Characterization of 3D printing techniques: Toward patient specific quality assurance spine-shaped phantom for stereotactic body radiation therapy

3D-Printed Polymeric Biomaterials for Health Applications

3D printing, also known as additive manufacturing, holds immense potential for rapid prototyping and customized production of functional health-related devices. With advancements in polymer chemistry and biomedical engineering, polymeric biomaterials have become integral to 3D-printed biomedical applications. However, there still exists a bottleneck in the compatibility of polymeric biomaterials with different 3D printing methods, as well as intrinsic challenges such as limited printing resolution and rates. Therefore, this review aims to introduce the current state-of-the-art in 3D-printed functional polymeric health-related devices. It begins with an overview of the landscape of 3D printing techniques, followed by an examination of commonly used polymeric biomaterials. Subsequently, examples of 3D-printed biomedical devices are provided and classified into categories such as biosensors, bioactuators, soft robotics, energy storage systems, self-powered devices, and data science in bioplotting. The emphasis is on exploring the current capabilities of 3D printing in manufacturing polymeric biomaterials into desired geometries that facilitate device functionality and studying the reasons for material choice. Finally, an outlook with challenges and possible improvements in the near future is presented, projecting the contribution of general 3D printing and polymeric biomaterials in the field of healthcare.

Fabrication of 3D printed head phantom using plaster mixed with polylactic acid powder for patient-specific QA in intensity-modulated radiotherapy

This study aimed to fabricate a heterogeneous phantom replicating the commercial Rando phantom by mixing plaster powder and polylactic acid (PLA) powder. Producing a heterogeneous phantom using Plaster and PLA is cheaper because it can be easily obtained in the commercial market. Additionally, patient-specific Quality Assurance can be easily performed because the phantom can be produced based on the patient's CT image. PLA has been well studied in the field of radiation therapy and was found to be safe and effective. To match the mean Hounsfield unit (HU) values of the Rando phantom, the bone tissue was changed using plaster and 0-35% PLA powder until an appropriate HU value was obtained, and soft tissue was changed using the PLA infill value until an appropriate HU value was obtained. Bone tissue (200 HU or higher), soft issue (- 500 to 200 HU), and air cavity (less than - 500 HU) were modeled based on the HU values on the computed tomography (CT) image. The bone tissue was modeled as a cavity, and after three-dimensional (3D) printing, a solution containing a mixture of plaster and PLA powder was poured. To evaluate the bone implementation of the phantom obtained by the mixture of plaster and PLA powder, the HU profile of the CT images of the 3D-printed phantom using only PLA and the Rando phantom printed using only PLA was evaluated. The mean HU value for soft tissue in the Rando phantom (- 22.5 HU) showed the greatest similarity to the result obtained with an infill value of 82% (- 20 HU). The mean HU value for bone tissue (669 HU) showed the greatest similarity to the value obtained with 15% PLA powder (680 HU). Thus, for the phantom composed of plaster mixed with PLA powder, soft tissue was fabricated using a 3D printer with an infill value of 82%, and bone tissue was fabricated with a mixture containing 15% PLA powder. In the HU profile, this phantom showed a mean difference of 61 HU for soft tissue and 109 HU for bone tissue in comparison with the Rando phantom. The ratio of PLA powder and plaster can be adjusted to achieve an HU value similar to bone tissue. A simple combination of PLA powder and plaster enabled the creation of a custom phantom that showed similarities to the Rando phantom in both soft tissue and bone tissue.

