelity 3D model unique to a specific patient allows a surgeon a “dry run” before ever touching the patient. While much work still needs to be done, the ability to perform patient-specific surgery simulation prior to partial nephrectomy—a surgery known for its relatively steep learning curve and potential for significant complications—could have a tremendous impact on patient outcome, safety, and resident education.

More Uses on Horizon

3D printing of solid organ tumors is in its infancy and while our work has centered primarily around renal surgery, there is no reason that this technology should be limited to either the kidney or to surgery. In the near future, 3D printing may play an important role in treating all soft-tissue solid tumors, including prostate, lung, and liver cancers. In addition, 3D printing may play an important role for medical oncologists in tumor staging and in characterizing the extent of disease and response to treatment. 3D printing is proving to be an increasingly important tool and we hope to continue to challenge ourselves and others to use it to move our field forward.

References

1. Silberstein JL, Maddox MM, Feibus A, et al. Physical models of renal malignancies using standard cross­sectional imaging and three­dimensional printers: a pilot study [published online June 21, 2014]. Urology. 2014;84(2):268­272.
2. Knoedler M, Feibus A, Lange A, et al. Individualized Physical 3D Kidney Tumor Models Constructed from 3D Printers Result in Improved Trainee Anatomic Understanding. Urology. In press.
3. Maddox MM, Feibus A, Lee BR, et al. Resectable physical 3­D models utilizing 3­D printer technology for robotic partial nephrectomy. To be presented at: American Urological Association Annual Meeting; May 15­19, 2015; New Orleans, LA. Video abstract 15­898.
4. Maddox MM, Feibus A, Lee BR, et al. Malleable physical models of renal malignancies constructed from 3­D print­ ers to allow surgical resection for individualized pre­sur­ gical simulation. To be presented at: American Urological Association Annual Meeting; May 15­19, 2015; New Orleans, LA. Abstract 15­3550.