Thermoplastic Three Dimensional bolus used in radiotherapy

Abstract

The present invention relates to a 3D bolus. The 3D bolus of the present invention is a 3D bolus 3D printed by a melt additive manufacturing method using a thermoplastic filament, wherein the thermoplastic filament comprises one or more types selected from the group consisting of PLA (Polylactic acid), TPU (Thermoplastic polyurethane), PETG (Polyethylene terephthalate glycol-modified), and HIPS (High Impact Polystyrene), and may have a thickness of 1.5 cm or less.

Description

Technology Field

[0001] The present invention relates to a thermoplastic 3D bolus used in radiation therapy according to embodiments of the invention. Background Technology

[0003] One method for effectively treating cancer involves irradiating a target with high-energy radiation to deliver the maximum radiation dose to a specific depth. The build-up effect is defined as the deep dose at which the maximum dose resulting from radiation irradiation of 400 kV or higher reaches an arbitrary depth; in the treatment of superficial cancer using high-energy photon beams, boluses are utilized to ensure accurate dose delivery and increase the dose to the target. A bolus is an auxiliary device used in radiation therapy; it is a flexible synthetic gel form that can be attached to the patient's body surface and is composed of tissue-equivalent materials that possess mass density and relative electron density similar to soft tissue. Commonly used in clinical practice include Superflab and Super-Flex bolus (Radiation Products Design Inc., USA), while the silicon-based CLEANBOLUS (Paprica Lab., Republic of Korea) has recently been developed. However, in the case of body surfaces that are irregular or highly curved, it is difficult to achieve complete adhesion of the bolus, which can lead to the formation of air gaps. This affects the dose distribution within the target volume and the maximum dose depth (Dmax) within the tumor, acting as a negative factor in the efficient treatment of cancer. To overcome these limitations, research is being conducted on fabricating patient-specific boluses using 3D printers. While 3D printing technology offers the advantages of allowing consideration of physical properties such as low density and high biocompatibility of the bolus, as well as the ability to fabricate them as patients-specifically, most studies involve printing with plastic materials that lack flexibility, leading to reports of various problems such as air gaps caused by breathing during treatment and skin dysesthesia.

[0004] delete Prior art literature

[65535] (1) P. Mantada, R. Mendricky and J. Safka, MM Sci. J.5, 2004(2017).(2) M. Whitaker, Ann. R. Coll. Surg. Engl. 96, 228 (2014).(3) K. Fujimoto et al., Phys. Med. 38, 1(2017). The problem to be solved

[0005] In related technology fields, boluses are used to enhance precise dose delivery and skin protection during the treatment of superficial cancer using high-energy photon beams. However, existing commercial boluses have limitations in that they create air pockets due to the difficulty of achieving complete adhesion to the human body surface.

[0006] Accordingly, the present invention designs flexible thermoplastic filaments such as PLA (Polylactic acid), TPU (Thermoplastic polyurethane), PETG (Polyethylene terephthalate glycol-modified), and HIPS (High Impact Polystyrene) that can be printed with a 3D (three-dimensional) printer, and combinations thereof, to produce 3D boluses of various thicknesses for radiation therapy effective in reducing the tumor dose distribution by reducing the air layer on the patient's body surface, and provides a 3D (Three Dimensional) boluse that is clinically feasible and custom-designed to fit the patient's body shape through performance comparison verification with existing boluses used in clinical practice by actual measurement using a medical linear accelerator.

[0007] However, the problems that the present invention aims to solve are not limited to those mentioned above, and other unmentioned problems will be clearly understood by those skilled in the art from the description below. means of solving the problem

[0009] According to one embodiment, the 3D bolus is a 3D bolus 3D printed by a melt additive manufacturing method using a thermoplastic filament, wherein the thermoplastic filament comprises one or more types selected from the group consisting of PLA (Polylactic acid), TPU (Thermoplastic polyurethane), PETG (Polyethylene terephthalate glycol-modified), and HIPS (High Impact Polystyrene), and may have a thickness of 1.5 cm or less.

[0010] According to one embodiment, the 3D bolus has an effective atomic number of 5.70 to 6.82 and a solid density (g / cm³). 3 It may be ) 1.03 to 1.24, melting point (mp) 146 ℃ to 200 ℃, and elongation at break (Mpa) 20 to 800.