3D printing methods for radiological anthropomorphic phantoms

Three dimensional (3D) printing technology has been widely evaluated for the fabrication of various anthropomorphic phantoms during the last couple of decades. The demand for such high quality phantoms is constantly rising and gaining an ever-increasing interest. Although, in a short time 3D printing technology provided phantoms with more realistic features when compared to the previous conventional methods, there are still several aspects to be explored. One of these aspects is the further development of the current 3D printing methods and software devoted to radiological applications. The current 3D printing software and methods usually employ 3D models, while the direct association of medical images with the 3D printing process is needed in order to provide results of higher accuracy and closer to the actual tissues' texture. Another aspect of high importance is the development of suitable printing materials. Ideally, those materials should be able to emulate the entire range of soft and bone tissues, while still matching the human's anatomy. Five types of 3D printing methods have been mainly investigated so far: (a) solidification of photo-curing materials; (b) deposition of melted plastic materials; (c) printing paper-based phantoms with radiopaque ink; (d) melting or binding plastic powder; and (e) bio-printing. From the first and second category, polymer jetting technology and fused filament fabrication (FFF), also known as fused deposition modelling (FDM), are the most promising technologies for the fulfilment of the requirements of realistic and radiologically equivalent anthropomorphic phantoms. Another interesting approach is the fabrication of radiopaque paper-based phantoms using inkjet printers. Although, this may provide phantoms of high accuracy, the utilized materials during the fabrication process are restricted to inks doped with various contrast materials. A similar condition applies to the polymer jetting technology, which despite being quite fast and very accurate, the utilized materials are restricted to those capable of polymerization. The situation is better for FFF/FDM 3D printers, since various compositions of plastic filaments with external substances can be produced conveniently. Although, the speed and accuracy of this 3D printing method are lower compared to the others, the relatively low-cost, constantly improving resolution, sufficient printing volume and plethora of materials are quite promising for the creation of human size heterogeneous phantoms and their adaptation to the treatment procedures of patients in the current health systems.

Low cost multifunctional 3D printed image quality and dose verification phantom for an image-guided radiotherapy system

Purpose

Image-guided radiation therapy (IGRT) is used to precisely deliver radiation to a tumour to reduce the possible damage to the surrounding normal tissues. Clinics use various quality assurance (QA) equipment to ensure that the performance of the IGRT system meets the international standards set for the system. The objective of this study was to develop a low-cost and multipurpose module for evaluating image quality and dose.

Methods

A multipurpose phantom was designed to meet the clinical requirements of high accuracy, easy setup, and calibration. The outer shell of the phantom was fabricated using acrylic. Three dimensional (3D) printing technology was used to fabricate inner slabs with the characteristics of high spatial resolution, low-contrast detectability, a 3D grid, and liquid-filled uniformity. All materials were compatible with magnetic resonance (MR). Computed tomography (CT) simulator and linear accelerator (LINAC) modules were developed and validated.

Results

The uniformity slab filled with water is ideal for the assessment of Hounsfield units, whereas that filled with wax is suitable for consistency checks. The high-spatial-resolution slab enables measurements with a resolution up to 5 lp/cm. The low-contrast detectability slab contains rods of 5 different sizes that can be clearly visualised. These components meet the American College of Radiology (ACR) standards for QA of CT simulators and LINACs.

Conclusions

The multifunctional phantom module meets the ACR recommended QA guidelines and is suitable for both LINACs and CT-sim. Further measurements in an MR simulator and an MR linear accelerator (MR-LINAC) will be arranged in the future.

DEVELOPMENT OF A THREE-DIMENSIONAL-PRINTED HEART MODEL REPLICATING THE ELASTICITY, TEAR RESISTANCE, AND HARDNESS OF PIG HEART USING AGILUS AND TANGO

This study proposes a manufacturing method for reproducing some physical properties of the heart by comparing the elasticity, tear resistance, and hardness of a pig heart and three-dimensional printing materials, Agilus and Tango. A Digital Force Gauge was used to analyze elastic modulus and tear resistance, whereas a Shore A hardness meter was used to measure hardness. Agilus and Tango had 10 and 5 times higher elasticity, respectively, 2 and 4 times higher tear resistance, and a higher Shore A hardness than the pig heart. In summary, the pig heart had a more similar elasticity and Shore A hardness than the Tango sample, whereas more tear resistance was similar to the Agilus sample. Therefore, we proposed elasticity and tear resistance equations that can be used to build a heart model and a conversion table for heart fabrication at various thicknesses.

COMPARISON OF PULMONARY NODULE DETECTION, READING TIMES AND PATIENT DOSES OF ULTRA-LOW DOSE CT, STANDARD DOSE CT AND DIGITAL RADIOGRAPHY

The purpose of the present work was to evaluate performance in pulmonary nodule detection, reading times and patient doses for ultra-low dose computed tomography (ULD-CT), standard dose chest CT (SD-CT), and digital radiography (DR). Pulmonary nodules were simulated in an anthropomorphic lung phantom. Thirty cases, 18 with lesions (45 total lesions of 3-12 mm) and 12 without lesions were acquired for each imaging modality. Three radiologists interpreted the cases in a free-response study. Performance was assessed using the JAFROC figure-of-merit (FOM). Performance was not significantly different between ULD-CT and SD-CT (FOMs: 0.787 vs 0.814; ΔFOM: 0.03), but both CT techniques were superior to DR (FOM: 0.541; ΔFOM: 0.31 and 0.28). Overall, the CT modalities took longer time to interpret than DR. ULD chest CT may serve as an alternative to both SD-CT and conventional radiography, considerably reducing dose in the first case and improving diagnostic accuracy in the second.

