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 Table of Contents  
ORIGINAL ARTICLE
Year : 2021  |  Volume : 12  |  Issue : 4  |  Page : 180-185

Simulated three-dimensional printing printed polyamide based PA2200 immovable device for cancer patients undergoing radiotherapy


1 Department of Radiation Oncology, Narayana Multispecialty Hospital; Division of Medical Physics, Faculty of Life Sciences, JSS Academy of Higher Education and Research, Mysuru, Karnataka, India
2 Department of Biotechnology and Bioinformatics, Faculty of Life Sciences, JSS Academy of Higher Education and Research, Mysuru, Karnataka, India
3 Division of Molecular Biology, Faculty of Life Sciences, JSS Academy of Higher Education and Research, Mysuru, Karnataka, India
4 Division of Medical Physics, Faculty of Life Sciences, JSS Academy of Higher Education and Research, Mysuru, Karnataka, India

Date of Submission31-Aug-2021
Date of Decision10-Sep-2021
Date of Acceptance22-Sep-2021
Date of Web Publication17-Nov-2021

Correspondence Address:
Dr. Shanmukhappa B Kaginelli
Division of Medical Physics, Faculty of Life Sciences, JSS Academy of Higher Education and Research, Mysuru, Karnataka
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jrcr.jrcr_28_21

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  Abstract 


Background: Radiotherapy is one of the most effective treatments for cancer. However, delivering an optimal dosage of radiation to the patients is always challenging due to the movements of the patient during treatment. Immobilization devices are typically used to minimize patient movement. Aims: The current work has been carried out to investigate the effectiveness of Three-dimensional printing (3D) printing to create patient-specific immobilization devices in comparison to traditional devices. Earlier studies have reported the advantages of 3D printed materials in the form of phantoms included improved patient experience and comfort over traditional methods. Further, high levels of accuracy between immobilizer and patient, reproducibility, and similar beam attenuation properties were better achieved compared to conventional or thermoformed immobilizers. Methods: The additive manufacturing process, however, is considered time-consuming as it requires time to print the desired shape. In the current study, polyamide-based PA 2200 which is biocompatible was used as source material for printing the customized Immobilize devices for radiotherapy. Results: Computer-aided designing (CAD) was used to design following the computer tomography scan of patients. The design was fed to the 3D printer for further processing. Conclusions: The mechanical properties of materials are important to receive the geometrical requirement that fits every patient. We used PA 2200, which is more biocompatible compared to other materials to produce phantoms using the system-generated design of the patient geometry. Further, phantoms produced did not show much deviation in radio fractionation when compared to the thermoplastic molds.

Keywords: Additive manufacturing, immobilization, PA 2200, phantoms, three-dimensional printing


How to cite this article:
Rajesh R, Gopenath T S, Basalingappa KM, Kaginelli SB. Simulated three-dimensional printing printed polyamide based PA2200 immovable device for cancer patients undergoing radiotherapy. J Radiat Cancer Res 2021;12:180-5

How to cite this URL:
Rajesh R, Gopenath T S, Basalingappa KM, Kaginelli SB. Simulated three-dimensional printing printed polyamide based PA2200 immovable device for cancer patients undergoing radiotherapy. J Radiat Cancer Res [serial online] 2021 [cited 2022 Jan 21];12:180-5. Available from: https://www.journalrcr.org/text.asp?2021/12/4/180/330595




  Introduction Top


Radiation therapy or radiotherapy is one of the most relied cancer treatments that uses high doses of radiation to kill cancer cells and shrink tumors. Radiotherapy can be effective and depends on certain important criteria like the type of cancer, size of the tumor, location of the tumor, age of the patient, relative distance to important organs within the body, etc. Since radiations can scatter to other parts of the body, which might induce radiation-induced side effects, conventional Plaster of Paris (POP) was used as an immobilizing agent since long, which could save patients from the scattering of radiation to healthy parts. Preparation of POP materials is labor intense, cumbersome, and takes hours together, which is quite inconvenient for patients. Then came the era of thermoplastic sheets or orifit cast materials, which has uniqueness of taking the shape of the body contour of patients. These thermoplastic sheets are dipped in hot water bath at 60°C at which the sheets start to melt and are immediately placed on the required body site of the patient before it comes to room temperature and the body structure is acquired within this time. However, it is found to be a difficult task to acquire true body shape or acquiring tailor-made body shape. Further, reproducibility is a greater challenge with conventional immobilization methodologies.