[0011] According to one embodiment, the maximum dose depth of the 3D bolus is measured by placing the 3D bolus on the surface of a water phantom located at a distance of 100 cm from the source, and the maximum dose depth for a 6 MV photon beam is 1.0 cm to 1.1 cm, the maximum dose depth for a 10 MV photon beam is 2.4 cm to 2.6 cm, and the maximum dose depth for a 15 MV photon beam is 1.5 cm to 3 cm.

[0012] According to one embodiment, the maximum dose depth in the 15 MV photon beam of the 3D bolus may be 2.4 cm to 2.9 cm when the thickness of the 3D bolus is 0.5 cm, 1.9 cm to 2.6 cm when the thickness of the 3D bolus is 1.0 cm, and 1.5 cm to 2.0 cm when the thickness of the 3D bolus is 1.5 cm.

[0013] According to one embodiment, the thermoplastic filament has a thickness of 0.2 mm to 2 mm, the molecular weight (Mw) of the polymer constituting the thermoplastic filament is 60,000 Da to 500,000 Da, the PLA (Polylactic acid) comprises crystalline or semicrystalline PLA and amorphous PLA, and the ratio (w / w) of the crystalline or semicrystalline PLA to the amorphous PLA may be 20:1 to 2.5.

[0014] According to one embodiment, the thermoplastic filament may further comprise 1% to 20% by weight of PP (Polypropylene), PC (Polycarbonate), ABS (Acrylonitrile butadiene styrene copolymer), and nylon in the 3D bolus. Effects of the invention

[0016] The present invention can provide a 3D bolus that reduces foreign body sensation in patients and adheres to the body surface, enabling precise dose distribution and delivery within a planned volume target by using flexible thermoplastic filaments such as PLA (Polylactic acid), TPU (Thermoplastic polyurethane), PETG (Polyethylene terephthalate glycol-modified), and HIPS (High Impact Polystyrene) that can be printed by fused deposition modeling (FDM).

[0017] The present invention can provide a 3D bolus that enables a higher level of radiation therapy by fabricating a patient-specific bolus using FDM 3D printing or the like and applying it to the application site, such as head and neck cancer, breast cancer, or skin cancer. Brief explanation of the drawing

[0019] FIG. 1 shows images of boluses made of PLA, TPU, PETG, and HIPS according to one embodiment, with thicknesses of 0.5 cm, 1.0 cm, and 1.5 cm. FIG. 2 shows energy fluence spectra through PRIMO software according to one embodiment, with (a) 6 MV, (b) 10 MV, and (c) 15 MV. FIG. 3 is a schematic diagram of the irradiation depth (left) and measurement setup (right) of a photon beam using a bolus according to one embodiment. FIGS. 4a and 4b show images of an acrylic support fabricated to stably position a bolus on the surface of a water phantom according to one embodiment. FIG. 5 shows the percentage of depth dose for 6 MV and 15 MV photon beams in an open field according to one embodiment. FIG. 6 shows, according to one embodiment, (a) a comparison of deep dose percentages of a 0.5 cm bolus and a 3D printing bolus for a 6 MV beam, (b) a comparison of deep dose percentages of a 0.5 cm bolus and a 3D printing bolus for a 15 MV beam, (c) a comparison of deep dose percentages of a 1.0 cm bolus and a 3D printing bolus for a 15 MV beam, and (d) a comparison of deep dose percentages of a 1.5 cm bolus and a 3D printing bolus for a 15 MV beam. Specific details for implementing the invention

[0020] Hereinafter, the 3D bolus of the present invention and its applications will be described in detail with reference to the embodiments and drawings. However, the present invention is not limited to these embodiments and drawings.

[0022] According to one embodiment, the 3D bolus of the present invention may be 3D printed using a melt additive method with a thermoplastic filament. According to one embodiment, the thermoplastic filament is melted and 3D printed using a melt additive method, which reduces foreign body sensation and adheres to the body surface, enabling precise dose distribution and delivery within a planned volume. Additionally, it has flexibility, can be manufactured to fit the patient, and can reduce the air gap between the human body and the bolus.