Use of Three-Dimensional Printing in Modelling an Anatomical Structure with a High Computed Tomography Attenuation Value: A Feasibility Study

Introduction: Three-dimensional (3D) printing provides an opportunity to develop anthropomorphic computed tomography (CT) phantoms with anatomical and radiological features mimicking a range of patients’ conditions, thus allowing development of individualised, low dose scanning protocols. However, previous studies of 3D printing in CT phantom development could only create anatomical structures using potassium iodide with attenuation values up to 1200 HU which is insufficient to mimic the radiological features of some high attenuation structures such as cortical bone. This study aimed at investigating the feasibility of using 3D printing in modelling cortical bone with a non-iodinated material. Methods: This study had 2 stages. Stage 1 involved a vat photopolymerisation 3D printer to directly print cube phantoms with different percentage compositions of calcium phosphate (CP) and resin (approach 1), and approach 2 using a material extrusion 3D printer to develop a cube mould for infilling of the CP with hardener as the phantom. The approach able to create the cube phantom with the CT attenuation value close to that of a tibial mid-diaphysis cortex of a real patient, 1475±205 HU was employed to develop a tibial mid-diaphysis phantom. The mean CT numbers of the cube and tibia phantoms were measured and compared with that of the original CT dataset through unpaired t-test. Results: All phantoms were scanned by CT using a lower extremity scanning protocol. The moulding approach was selected to develop the tibia middiaphysis phantom with CT attenuation value, 1434±184 HU which was not statistically significantly different from the one of the original dataset (p = 0.721). Conclusion: This study demonstrates the feasibility to use the material extrusion 3D printer to create a tibial mid-diaphysis mould for infilling of the CP as an anthropomorphic CT phantom and the attenuation value of its cortex matches the real patient’s one.

Investigation of the effects of spinal surgical implants on radiotherapy dosimetry: A study of 3D printed phantoms

PURPOSE

The use of three-dimensional (3D) printing to develop custom phantoms for dosimetric studies in radiotherapy is increasing. The process allows production of phantoms designed to evaluated specific geometries, patients, or patient groups with a defining feature. The ability to print bone-equivalent phantoms has, however, proved challenging. The purpose of this work was to 3D print a series of three similar spine phantoms containing no surgical implants, implants made of titanium, and implants made of carbon fiber, for future dosimetric and imaging studies. Phantoms were evaluated for (a) tissue and bone equivalence, (b) geometric accuracy compared to design, and (c) similarity to one another.

METHODS

Sample blocks of PLA, HIPS, and StoneFil PLA-concrete with different infill densities were printed to evaluate tissue and bone equivalence. The samples were used to develop CT to physical (PD) and effective relative electron density (RED_eff ) conversion curves and define the settings for printing the phantoms. CT scans of the printed phantoms were obtained to assess the geometry and densities achieved. Mean distance to agreement (MDA) and DICE coefficient (DSC) values were calculated between contours defining the different materials, obtained from design and like phantom modules. HU values were used to determine PD and RED_eff and subsequently evaluate tissue and bone equivalence.

RESULTS

Sample objects showed linear relationships between HU and both PD and RED_eff for both PLA and StoneFil. The PD and RED_eff of the objects calculated using clinical CT conversion curves were not accurate and custom conversion curves were required. PLA printed with 90% infill density was found to have a PD of 1.11 ± 0.03 g.cm^-3 and RED_eff of 1.04 ± 0.02 and selected for tissue- equivalent phantom elements. StoneFil printed with 100% infill density showed a PD of 1.35 ± 0.03 g.cm^-3 and RED_eff of 1.24 ± 0.04 and was selected for bone-equivalent elements. Upon evaluation of the final phantoms, the PLA elements displayed PD in the range of 1.10 ± 0.03 g.cm^-3 -1.13 ± 0.03 g.cm^-3 and RED_eff in the range of 1.02 ± 0.03-1.06 ± 0.03. The StoneFil elements showed PD in the range of 1.43 ± 0.04 g.cm^-3 -1.46 ± 0.04 g.cm^-3 and RED_eff in the range of 1.31 ± 0.04-1.33 ± 0.04. The PLA phantom elements were shown to have MDA of ≤1.00 mm and DSC of ≥0.95 compared to design, and ≤0.48 mm and ≥0.91 compared like modules. The StoneFil elements displayed MDA values of ≤0.44 mm and DSC of ≥0.98 compared to design and ≤0.43 mm and ≥0.92 compared like modules.

