Summary
Here, a new method of establishing a personalized 3D-printed model for preoperative evaluation of thyroid surgery is proposed. It is conducive to preoperative discussion, reducing the difficulty of thyroid surgery.
Abstract
The anatomic structure of the surgical area of thyroid cancer is complex. It is very important to comprehensively and carefully evaluate the tumor location and its relation with the capsule, trachea, esophagus, nerves, and blood vessels before operation. This paper introduces an innovative 3D-printed model establishment method based on computerized tomography (CT) DICOM images. We established a personalized 3D-printed model of the cervical thyroid surgery field for each patient who needed thyroid surgery to help clinicians evaluate the key points and difficulties of the surgery and select the operation methods of key parts as a basis. The results showed that this model is conducive to preoperative discussion and the formulation of operation strategies. In particular, as a result of the clear display of the recurrent laryngeal nerve and parathyroid gland locations in the thyroid operation field, injury to them can be avoided during surgery, the difficulty of thyroid surgery reduced, and the incidence of postoperative hypoparathyroidism and complications related to recurrent laryngeal nerve injury reduced too. Moreover, this 3D-printed model is intuitive and aids communication for the signing of informed consent by patients before surgery.
Introduction
Thyroid nodules are one of the most common endocrine diseases, among which thyroid cancer accounts for 14%-21%1. The preferred treatment for thyroid cancer is surgery. However, because the thyroid gland is located in the anterior cervical area, there are important tissues and organs close to the thyroid gland in the operation area, such as the parathyroid gland, trachea, esophagus, and cervical great vessels and nerves2,3, making the operation relatively difficult and risky. The most common surgical complications are a decrease in parathyroid function caused by parathyroid function injury or mis-resection and hoarseness caused by recurrent laryngeal nerve injury4. The reduction of the above-mentioned surgical complications has always been an objective for surgeons. The most common imaging method before thyroid surgery is ultrasound imaging, although its display of the parathyroid gland and nerve is very limited5. In addition, the variation in the position of the parathyroid gland and the recurrent laryngeal nerve in the thyroid surgery area is very high, which hinders identification6,7. If the anatomical position of each patient can be clearly displayed to the surgeon through the model in real time during the operation, it will reduce the operational risk of thyroid surgery, reduce the incidence of complications, and improve the efficiency of thyroid surgery.
In addition, it is also challenging to thoroughly explain the surgical process to patients before surgery. Some inexperienced surgeons find it difficult to explain and convey the precise details of the operation to patients, especially because of the complexity of the thyroid gland and its surrounding structures. Each patient has their own unique anatomical structure and personal needs8. Therefore, a personalized 3D thyroid model based on the real anatomy of the patient can effectively help patients and clinicians. Currently, the majority of the products on the market are mass-produced based on plane diagrams. By utilizing 3D printing technology to produce a patient-specific model that reflects each patient's individual medical needs, this model can be used to evaluate the actual condition of patients with thyroid cancer and help surgeons better communicate the nature of the disease with patients.
3D printing (or additive manufacturing) is a three-dimensional construction built from a computer aided design model or digital 3D model9. It has been used in many medical applications, such as medical devices, anatomical models, and drug formulation10. Compared to traditional imaging, a 3D printing model is more visible and more legible. Therefore, 3D printing is increasingly being used in modern surgical procedures. Commonly used 3D-printed technologies include vat polymerization-based printing, powder-based printing, inkjet-based printing, and extrusion-based printing11. In vat polymerization-based printing, a specific wavelength of light is irradiated onto a barrel of light-curing resin, which locally cures the resin one layer at a time. It has the advantages of material saving and fast printing. Powder-based printing relies on localized heating to fuse the powder material for a denser structure, but it also leads to a significant increase in printing time and cost, and is currently in limited use12. Inkjet-based printing uses a precise spraying of droplets onto the substrate in a layer-by-layer process. This technology is the most mature and has the advantages of high material compatibility, controllable cost, and fast printing time13. Extrusion-based printing extrudes materials such as solutions and suspensions through nozzles. This technique utilizes cells and, therefore, has the highest soft tissue-mimicking capabilities. Due to the higher cost and bio-affinity, it is mainly used in the field of tissue engineering and less frequently in surgical organ models14.