[0024] According to one embodiment, the thermoplastic filament may include one or more types selected from the group consisting of PLA (Polylactic acid), TPU (Thermoplastic polyurethane), PETG (Polyethyene terephthalate glycol-modified), and HIPS (High Impact Polystyrene).

[0026] According to one embodiment, the molecular weight (Mw) of PLA (Polylactic acid), TPU (Thermoplastic polyurethane), PETG (Polyethyene terephthalate glycol-modified), and HIPS (High Impact Polystyrene) may be 60,000 Da to 500,000 Da; 80,000 Da to 500,000 Da; 90,000 Da to 500,000 Da; 100,000 Da to 500,000 Da; or 200,000 Da to 300,000 Da. By applying the mentioned molecular weights, a 3D bolus that can be used as a flexible and highly mechanically effective dose-raising bolus can be provided by 3D printing using the Fused Deposition Modeling (FDM) method.

[0028] According to one embodiment, the thermoplastic filament may have a thickness of 0.2 mm to 2 mm; 0.2 mm to 1.8 mm; 0.2 mm to 1.5 mm; 0.2 mm to 1.0 mm; or 0.2 mm to 0.8 mm. According to one embodiment, the PLA (Polylactic acid) may include crystalline or semicrystalline PLA and amorphous PLA. For example, the ratio (w / w) of the crystalline or semicrystalline PLA to the amorphous PLA may be 20:1 to 2.5; 20:1 to 2; or 20:1 to 1.5. This allows the amorphous PLA to be dispersed in the dispersed phase of the continuous phase of the crystalline or semicrystalline PLA, thereby improving mechanical properties and the accuracy of dose distribution and delivery.

[0030] According to one embodiment, in a 3D printing process using a melt additive method, a thermoplastic filament may be melted by increasing the temperature to 40°C to 300°C; 60°C to 290°C; 100°C to 280°C; 150°C to 290°C; 180°C to 290°C; 200°C to 290°C; or 260°C to 280°C, and a printed layer may be formed. According to one embodiment, the printed layer may be cooled in any manner to form at least a partially solidified layer. For example, at least a partially solidified layer may be formed by exposure to room temperature or ambient conditions for a predetermined period.

[0032] According to one embodiment, the thickness of the 3D bolus may be 2.0 cm or less; 1.5 cm or less; 1.0 cm or less; 0.5 cm or less; 0.1 cm to 2.0 cm; 0.5 cm to 2.0 cm; or 0.5 cm to 1.5 cm. By applying the mentioned thickness range, the bolus can be provided to reduce the error in the maximum dose depth, thereby increasing accurate dose delivery to the target and skin protection effects.

[0034] According to one embodiment, the 3D bolus may have an effective atomic number of 5.70 to 7.10; 6.64 to 7.10; or 6.82 to 7.10. According to one embodiment, the solid density (g / cm³) of the 3D bolus 3 ) may be 1.03 to 1.24; 1.21 to 1.24; or 1.27 to 1.24. According to one embodiment, the melting point (mp) of the 3D bolus may be 146 ℃ to 260 ℃; 146 ℃ to 200 ℃; 150 ℃ to 200 ℃; or 150 ℃ to 180 ℃; or 170 ℃ to 180 ℃. According to one embodiment, the elongation at break (Mpa) of the 3D bolus may be 20 to 800; 55 to 800; 83 to 800; 200 to 800; 500 to 800; or 600 to 800. The above elongation at break is related to the ISO 1798 standard. By applying physical properties and mechanical characteristics such as the mentioned effective atomic number, solid density, melting point, and elongation at break, it is possible to provide a bolus capable of precise dose distribution and delivery, which enhances accurate dose delivery to a target and skin protection effects, through a 3D printing process using a melt additive method.