CONCLUSIONS

Phantoms which were radiologically equivalent to tissue and bone were produced with a high level of similarity to design and even higher level of similarity of one another. When used in conjunction with the derived CT to PD or RED_eff conversion curves they are suitable for evaluating the effects of spinal surgical implants of varying material of construction.

Patient-Specific Quality Assurance Using a 3D-Printed Chest Phantom for Intraoperative Radiotherapy in Breast Cancer

This study aims to confirm the usefulness of patient-specific quality assurance (PSQA) using three-dimensional (3D)-printed phantoms in ensuring the stability of IORT and the precision of the treatment administered. In this study, five patient-specific chest phantoms were fabricated using a 3D printer such that they were dosimetrically equivalent to the chests of actual patients in terms of organ density and shape around the given target, where a spherical applicator was inserted for breast IORT treatment via the INTRABEAM™ system. Models of lungs and soft tissue were fabricated by applying infill ratios corresponding to the mean Hounsfield unit (HU) values calculated from CT scans of the patients. The two models were then assembled into one. A 3D-printed water-equivalent phantom was also fabricated to verify the vendor-provided depth dose curve. Pieces of an EBT3 film were inserted into the 3D-printed customized phantoms to measure the doses. A 10 Gy prescription dose based on the surface of the spherical applicator was delivered and measured through EBT3 films parallel and perpendicular to the axis of the beam. The shapes of the phantoms, CT values, and absorbed doses were compared between the expected and printed ones. The morphological agreement among the five patient-specific 3D chest phantoms was assessed. The mean differences in terms of HU between the patients and the phantoms was 2.2 HU for soft tissue and −26.2 HU for the lungs. The dose irradiated on the surface of the spherical applicator yielded a percent error of −2.16% ± 3.91% between the measured and prescribed doses. In a depth dose comparison using a 3D-printed water phantom, the uncertainty in the measurements based on the EBT3 film decreased as the depth increased beyond 5 mm, and a good agreement in terms of the absolute dose was noted between the EBT3 film and the vendor data. These results demonstrate the applicability of the 3D-printed chest phantom for PSQA in breast IORT. This enhanced precision offers new opportunities for advancements in IORT.

Assessment of Spinal Tumor Treatment Using Implanted 3D-Printed Vertebral Bodies with Robotic Stereotactic Radiotherapy

To investigate the feasibility and early efficacy of 3D-printed vertebral body implantation combined with robotic radiosurgery in the treatment of spinal tumors. This study included 14 patients with spinal tumors from December 2017 to June 2018. Before surgery, all patients were subjected to CT scan and 3D data of the corresponding vertebral segments were collected. Titanium alloy formed 3D-printed vertebral body implantation and robotic stereotactic radiotherapy were performed because of the risk of postoperative residual, high risk of recovery, or recurrence after surgery. The main outcomes included the remission of symptoms, vertebral body stability, robotic stereotactic surgical precision, and local tumor control. All patients received complete and successful combination therapy, and all healed primarily without complications. The error of the coverage accuracy for robotic radiosurgery was less than 0.5 mm, and the error of the rotation angle was less than 0.5°. The therapeutic toxicity was limited (mainly in grades 1–2), and adverse events were uncommon. The evaluation of vertebral body stability and histocompatibility for all patients met the postoperative clinical requirements. For patients with post spinal injury, the pain symptoms were reduced or disappeared (93%), and nerve function was improved or even recovered after treatment (100%). During our follow-up period, most tumors were locally well controlled (93%). 3D- printed vertebral body implantation combined with robotic radiosurgery may offer a new treatment of spinal tumors.

Chinese clinical trial registry: ChiCTR-ONN-17013946.

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With the development of 3D printing and robotic radiotherapy technology, the outcome of spinal tumors has been shown to have improving opportunities

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In this study, 14 patients with spinal tumor were treated by 3D printing vertebral body implantation combined with robotic radiotherapy, and the results showed that treatment could achieve requirements of spinal function perfectly and precisely kill the tumor

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3D printing vertebral body implantation combined with robotic stereotactic radiotherapy might be a treatment revolution for spinal tumors

What would you like to print? Students' opinions on the use of 3D printing technology in medicine

Background

Recent advances in 3D printing technology, and biomaterials are revolutionizing medicine. The beneficiaries of this technology are primarily patients, but also students of medical faculties. Taking into account that not all students have full, direct access to the latest advances in additive technologies, we surveyed their opinion on 3D printing and education in this area. The research aimed to determine what knowledge about the use of 3D printing technology in medicine, do students of medical faculties have.