As a result, we chose the "White Jet Process" printing technology, based on the complexity of the thyroid and its surrounding structures and the surgical schedule. This technology combines the advantages of vat polymerization-based printing and inkjet-based printing, and offers high precision, fast printing, and low cost, making it a good fit for thyroid surgery. The aim of this protocol is to make a 3D-printed thyroid cancer model, improve the prognosis of patients by providing sufficient information about the anatomical structure and variation of patients, and better inform doctors and patients about all the conditions related to the surgical process.
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Protocol
This study did not need approval to perform or any sort of consent from the patients to use and publish their data, because all the data and information in this study and video were anonymized.
1. Collection of image data
- Scan the patient's thyroid by enhanced computerized tomography (CT) to obtain the image data in DICOM format. Ensure that this process is done within 1 week before the operation and control the slice thickness so that it is ≤1 mm.
2. Processing of DICOM data
- Import the scanned patient image data into the software (see Table of Materials) and set the appropriate threshold according to the difference in gray value between the thyroid gland and surrounding tissues or organs. As different gray values are reflections of differences in the density of different areas of the human body, set the grayscale threshold (unit: hu; on the software) to 226-1,500 to present the bone image; set the threshold to -200-226 to show the thyroid gland image. Let the software automatically identify the boxed area, or manually outline the boundary of the target area if the recognition is not satisfactory.
NOTE: Mimics automatically select the thyroid region and use the 3D region growth technology to segment the image and calculate the 3D reconstruction. At the same time, the 3D image is optimized to reduce the roughness and the sense of steps to obtain a natural, smooth, and authentic 3D digital visualization model, which enables a more straightforward observation of the 3D model for surgeons. - Generate STL files from the reconstructed data model. Choose the reconstructed model in the software, click Export in the file dock, and choose STL as the exporting file format. Finally, generate the STL files successfully.
3. Medical-engineering interaction
- Send the reconstructed 3D model preview to the doctors, who will confirm the applied requirements and anatomical structure of the 3D model and give feedback to the modeling engineer if a modification is needed. After receiving confirmations from the doctors, proceed to the production preparation stage.
4. 3D printing (Supplemental File 1)
- Transfer the STL file data to the colorful material 3D printer and complete the parameter presets (such as printing mode, slice stroke thickness, support method, and model coloring) through the supporting 3D printing slicing software.
- Select the printing model according to the type of finished products (color printing models usually use White Jet Process technology, while photosensitive resin usually uses Digital Light Procession).
- Select slice stroke thickness parameter according to the thickness of the products (here, from 24 µm to 36 µm).
- Choose the support method according to the fineness of the printing model: Overall support (better protection and less damage to fine details) or Partial support (which saves materials).
- Select model coloring using the color palette function on the printer. Unify the arteries with red color 255 and the veins with blue color 255.
NOTE: As other parts such as the tumor lesion are not strictly standard, surgeons can select a color according to their needs or preference.
- Fill in hard light curing resin in the 3D printer (see Supplemental Table S1), debug the printing platform, and print using White Jet Process technology. After printing, take out the preliminary printed thyroid model.
NOTE: The White Jet Process technology is based on the principle of inkjet printing, where a thin layer of photosensitive resin is printed out in one jet and then irradiated with a specific wavelength of UV light, causing a rapid polymerization reaction and curing of the photosensitive resin. This process is completed layer by layer until the print is complete.
5. Post-treatment
- Subtract the support structure of the preliminary printed thyroid model. Grind, varnish, and cure the semi-manufactured product to obtain an individualized 1:1 isometric 3D-printed thyroid model.
- Subtracting support structure
- Wearing gloves, break apart the wrapping supports around the preliminary model and remove most of the main body of the supporting structure.
- Put the model into an ultrasonic cleaner with Ca(OH)2 alkaline solution for a 15 min cleaning.
- Put the model into a wet sandblaster and rinse it until the rest of the support structure on the surface is washed away.