[0036] According to one embodiment, the thermoplastic filament may further comprise one or more types selected from the group consisting of PP (Polypropylene), PC (Polycarbonate), ABS (Acrylonitrile butadiene styrene copolymer), and Nylon, or all of these, in order to control precise dose distribution and delivery while improving flexibility and mechanical properties. Their molecular weights (Mw) may be 60,000 Da to 500,000 Da; 80,000 Da to 500,000 Da; 90,000 Da to 500,000 Da; 100,000 Da to 500,000 Da; or 200,000 Da to 300,000 Da, respectively. These may comprise 1 wt% to 20 wt%; 1 wt% to 15 wt%; 2 wt% to 10 wt% of the 3D bolus; Alternatively, it may be included in an amount of 5% to 8% by weight. When mixed, they may be composed of equal amounts. For example, PP (Polypropylene) (e.g., C3H6) has a solid density (g / cm³). 3 It can provide a 3D bolus with a molecular weight of 0.90, a melting point (mp) of 160 °C, and an effective atomic number of 5.44. For example, ABS (Acrylonitrile butadiene styrene copolymer) (e.g., (C8H8-C4H6-C3H3N)n) has a solid density (g / cm³). 3 A 3D bolus can be provided with a molecular weight of 1.04, a melting point (mp) of 200 °C, and an effective atomic number of 5.76. For example, nylon (e.g., C 10 H2O(CO)2(NH)2) has a solid density (g / cm³) 3A 3D bolus can be provided with a molecular weight of 1.52, a melting point (mp) of 269 °C, and an effective atomic number of 6.12. For example, PC (Polycarbonate) (e.g., C 16 H 18 O5) is the solid density (g / cm³) 3 A 3D bolus with a value of 1.30, a melting point (mp) of 265 °C, and an effective atomic number of 6.44 can be provided.

[0038] According to one embodiment, the maximum dose depth of the 3D bolus was measured by applying the 100 MU standard according to the experimental system, medical linear accelerator, Blue Phantom 2 water phantom, and International Atomic Energy Agency task report-398 practice code according to FIG. 3, FIG. 4a and FIG. 4b, and positioning the bolus at a distance of 100 cm from the linear accelerator head.

[0040] According to one embodiment, the maximum dose depth of the 3D bolus in a 6 MV photon beam may be 1.0 cm to 1.1 cm. According to one embodiment, the maximum dose depth of the 3D bolus in a 15 MV photon beam may be 1.3 cm to 2.9 cm; 2.4 cm to 2.9 cm; or 1.3 cm to 2.0 cm.

[0041] For example, when the thickness of the 3D bolus is 0.5 cm, the maximum dose depth in a 6 MV photon beam may be 1.0 cm to 1.1 cm.

[0042] For example, when the thickness of the 3D bolus is 0.5 cm, the maximum dose depth in a 15 MV photon beam may be 2.4 cm to 2.9 cm.

[0043] For example, if the thickness of the above 3D bolus is 1.0 cm, it may be 1.9 cm to 2.6 cm.

[0044] For example, if the thickness of the 3D bolus is 1.5 cm, it may be 1.5 cm to 2.0 cm. That is, the 3D bolus can adjust the maximum dose depth according to its thickness, and can deliver an accurate dose to tumors within the body. In addition, as energy increases, penetration power becomes stronger, which increases the percentage of deep dose and can increase the maximum dose depth.

[0046] According to one embodiment, when the same measurement conditions are applied to the 3D bolus (e.g., FIG. 3), the average error range of the maximum dose depth point of the commercial bolus Superflab is about 0.13 cm or less, so the maximum dose depth points of the 3D bolus and the commercial bolus Superflab are similar and can provide a consistent trend of deep dose percentage.

[0048] According to one embodiment, the 3D bolus may have an air gap between the skin and the bolus of 0.3 cm or less; 0.2 cm or less; 0.1 cm or less; or 0.08 cm or less. The air gap between the skin and the bolus has a significant effect on the dose distribution during radiation therapy, and can be fabricated to fit an irregular skin surface using 3D printing with a flexible thermoplastic filament, and can have flexibility and adhesion to ensure maximum contact between the body contour and the bolus.

[0050] Examples

[0051] Production of 3D bolus

[0052] The 3D bolus was manufactured using a 3D printing machine with a process temperature, i.e., a nozzle temperature (Nizzle temperature) of ≤250℃, and a model of the CREALITY Ender-3 V2.

[0053] That is, thermoplastic materials that can be 3D printed to replace a bolus composed of tissue-equivalent material were selected, and the physical properties of PLA (Polylactic acid), TPU (Thermoplastic polyurethane), PETG (Polyethyene terephthalate glycol-modified), and HIPS (High Impact Polystyrene), which were selected considering physical properties and mechanical properties such as effective atomic number, density, melting point, and elongation (ISO1798; elongation at break), are shown in Table 1.