Methods

The research was carried out in the form of a questionnaire among 430 students of the Medical University of Silesia in Katowice (Poland) representing various fields of medicine and health sciences. The questions included in the survey analyzed the knowledge of the respondents for 3D printing technology and the opportunities it creates in medicine.

Results

The results indicate that students do have knowledge about 3D printing obtained mainly from the internet. They would be happy to deepen their knowledge at specialized courses in this field. Students appreciated the value of 3D printing in order to obtain accurate anatomical models, helpful in learning. However, they do not consider the possibility of complete abandonment of human cadavers in the anatomy classes. Their knowledge includes basic information about current applications of 3D printing in medicine, but not in all areas. However, they have no ethical doubts regarding the use of 3D printing in any form. The vast majority of students deemed it necessary to incorporate information regarding 3D printing technology into the curriculum of different medical majors.

Conclusion

This research is the first of its kind, which allows for probing students' knowledge about the additive technologies in medicine. Medical education should be extended to include issues related to the use of 3D printing for medical applications.

Creation of an anthropomorphic CT head phantom for verification of image segmentation

Purpose

Many methods are available to segment structural magnetic resonance (MR) images of the brain into different tissue types. These have generally been developed for research purposes but there is some clinical use in the diagnosis of neurodegenerative diseases such as dementia. The potential exists for computed tomography (CT) segmentation to be used in place of MRI segmentation, but this will require a method to verify the accuracy of CT processing, particularly if algorithms developed for MR are used, as MR has notably greater tissue contrast.

Methods

To investigate these issues we have created a three‐dimensional (3D) printed brain with realistic Hounsfield unit (HU) values based on tissue maps segmented directly from an individual T1 MRI scan of a normal subject. Several T1 MRI scans of normal subjects from the ADNI database were segmented using SPM12 and used to create stereolithography files of different tissues for 3D printing. The attenuation properties of several material blends were investigated, and three suitable formulations were used to print an object expected to have realistic geometry and attenuation properties. A skull was simulated by coating the object with plaster of Paris impregnated bandages. Using two CT scanners, the realism of the phantom was assessed by the measurement of HU values, SPM12 segmentation and comparison with the source data used to create the phantom.

Results

Realistic relative HU values were measured although a subtraction of 60 was required to obtain equivalence with the expected values (gray matter 32.9–35.8 phantom, 29.9–34.2 literature). Segmentation of images acquired at different kVps/mAs showed excellent agreement with the source data (Dice Similarity Coefficient 0.79 for gray matter). The performance of two scanners with two segmentation methods was compared, with the scanners found to have similar performance and with one segmentation method clearly superior to the other.

Conclusion

The ability to use 3D printing to create a realistic (in terms of geometry and attenuation properties) head phantom has been demonstrated and used in an initial assessment of CT segmentation accuracy using freely available software developed for MRI.

A Systematic Review on 3D-Printed Imaging and Dosimetry Phantoms in Radiation Therapy

INTRODUCTION

Additive manufacturing or 3-dimensional printing has become a widespread technology with many applications in medicine. We have conducted a systematic review of its application in radiation oncology with a particular emphasis on the creation of phantoms for image quality assessment and radiation dosimetry. Traditionally used phantoms for quality assurance in radiotherapy are often constraint by simplified geometry and homogenous nature to perform imaging analysis or pretreatment dosimetric verification. Such phantoms are limited due to their ability in only representing the average human body, not only in proportion and radiation properties but also do not accommodate pathological features. These limiting factors restrict the patient-specific quality assurance process to verify image-guided positioning accuracy and/or dose accuracy in "water-like" condition.

METHODS AND RESULTS

English speaking manuscripts published since 2008 were searched in 5 databases (Google Scholar, Scopus, PubMed, IEEE Xplore, and Web of Science). A significant increase in publications over the 10 years was observed with imaging and dosimetry phantoms about the same total number (52 vs 50). Key features of additive manufacturing are the customization with creation of realistic pathology as well as the ability to vary density and as such contrast. Commonly used printing materials, such as polylactic acid, acrylonitrile butadiene styrene, high-impact polystyrene and many more, are utilized to achieve a wide range of achievable X-ray attenuation values from -1000 HU to 500 HU and higher. Not surprisingly, multimaterial printing using the polymer jetting technology is emerging as an important printing process with its ability to create heterogeneous phantoms for dosimetry in radiotherapy.