Three-dimensional printing (3D) has become widely used technology nowadays both in the industrial and medical fields.[1] It offers wide variety of flexibility in its usage. As like in other medical specialties, 3D printing or additive manufacturing technology is briskly taking its prime role of customization (tailor made) as per the requirement of patients.[2] Additive manufacturing techniques are being explored to create patient-specific shields and immobilize devices for patients during radiation therapy. The medical field has witnessed an enormous advancement in rapid prototyping and computer-aided designing (CAD), which has led to the fabrication of 3D models to assist in several services such as implantology,[3] orthopedics, surgical planning.[4],[5] 3D printing is considered as one of such powerful additive manufacturing processes that helps in radiation therapy.[6],[7] In general 3D printing uses scanning, designing, and printing. Scanning is performed with the help of special cameras while designing is accomplished with the help of computer-aided design software CAD and printing with a 3D printer. In the current scenario, we used computer tomography (CT) for scanning, contouring workstation for designing and a 3D printer for printing. Hospitals can have potential benefits both in terms of accuracy and in terms of cost. Speaking about the materials used to print the immobilize devices, several studies have addressed the issues regarding the selection of the right material that does not interfere with the treatment. Here, we used the polyamide-based PA 2200 which is found to be biocompatible. Further, it is a cost-efficient general-purpose material suitable for a variety of applications, including functional prototypes and qualified series production parts from the industry. However, its use in radiation therapy in India is minimal. Therefore, we attempted to create patient-specific head-and-neck molds with PA 2200 using a 3D printer. Here, we describe the materials used to create phantoms directly from a patient's CT scan, without involving the patient to print the required immobilize devices.


  Methods Top


In general, patients are diagnosed in the oncology department and decided for radiotherapy. Under conventional treatment practices, mold/cast is prepared in the mold room and the patient is taken to CT simulation for Tumor marker/CT isocentre marker placement. The preparatory phase is quite extensive as the thermoplastic materials used are heated to a temperature of 60°C under which, the sheets begin to show their elastic nature. Immediately the sheets are placed on the specific organ of the patients that require radiotherapy. The thermoplastic sheet takes the shape of the organ and begins to set in as the temperature drops to room temperature. During the entire process, the patients are expected to lay still as any minor movements might affect the shape of the mold. In the case of 3D printing, the patient directly goes for CT scanning which is quite faster. Based on the scanning output, computer simulation is carried out during which the images are fed into contouring station where the exact shape of body contours are drawn by technologist as per requirement. After CT simulation, scanning, and finalization of contour, either they can start 3D printing with tumor isocentre placement independently or true CT/Planning Isocentre marker might be implanted with the guidance of the physician so that Isocentre shift from the Physician for the 1st day execution can be avoided. Later, the simulated mold is directly fed into the 3D printer which prints the simulated mold using a biocompatible material such as PA2200 used in this study [Figure 1].
Figure 1: Flowchart of the method adopted. On the left, conventional method of preparing patients with thermoplastic materials is displayed. On the right, current method, adopted using PA2200 in combination with three-dimensional printing printing is displayed

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Treatment planning system

Treatment planning system (TPS) or treatment planning process generally is planned using computer algorithms to determine the best parameters based on every individual's disease, which includes, in this case, dosage of radiation, duration, dose fractionation, attenuation, patient positioning, and machine settings. Reference images and other relevant data generated in the system are used to set up further planning, following verifications. Precisely clinicians then follow the final output of this process over several weeks.