[0055] Physical property PLA TPU PETG HIPS Chemical formula C3H4O2 C4H4O4 C 10 H8O4 C8H8 Solid density(g / cm 3 ) 1.24 1.21 1.27 1.03 Effective atomic number (Z eff ) 6.82 7.10 6.64 5.70 Elongation at break(Mpa) 20 800 83 55

[0056] The bolus for each material has an area of ​​15 x 15 cm 2 The prototypes were designed with thicknesses of 0.5 cm, 1.0 cm, and 1.5 cm, and the 3D printer model used for printing the prototypes was Ender-3 V2 (Creality 3D Technology Co., Ltd., China). In this case, considering the density and uniformity of the bolus, the infill was set to 100% during printing, and the prototype boluses produced for each variable are shown in Fig. 1.

[0057] Physical property evaluation

[0058] Radiation dose characteristics regarding variations in the maximum dose depth point for photon beams used in radiation therapy were evaluated for four 3D printed filament materials applicable to boluses using GATE (Geant4 Application for Tomographic Emission) version 9.0, a Monte Carlo simulation tool. The linear accelerator model simulated for the simulation was Clinac iX (Varian Medical Systems, USA), and the photon energy spectra were set to 6 MV, 10 MV, and 15 MV, which are clinically used, calculated using PRIMO software as shown in Figure 2. PRIMO is software built based on the PENOPE, PENEASY, and PENEASYLINAC codes and is capable of performing Monte Carlo simulations of medical linear accelerators. During the experiment, the distance between the source and the phantom was 100 cm, and the irradiation field size was 10 x 10 cm. 2 It was measured by setting it to .

[0060] The medical linear accelerator model used to measure the maximum dose depth within the Percent Depth Dose (PDD), a performance indicator of the bolus, was the Clinac 21iX (Varian Medical Systems, USA); it was set to 6 MV and 15 MV photon energies, which are primarily applied in radiation therapy, and the dimensions were 675 x 645 x 560 mm 3 Blue Phantom of standard specifications 2 (IBA Dosimetry, Germany) A water phantom was used. In addition, a cylindrical ion ionization chamber CC13 (IBA Dosimetry, Germany), suitable for measuring surface and accumulation region doses of high-energy photons, was used, with a cavity radius, length, and volume of 0.30 cm⁻¹. 3 , 1.58 cm 3 , 0.13 cm 3In accordance with the International Atomic Energy Agency (IAEA) Task Report-398 Code of Practice, based on 100 MU, the irradiation field at the maximum underwater dose depth is 10 x 10 cm. 2 It was set to [value], and the bolus was positioned at a distance of 100 cm from the linear accelerator head. The overall experimental structure is as shown in Fig. 3.

[0062] As shown in FIGS. 4a and 4b, an acrylic support was fabricated to stably position the bolus on the surface of the water phantom, measuring 15 x 15 cm. 2 A bolus of size 12 x 12 cm is placed in the center of the support where the photon beam is irradiated. 2 A void space of that size was created to minimize the effect of the dose delivered to the ion ionization chamber.

[0064] The theoretically reported Open PDD of the Clinac iX medical linear accelerator is 1.6±0.15 and 2.9±0.15 cm for photon beam energies of 6 and 15 MV, respectively. The Open PDD measured at the Clinac 21iX linear accelerator used in this study was confirmed to be 1.5 cm and 2.9 cm, as shown in Figure 5, with an average error of less than 2%.

[0066] Using the Monte Carlo simulation tool GATE 9.0, radiation dose characteristics regarding variations in maximum dose depth points for 6 MV, 10 MV, and 15 MV photon beams were evaluated, and four types of thermoplastic filaments that can be printed using the FDM method—PLA, TPU, PETG, and HIPS—were fabricated at 0.5 cm, 1.0 cm, and 1.5 cm, and their maximum dose depths were compared with those of the commercial bolus Superflab.

[0068] result

[0069] The maximum dose depth of each sample is shown in Tables 2 to 6.

[0070] Table 2 shows the maximum dose depth of a 0.5 cm GATE simulation and a 3D-printed bolus for 6 MV irradiation conditions.