- Grinding
- Grind the model with an electric grinder, file, or grinding wheel.
- Varnishing
NOTE: This process consists of spraying and manually painting.- Spray the varnish into large-area color blocks on half of the surface of the model. Manually paint the small-area color blocks with varnish.
- Curing
- Put the model into a UV curing machine for 30 s of curing.
- Take out the model and clean it with 95% alcohol.
NOTE: After the alcohol volatilizes completely, the production is finished.
- Subtracting support structure
6. Delivery
- Package the thyroid model and complete the delivery to the surgeons before surgery.
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Representative Results
This paper presents a protocol for the construction of personalized 3D-printed models of patients' thyroids. Figure 1 shows a flow chart for establishing a personalized 3D-printed model for thyroids of patients. Figure 2 shows the personalized 3D-printed model printing device for thyroids of patients. Figure 3 shows the software interface for the establishment of a personalized 3D-printed model for thyroid patients. The interface shown is detailed in the video. Figure 4 shows the finished product of the personalized 3D-printed model of thyroids of patients. It shows different anatomical levels and states of the same patient's 3D model. On the left is the thyroid surgery area after muscle removal. On the right is the thyroid surgery area wrapped by sternocleidomastoid muscle. Figure 5 shows the case of a thyroid cancer patient for whom a complete 3D-printed model of the thyroid region was constructed through enhanced CT before operation. A is the coronal section, B is the transverse section, and C is the sagittal section of the patient's CT scan. D shows the 3D model built and printed based on CT. Based on CT, the transverse section of each CT scan is superposed to establish a 3D model. Compared with traditional CT, it is more stereoscopic and intuitive, and can be observed by 360° rotation.
Figure 1: The flow chart for establishing a personalized 3D-printed model for thyroid cancer patients. Please click here to view a larger version of this figure.
Figure 2: The personalized 3D-printed model device for thyroid cancer patients. Please click here to view a larger version of this figure.
Figure 3: The software interface for the establishment of a personalized 3D-printed model for thyroid cancer patients. The interface shown is detailed in the video. Please click here to view a larger version of this figure.
Figure 4: The finished product of the personalized 3D-printed model of thyroid cancer patients (the same model on the left and right part). On the left is the thyroid surgery area after muscle removal. On the right is the thyroid surgery area wrapped by sternocleidomastoid muscle. Please click here to view a larger version of this figure.
Figure 5: The case of a thyroid cancer patient who completed a 3D-printed model of the thyroid region through enhanced CT before operation. A is the coronal section of the patient's CT scan. B is the transverse section of the patient's CT scan. C is the sagittal section of the patient's CT scan. D shows the 3D model built and printed based on the CT scan. Based on CT, the transverse section of each CT scan is superposed to establish a 3D model. Compared with traditional CT, it is more stereoscopic and intuitive, and can be observed by 360° rotation. Please click here to view a larger version of this figure.
Supplemental File 1: Production and package of each model of custom 3D-printed full color thyroid models. Please click here to download this File.
Supplemental Table S1: Technical specifications of the color multi-material 3D printer. Please click here to download this File.
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Discussion
Ultrasound may be the only preoperative imaging procedure for most patients undergoing thyroid surgery15. However, a few well-differentiated cases may suffer from advanced diseases, which invade the surrounding tissues or organs and hinder the operation16. This model may be more suitable for patients with far-advanced thyroid cancer. When the disease progresses, additional CT scanning is helpful for further diagnosis. This model is based on CT scanning, which provides more anatomical and morphological information than the currently accessible batch-produced phantom of the thyroid. It can also clearly show the relationship between the thyroid tumor and the thyroid, as well as the relationship between the thyroid tumor and the surrounding tissues.
The resulting model can be used to predict major structural changes and malformations before surgery. In clinical practice, it greatly improves the efficiency of personalized surgical evaluation by doctors for different patients. The experience of surgeons showed that this model reduced the unpredictability of surgery and shortened the operation time. The significance of this model is to improve the prognosis of patients by providing sufficient information about the patient's own anatomical structure and variation and better understand the postoperative results, including complications that may be related to the natural process of surgery, and making a real thyroid phantom that reflects the CT-based anatomical structure.