CONCLUSION

Given the flexibility and increasing availability and low cost of additive manufacturing, it can be expected that its applications for radiation medicine will continue to increase.

Development and validation of a bespoke phantom to test accuracy of Cobb angle measurements

INTRODUCTION

Adolescent idiopathic scoliosis (AIS) is a spinal deformity that causes the spine to bend laterally. Patients with AIS undergo frequent X-ray examinations to monitor the progression of the disorder by through the measurement of the Cobb angle. Frequent exposure of adolescents poses the risk of radiation-induced cancer. The aim of this research was to design and build a bespoke phantom representing a 10-year-old child with AIS to allow optimisation of imaging protocols for AIS assessment through the accuracy of Cobb angle measurements.

METHODS

Poly-methyl methacrylate (PMMA) and plaster of Paris (PoP) were used to represent human soft tissue and bone tissue, respectively, to construct a phantom exhibiting a 15° lateral curve of the spine. The phantom was validated by comparing the Hounsfield unit (HU) of its vertebrae with that of human and sheep. Additionally, comparisons of signal-to-noise ratio (SNR) to those from a commercially available phantom. An assessment of the accuracy of the radiographic assessment of the Cobb angle measurement was performed.

RESULTS

The HU of the PoP vertebrae was 628 (SD = 56), human vertebrae was 598 (SD = 79) and sheep vertebra was 605 (SD = 83). The SNR values of the two phantoms correlated strongly (r = 0.93 (p = 0.00)). The measured scoliosis angle was 14°.

CONCLUSION

The phantom has physical characteristics (in terms of spinal deformity) and radiological characteristics (in terms of HU and SNR values) of the spine of a 10-year-old child with AIS. This phantom has utility for the optimisation of x-ray imaging techniques in 10 year old children.

IMPLICATIONS FOR PRACTICE

A phantom to investigate new x-ray imaging techniques and technology in the assessment of scoliosis and to optimise currently used protocols.

Digital Light Processing Based Three-dimensional Printing for Medical Applications

An additive manufacturing technology based on projection light, digital light processing (DLP), three-dimensional (3D) printing, has been widely applied in the field of medical products production and development. The precision projection light, reflected by a digital micromirror device of million pixels instead of one focused point, provides this technology both printing accuracy and printing speed. In particular, this printing technology provides a relatively mild condition to cells due to its non-direct contact. This review introduces the DLP-based 3D printing technology and its applications in medicine, including precise medical devices, functionalized artificial tissues, and specific drug delivery systems. The products are particularly discussed for their significance in medicine. This review indicates that the DLP-based 3D printing technology provides a potential tool for biological research and clinical medicine. While, it is faced to the challenges of scale-up of its usage and waiting period of regulatory approval.

Repair of osteonecrosis of the femoral head : 3D printed Cervi cornus Colla deproteinized bone scaffolds

Background

Osteonecrosis of the femoral head (ONFH) is a common joint disease and a major cause of morbidity.

Objective

In this study Cervi cornus Colla (CCC) deproteinized bone scaffolds were designed and three dimensional (3D)-printed for the repair of ONFH in rats.

Material and methods

The CCC-deproteinized bone scaffolds were 3D-printed using polycaprolactone mixed with the CCC-deproteinized bone powder. The scaffolds were viewed under a scanning electron microscope and subjected to compression analysis. Osteoblasts were isolated from rats and coated onto the scaffolds. Cell proliferation assays were performed with the MTT (3‑[4,5-dimethylthiazole‑2]-2,5-diphenyltetrazolium bromide) kit from Promega. An ONFH was induced in rats and a CCC-deproteinized bone scaffold was implanted into the necrotic femoral head. General observations, X‑ray imaging, and pathological examination of the femoral head were performed to evaluate the treatment of ONFH in the rats.

Results

The scaffolds were porous with a mean pore diameter of 315.70 ± 41.52 nm and a porosity of 72.86 ± 5.45% and exhibited favorable mechanical properties and degradation. In vitro assays showed that osteoblasts accumulated in the pores and adhered to the scaffolds. The CCC-deproteinized bone scaffolds enhanced the proliferation of osteoblasts. The in vivo experiments revealed that the general observation score of rats in the CCC-scaffold implanted group was significantly higher than that in the control group. The X‑ray images showed significant alleviation of ONFH in the CCC-deproteinized bone scaffold implanted rats. The femoral heads of rats in the treatment group showed less destruction or ossification of cartilage cells, few bone cement lines, very little necrosis or irregularities on the cartilage surface and only a small amount of inflammatory cell infiltration in the medullary cavity.