[0071] Table 3 shows the maximum dose depth of a 0.5 cm GATE simulation and a 3D-printed bolus for 15 MV irradiation conditions.

[0072] Table 4 shows the maximum dose depth of a 1.0 cm GATE simulation and a 3D-printed bolus for 15 MV irradiation conditions.

[0073] Table 5 shows the maximum dose depth of a 1.5 cm GATE simulation and a 3D-printed bolus for 15 MV irradiation conditions.

[0074] Table 6 shows the maximum dose depths of 0.5 cm, 1.0 cm, 1.5 cm, and 2.0 cm GATE simulations and 3D printed boluses for 10 MV irradiation conditions.

[0075] For 6 MV photons, as shown in Table 2, the maximum dose depth was found to be 1.2 cm when using a commercial Superflab bolus with a thickness of 0.5 cm, and the maximum dose depth for 0.5 cm thick PLA, TPU, HIPS, and PETG materials was confirmed to be 1.1 for each material. For 15 MV photons, as shown in Tables 3, 4, and 5, the maximum dose depth was found to be 2.5 cm when using a commercial Superflab bolus with a thickness of 0.5 cm, and the maximum dose depths for 0.5 cm thick PLA, TPU, HIPS, and PETG materials were 2.5, 2.5, 2.4, and 2.6 cm, respectively. When using a 1.0 cm Superflab, the maximum dose depth was found to be 1.9 cm, and the maximum dose depths for PLA, TPU, HIPS, and PETG materials of the same thickness were measured to be 1.9, 2.2, 2.1, and 2.4 cm, respectively. Additionally, when using a 1.5 cm Superflab, the maximum dose depth was found to be 1.6 cm, and the maximum dose depths for PLA, TPU, HIPS, and PETG materials of 1.5 cm thickness were confirmed to be 1.7, 1.5, 1.6, and 1.8 cm, respectively. Furthermore, it was confirmed that the maximum dose depth is controlled according to the thickness.

[0077] Materials Thickness (cm) Superflab PLA TPU PETG HIPS GATE - 1.1 1.1 1.0 1.1 Varian 21iX 1.2 1.1 1.1 1.1 1.1

[0078] Materials Thickness (cm) Superflab PLA TPU PETG HIPS GATE - 2.8 2.9 2.7 2.7 Varian 21iX 2.5 2.5 2.5 2.4 2.6

[0079] Materials Thickness (cm) Superflab PLA TPU PETG HIPS GATE - 2.0 2.2 2.1 2.6 Varian 21iX 1.9 1.9 2.2 2.1 2.4

[0080] Materials Thickness (cm) Superflab PLA TPU PETG HIPS GATE - 1.7 1.6 1.3 2.0 Varian 21iX 1.6 1.7 1.5 1.6 1.8

[0081] Materials (10 MV) GATEThickness (cm) PLA TPU PETG HIPS 0.5 1.8 1.9 1.8 1.9 1.0 1.3 1.5 1.3 1.7 1.5 0.7 0.8 0.4 0.8 2.0 0.4 0.4 0.2 0.4

[0082] The present invention enables the delivery of an accurate dose to a tumor in the body by adjusting the maximum dose depth using a thermoplastic filament used in 3D printing, and reduces air pockets by fabricating it to fit the irregular skin surface. In the present invention, the bolus fabricated by the FDM method exhibits stronger penetration power as energy increases, similar to the commercial bolus Superflab, and the maximum dose depth increases as the percentage of deep dose increases. Additionally, as shown in Fig. 6, it exhibited a consistent trend of moving away from the surface of a water phantom, confirming its potential for use as a dose-increasing bolus.

[0083] In the present invention, for 6 MV photons, when a commercial Superflab bolus with a thickness of 0.5 cm was used, the maximum dose depth and the respective errors for PLA, TPU, HIPS, and PETG materials with a thickness of 0.5 cm were confirmed to be 0.04 cm, 0.08 cm, 0.08 cm, and 0.01 cm, respectively. For 15 MV photons, when a commercial Superflab bolus with a thickness of 0.5 cm was used, the maximum dose depth and the errors for PLA, TPU, HIPS, and PETG materials with a thickness of 0.5 cm were confirmed to be 0.03 cm, 0.03 cm, 0.11 cm, and 0.10 cm, respectively. When a 1.0 cm Superflab was used, the maximum dose depth and the errors for PLA, TPU, HIPS, and PETG materials with a thickness of 1.0 cm were measured to be 0.01 cm, 0.29 cm, 0.26 cm, and 0.52 cm, respectively. In addition, when using a 1.5 cm Superflab, the maximum dose depth and the error with 1.5 cm thick PLA, TPU, HIPS, and PETG materials were confirmed to be 0.04 cm, 0.09 cm, 0.01 cm, and 0.21 cm, respectively.