Software used for simulation

Computerized TPS is used in practical intensity-modulated radiation therapy (IMRT) treatment-plan optimization based on the creation of a joint objective function that promotes dose to the target volume and penalizes dose delivery elsewhere, paying special attention to certain volumes-at-risk. In practice, the value of certain starting parameters (the volume objective relative weights) are guessed and overall plan optimization via repeated iterations are achieved. CMS Xio (version-4.71) Elekta Instrument AB Stockholm, P O Box 7593, Kungstensgtan 18, SE-103 93 Stocholm, Elekta's Xio has been used for precision plans and smooth workflows [Figure 2]. The software is embedded with automation tools, advanced dose calculation, easy integration, and a high degree of flexibility. Xio's comprehensive planning workflow tools provide fast contouring, fusion, virtual sim, planning, and review tools in one.
Figure 2: Computerized treatment planning system using Elekta Xio Version 4.71. Contouring was carried out for a real-time patient. The pictures above depict contouring (a-c). The final version of the cast (d) is shown which is sent to the three-dimensional printing printer for mask printing

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Molding (casting) Material

Polyamide-based PA 2200 was used in the current study to mold immovable device for 3D printing [Figure 3]. PA 2200 is found to possess high strength and stiffness, excellent long-term constant behavior and importantly biocompatible according to EN ISO 10993-1.
Figure 3: Polyamide-based PA 2200 was selected in the current study to create molds for three-dimensional printing. It is a white powder, which can be casted to any shape when exposed to optimal temperature. This product is both food grade and biocompatible and therefore does not lead to any skin related issues when used on patients

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Three-dimensional printing tool

3D printing or otherwise called as Additive Manufacturing (AM) tool gives us wide variety of possibilities. There is much history in the development of 3D printing technology. In broad aspects, it involves scanning, designing, and printing. Scanning involves in obtaining 3D images to a printable format.


  Results Top


Three-dimensional printing

The current study emphasizes the importance of additive manufacturing, in particular 3D printing in radiotherapy. Only after 2014, 3D printing gained momentum, especially in the field of clinical investigation and treatment.[8] Earlier, 3D printing technology was a predominantly rapid prototyping technology, which has now shifted toward an end-use manufacturing technology. Availability of different compatible materials is one of the key factors that has played a vital role in the creation of immobilization devices.

PA 2200 cast

PA 2200, as mentioned above is a polyamide-based powder used to cast (immobilization devices) in the current study. This material is well known for usage due to its food-grade quality. Typical applications of the material are fully functional plastic parts of the highest quality. Although PA 2200 is widely used for cosmetic purposes, it has never been tried in radiotherapy at least in India. This study suggests that immobilized casts can be 3D printed using PA 2200, replacing the conventional POP and also the thermoplastic materials that are being used with great difficulty in achieving precision and patient-specific treatment plans [Figure 4].
Figure 4: Conventional thermoplastic immovable device is shown (a). The patients are required to lay still and the thermoplastic materials after reaching 60°C are placed on the targeted region to acquire the shape of the targeted organ. (b) A Three-dimensional printing printed immovable device produced with PA 2200 poly-amide after designing in Elekta Xio Version 4.71 software and three-dimensional printing printed. The immovable device is easily produced following a computer tomography scan of the patient. This minimizes the problems of patient movement, which normally is a part of conventional immobilization techniques

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Comparison of positional variation between conventional and three-dimensional printed immobilization phantoms

To compare the efficiency of the PA 2200 masks with the conventional thermoplastic masks, head phantoms were used for treatment. A dose of 2MU of radiation using 6MV X-ray beams were used to compare the radiation fractionation. The results suggest that the PA 2200 shows no remarkable deviation even after a month when compared to the conventional thermoplastic materials [Table 1].
Table 1: Comparison of radiation fractionation between the thermoplastic immovable device and 3D printed polyamide 2200 head phantoms