Conclusion

These results suggest that CCC-deproteinized bone scaffold implants facilitated the repair of ONFH in rats. This research provides a new therapeutic approach for the repair of early and mid-term ONFH.

A modern mold room: Meshing 3D surface scanning, digital design, and 3D printing with bolus fabrication

Purpose

This case series represents an initial experience with implementing 3‐dimensional (3D) surface scanning, digital design, and 3D printing for bolus fabrication for patients with complex surface anatomy where traditional approaches are challenging.

Methods and Materials

For 10 patients requiring bolus in regions with complex contours, bolus was designed digitally from 3D surface scanning data or computed tomography (CT) images using either a treatment planning system or mesh editing software. Boluses were printed using a fused deposition modeling printer with polylactic acid. Quality assurance tests were performed for each printed bolus to verify density and shape.

Results

For 9 of 10 patients, digitally designed boluses were used for treatment with no issues. In 1 case, the bolus was not used because dosimetric requirements were met without the bolus. QA tests revealed that the bulk density was within 3% of the reference value for 9 of 12 prints, and with more judicious selection of print settings this could be increased. For these 9 prints, density uniformity was as good as or better than our traditional sheet bolus material. The average shape error of the pieces was less than 0.5 mm, and no issues with fit or comfort were encountered during use.

Conclusions

This study demonstrates that new technologies such as 3D surface scanning, digital design and 3D printing can be safely and effectively used to modernize bolus fabrication.

Dose perturbation by metallic biliary stent in external beam radiotherapy of pancreato-biliary cancers

This study aims to investigate dose perturbations caused by a metallic biliary stent (MBS) in patients undergoing external beam radiotherapy for cancers in the pancreato-biliary region. Four MBSs with nitinol mesh were examined in the EasyCube^® phantom including a custom stent holder fabricated by a 3D printer. For experimental models, three-dimensional conformal radiotherapy plans using a single anterior-posterior (AP) and four-field box (4FB) as well as volumetric modulated arc therapy (VMAT) plan were prepared to deliver the photon beam of 8 Gy to the stent holder. EBT3 film was used to measure dose distributions at four sides surrounding MBS. All MBSs in the AP beam demonstrated mean dose enhancements of 2.3-8.2% at the proximal, left, and right sides. Maximum dose enhancements of 12.3-19.5% appeared at regions surrounding the radiopaque markers. At the location distal to the source, there were mean dose reductions of - 3.6 to - 10.9% and minimum doses of - 11.1 to - 9.5%. The mean and maximum doses with the 4FB plan were in the ranges of - 0.1 to 3.6% and 6.7-14.9%, respectively. The VMAT produced mean doses of - 0.9 to 4.8% and maximum doses of 6.0-15.3%. Dose perturbations were observed with maximum and minimum spots near the stent surface. The use of multiple beams including parallel-opposed pairs reduced dose perturbations caused by the nitinol and radiopaque components within the stent. Special attention is required for patients in whom the radiopaque markers are closely located near critical structures or the target volume.

Characterization of a novel 3D printed patient specific phantom for quality assurance in cranial stereotactic radiosurgery applications

In single-isocenter stereotactic radiosurgery/radiotherapy (SRS/SRT) intracranial applications, multiple targets are being treated concurrently, often involving non-coplanar arcs, small photon beams and steep dose gradients. In search for more rigorous quality assurance protocols, this work presents and evaluates a novel methodology for patient-specific pre-treatment plan verification, utilizing 3D printing technology. In a patient's planning CT scan, the external contour and bone structures were segmented and 3D-printed using high-density bone-mimicking material. The resulting head phantom was filled with water while a film dosimetry insert was incorporated. Patient and phantom CT image series were fused and inspected for anatomical coherence. HUs and corresponding densities were compared in several anatomical regions within the head. Furthermore, the level of patient-to-phantom dosimetric equivalence was evaluated both computationally and experimentally. A single-isocenter multi-focal SRS treatment plan was prepared, while dose distributions were calculated on both CT image series, using identical calculation parameters. Phantom- and patient-derived dose distributions were compared in terms of isolines, DVHs, dose-volume metrics and 3D gamma index (GI) analysis. The phantom was treated as if the real patient and film measurements were compared against the patient-derived calculated dose distribution. Visual inspection of the fused CT images suggests excellent geometric similarity between phantom and patient, also confirmed using similarity indices. HUs and densities agreed within one standard deviation except for the skin (modeled as 'bone') and sinuses (water-filled). GI comparison between the calculated distributions resulted in passing rates better than 97% (1%/1 mm). DVHs and dose-volume metrics were also in satisfying agreement. In addition to serving as a feasibility proof-of-concept, experimental absolute film dosimetry verified the computational study results. GI passing rates were above 90%. Results of this work suggest that employing the presented methodology, patient-equivalent phantoms (except for the skin and sinuses areas) can be produced, enabling literally patient-specific pre-treatment plan verification in intracranial applications.