[0085] In this invention, an experiment was conducted with an air gap of 5 cm between the water phantom and the support for dose measurement. When a photon beam reaches the bolus, low-energy secondary electrons are added to the photon beam through photon interaction; these electrons affect the surface dose and can extend to the maximum dose depth. However, the air gap formed as the bolus moves a certain distance away from the phantom surface reduces the influence of electrons formed in the bolus due to particle partial attenuation. Therefore, if the thickness of the bolus and the area of ​​the air gap are kept equal for the photon beam, the maximum dose depth shifts to the phantom surface.

[0087] In this invention, flexible thermoplastic filaments such as PLA, TPU, PETG, and HIPS were fabricated into boluses of 0.5, 1.0, and 1.5 cm and compared with the commercial bolus Superflab for variations in the dose rise region. This was verified by GATE simulation. The average error between the commercial bolus Superflab and the thermoplastic filaments was 0.13 cm, with a maximum dose depth (D max It was confirmed that ) was similar and the potential for use as a dose-increasing bolus was confirmed through the consistent trend of the Percent depth dose (PDD).

[0089] The embodiments of the present invention described above are disclosed for illustrative purposes only, and those skilled in the art with ordinary knowledge of the present invention may make various modifications, changes, and additions within the spirit and scope of the present invention, and such modifications, changes, and additions should be considered to fall within the scope of the following claims.

Claims

Claim 1 A 3D bolus 3D printed by a melt additive manufacturing method using a thermoplastic filament, wherein the thermoplastic filament comprises one or more types selected from the group consisting of PLA (Polylactic acid), TPU (Thermoplastic polyurethane), PETG (Polyethylene terephthalate glycol-modified), and HIPS (High Impact Polystyrene), has a thickness of 1.5 cm or less, and the 3D bolus has an effective atomic number of 5.70 to 6.82 and a solid density (g / cm³). 3 A 3D (Three Dimensional) bolus having a molecular weight of 1.03 to 1.24, a melting point (mp) of 146 °C to 200 °C, and an elongation at break (Mpa) of 83 to 800, wherein the thermoplastic filament has a thickness of 0.2 mm to 2 mm, the molecular weight (Mw) of the polymer constituting the thermoplastic filament is 60,000 Da to 500,000 Da, the PLA (Polylactic acid) comprises crystalline or semicrystalline PLA and amorphous PLA, and the ratio (w / w) of the crystalline or semicrystalline PLA to the amorphous PLA is 20:1 to 1.

5. Claim 2 delete Claim 3 A 3D bolus according to claim 1, wherein the maximum dose depth of the 3D bolus is measured by placing the 3D bolus on the surface of a water phantom located at a distance of 100 cm from the source, and the maximum dose depth is 1.0 cm to 1.1 cm for a 6 MV photon beam, the maximum dose depth is 2.4 cm to 2.6 cm for a 10 MV photon beam, and the maximum dose depth is 1.5 cm to 3 cm for a 15 MV photon beam. Claim 4 A 3D bolus according to claim 1, wherein the maximum dose depth in a 15 MV photon beam of the 3D bolus is 2.4 cm to 2.9 cm when the thickness of the 3D bolus is 0.5 cm, 1.9 cm to 2.6 cm when the thickness of the 3D bolus is 1.0 cm, and 1.5 cm to 2.0 cm when the thickness of the 3D bolus is 1.5 cm. Claim 5 delete Claim 6 A 3D bolus according to claim 1, wherein the thermoplastic filament further comprises 1% to 20% by weight of PP (Polypropylene), PC (Polycarbonate), ABS (Acrylonitrile butadiene styrene copolymer), and nylon.

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