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  Discussion Top


Radiotherapy plays a significant role in the management and treatment of cancer. However, providing the radiation precisely is a huge challenge, which includes several factors. Treatment relies on accurate positional delivery. Usage of immobilization devices was the beginning of precision radiotherapy. Earlier practices involved creating an immovable device with materials such as POP, which was soon replaced by thermoplastic materials. Though thermoplastic materials are still being used and have provided with better therapy, preparation of immovable devices is still a laborious process. It includes treating the thermoplastic materials with an optimal temperature during which the materials begin to expose the elasticity. However, once the temperature drops down, the materials start to harden. This available timeframe is quite small between which the material is to be placed on the patient and to be more precise, on the desired organ and the material is allowed to take the shape of the selected organ. However, minor movements either of the organs or even by the patients lead to issues in radiation doses reaching nontarget areas. Recent technological advancement in the field of additive manufacturing has almost answered the previous issues faced during conventional methods, which is now more oriented toward patient-specific strategies.[9] Modern radiotherapy is challenged by several limitations such as the physical movement of patients resulting in different doses of radiation reaching targeted and nontargeted regions.

Creating a digital patient geometry is a prerequisite to produce a patient-specific immobilization device using CT, magnetic resonance imaging, optical 3D scanning and more manual CAD methods.[10],[11] The current study is based on the CT scan of patients. High-quality optical scanners could be better options compared to CT scans, but the provision of using those high-quality optical scanners could be costly affair. While CT scanning is still followed in several studies or practices, further research is required to evaluate and quantify an optimal method for digitizing patient data based on which, immobilization devices can be developed that are safe for humans.

Following the scan images of the patient, the workflow requires a digital design of patient-specific immobilization device to be developed.[12] In the current study, practical IMRT treatment-plan optimization was carried, paying special attention to certain volumes at risk. CMS Xio (version-4.71) Elekta's Xio has been used for precise plans and smooth workflows. The software is embedded with automation tools, advanced dose calculation, easy integration, and a high degree of flexibility.

The last stage of the technological flow is 3D printing of an immobilization device or mold. The final product of the printed mold was evaluated for defects and suitability for radiotherapy. It is to be noticed that, though printing might be carried out using the same printer and material belonging to the same manufacturer, it might lead to variation in densities of the final product. This might lead to the difference in radiation fractionation compared to conventional materials produced without a 3D printer. Although software's designs a patient-specific immobilizing phantom and the 3D printer prints the mold precisely, it is to be understood that these devices fall short of their utility without proper clinical interventions by medical physicists, radiotherapists, and oncologists, and at certain times, they fall short as they do not exactly replicate patients. Further, these fabricated phantoms might be very time-consuming and costly due to the use of specialized materials. Our experiment using head phantoms, however, showed no much deviation in radiation fractionation for almost a month, suggesting that the material used is greatly suitable for radiation therapy. However, it requires validation when used over real patients.

Additive manufacturing (AM) in clinical applications has taken a leap, commonly used in radiotherapy. 3D printing is the most commonly used technology in the field of AM and is being widely explored in radiotherapy.[13],[14] The technique aims at creating patient-specific immobilization devices. With the recent increase in radiotherapy 3D printing, a likely trend towards greater integration of the same in radiotherapy is resulting in the precision of treatment.[15] However, recently there seems to be a trend of identifying better materials at relatively less time-consuming and costly. This is especially true with 3D printing applications designed for patient-specific anatomy, which may require printed devices that possess patient-specific configurable arrangements or are disposable.


  Conclusions Top


As radiotherapy is proving to be one of the effective treatment processes of cancer, additive manufacturing is equally catching up its position in the field of clinical intervention. Parallel to the developments in AM, modern materials have almost replaced conventional thermoplastics. The mechanical properties of materials are important to receive the geometrical requirement that fits every patient. We used PA 2200, which is more biocompatible compared to other materials to produce phantoms using the system-generated design of the patient geometry. Further, phantoms produced did not show much deviation in radio fractionation when compared to the thermoplastic molds. This is a step closer to replace conventional thermoplastics with better compatible materials, which can be printed using a 3D printer, unlike involving the patients throughout the process of creating phantoms, in earlier procedures. The next important step would be to use these phantoms on real-time patients and validate their efficacy.

Acknowledgment

The authors wish to express their profound gratitude to the Management of JSS Academy of Higher Education and Research, Mysuru and Narayana Multispecialty Hospital, Mysuru for their support in carrying out this original work of research.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

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