Development of an organ-specific insert phantom generated using a 3D printer for investigations of cardiac computed tomography protocols

INTRODUCTION

An ideal organ-specific insert phantom should be able to simulate the anatomical features with appropriate appearances in the resultant computed tomography (CT) images. This study investigated a 3D printing technology to develop a novel and cost-effective cardiac insert phantom derived from volumetric CT image datasets of anthropomorphic chest phantom.

METHODS

Cardiac insert volumes were segmented from CT image datasets, derived from an anthropomorphic chest phantom of Lungman N-01 (Kyoto Kagaku, Japan). These segmented datasets were converted to a virtual 3D-isosurface of heart-shaped shell, while two other removable inserts were included using computer-aided design (CAD) software program. This newly designed cardiac insert phantom was later printed by using a fused deposition modelling (FDM) process via a Creatbot DM Plus 3D printer. Then, several selected filling materials, such as contrast media, oil, water and jelly, were loaded into designated spaces in the 3D-printed phantom. The 3D-printed cardiac insert phantom was positioned within the anthropomorphic chest phantom and 30 repeated CT acquisitions performed using a multi-detector scanner at 120-kVp tube potential. Attenuation (Hounsfield Unit, HU) values were measured and compared to the image datasets of real-patient and Catphan® 500 phantom.

RESULTS

The output of the 3D-printed cardiac insert phantom was a solid acrylic plastic material, which was strong, light in weight and cost-effective. HU values of the filling materials were comparable to the image datasets of real-patient and Catphan® 500 phantom.

CONCLUSIONS

A novel and cost-effective cardiac insert phantom for anthropomorphic chest phantom was developed using volumetric CT image datasets with a 3D printer. Hence, this suggested the printing methodology could be applied to generate other phantoms for CT imaging studies.

Intrapatient study comparing 3D printed bolus versus standard vinyl gel sheet bolus for postmastectomy chest wall radiation therapy

PURPOSE

This patient study evaluated the use of 3-dimensional (3D) printed bolus for chest wall radiation therapy compared with standard sheet bolus with regard to accuracy of fit, surface dose measured in vivo, and efficiency of patient setup. By alternating bolus type over the course of therapy, each patient served as her own control.

METHODS AND MATERIALS

For 16 patients undergoing chest wall radiation therapy, a custom 5.0 mm thick bolus was designed based on the treatment planning computed tomography scan and 3D printed using polylactic acid. Cone beam computed tomography scanning was used to image and quantify the accuracy of fit of the 2 bolus types with regard to air gaps between the bolus and skin. As a quality assurance measure for the 3D printed bolus, optically stimulated luminescent dosimetry provided in vivo comparison of surface dose at 7 points on the chest wall. Durations of patient setup and image guidance were recorded and compared.

RESULTS

In 13 of 16 patients, the bolus was printed without user intervention, and the median print time was 12.6 hours. The accuracy of fit of the bolus to the chest wall was improved significantly relative to standard sheet bolus, with the frequency of air gaps 5 mm or greater reduced from 30% to 13% (P < .001) and maximum air gap dimension diminished from 0.5 ± 0.3 to 0.3 ± 0.3 mm on average. Surface dose was within 3% for both standard sheet and 3D printed bolus. On average, the use of 3D printed bolus reduced the setup time from 104 to 76 seconds.

CONCLUSIONS

This study demonstrates 3D printed bolus in postmastectomy radiation therapy improves fit of the bolus and reduces patient setup time marginally compared with standard vinyl gel sheet bolus. The time savings on patient setup must be weighed against the considerable time needed for the 3D printing process.