In addition, making a 3D-printed thyroid cancer model can help patients better understand their health-related problems, and can help doctors to propose the best treatment plan. Previous studies showed that using 3D-printed models in medical education improved the effect of education17,18,19. A study used 3D printing technology to help teach the classification of acetabular fractures, as these complex bone anatomical structures require accurate surgical planning and confirmation17. A previous study used a 3D-printed half-pelvis for preoperative planning and achieved positive results by training inexperienced surgeons18. Another study used 3D-printed cleft lip and palate models as teaching aids, which can provide a better understanding of different patient scenarios19. For patients with thyroid cancer, 3D-printed models of patients before surgery may help the patients better understand what their surgery entails. In addition, this model also increased the interest of inexperienced clinicians in thyroid diseases, which helped clinician self-education before explaining the condition and procedure to patients to improve the quality of treatment and surgery planning.
We used a questionnaire to evaluate the usefulness of personalized 3D-printed thyroid models. We asked the patients how they felt about using 3D-printed thyroid models. The patients showed the highest scores in "understanding the disease" (71.7%), followed by "overall satisfaction" (17.0%), "understanding the surgery" (11.3%), and "worthless" (0%). These results showed that 3D modeling technology may be valuable for anatomy education. Showing the positional relationship between the tumor and the thyroid gland may be the greatest advantage of this 3D-printed model.
The time required to produce 3D-printed models, which includes modeling and printing time, is one of the main limitations, even though 3D printing has been integrated into modern medical practice. The design process for the pulmonary artery replication model took 8 h, while the printing process took 97 h and 14 min. Therefore, even though numerous studies on patient-specific (i.e., personalized) modeling techniques have been conducted for various anatomical sites or purposes (such as surgical guidelines or clinical training)20,21,22,23, their value in the clinical setting has only been demonstrated in a few studies16,24,25. In this regard, the advantage of this model was that we could reduce the time for creating personalized 3D models. Our model of the thyroid took only 3 h to build and 8 h to print.
A limitation of this study is that the model was based on the head and neck CT scan of thyroid cancer patients participating in this study, which incur additional costs. At the same time, 3D-printed models also incur additional costs. Therefore, in future research, patient-specific personalized printing models can be created for unique patient cases containing the individual thyroid and surrounding tissue information, which can be used to explain the procedures tailored to each patient and the benefits of this 3D model. In addition, the additional costs that patients need to pay should also be considered. This cost must be weighed against the actual benefits of the model and the additional costs that patients pay.
In conclusion, a new method of establishing a personalized 3D-printed model for the preoperative evaluation of thyroid surgery has been proposed, which is conducive to preoperative discussion and reduces the difficulty of thyroid surgery.
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Disclosures
The authors declare no conflicts of interest.
Acknowledgments
This study was supported by the health Committee of Sichuan Province (Grant No.20PJ061), the National Natural Science Foundation of China (Grant No.32101188), and the General Project of Science and Technology Department of Sichuan Province (Grant No. 2021YFS0102), China.
Materials
| Name | Company | Catalog Number | Comments |
| 3D color printer | Zhuhai Sina 3D Technology Co | J300PLUS | Function support: automatic optimized placement, automatic model typesetting, automatic generation support, real-time layered edge cutting and printing, slice export, custom color thickness, custom placement / scaling, man hour evaluation, material consumption evaluation, print status monitoring, material remaining display, changing materials and colors, managing work queues, full / semi enclosed printing, automatic detection of model interference, layer preview, automatic pause of ink shortage, power failure to resume printing Automatic cleaning nozzle, automatic channel adaptation, ink change, automatic cleaning pipeline, follow-up laying. Range of optional materials: RGD series transparent molding materials, RGD series opaque molding materials, FLX series soft molding materials, ABS like series molding materials, high temperature resistant molding materials, Med series molding materials (first-class medical record certification), ordinary supporting materials, water-soluble supporting materials. |
| Mimics 21.0 software | Materialise, Belgium | DICOM data processing |
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