Biocompatible fiducial marker using multi-block copolymers
09662408 ยท 2017-05-30
Assignee
- Samsung Life Public Welfare Foundation (Seoul, KR)
- Research & Business Foundation Sungkyunkwan University (Suwon-si, KR)
Inventors
- Young Yih Han (Seoul, KR)
- Hee Chul Park (Seoul, KR)
- Doo Sung Lee (Gwacheon-si, KR)
- Jae Myoung Noh (Seoul, KR)
- Sang Hee Ahn (Seoul, KR)
- Hye Young Kim (Seoul, KR)
- Moon Soo Gil (Anyang-si, KR)
Cpc classification
International classification
Abstract
The present invention relates to a fiducial marker comprising barium sulfate (BaSO.sub.4), a solvent, and a polyethylene glycol-poly(aminourethaneurea) multi-block copolymer, as active ingredients. The fiducial marker of the present invention has an effect of significantly remedying disadvantages of image distortion and dose distortion, which are involved in the gold inner marker used in the conventional art. The fiducial marker of the present invention has very limited in vivo mobility, and thus the fiducial marker is maintained at the position at which it has been initially injected. Since the fiducial marker of the present invention is maintained in a sol or liquid state before in vivo injection, and transited into a gel or solid phase after in vivo injection, the injectability of the fiducial marker by an injector syringe is favorable, and the state of the fiducial marker can be controlled into a phase suitable to each site of the therapeutic target.
Claims
1. A fiducial marker, comprising: (i) barium sulfate (BaSO.sub.4); (ii) a solvent; and (iii) a polyethyleneglycol-poly(aminoureaurethane) multi-block copolymer, as active ingredients, wherein the content of the barium sulfate (BaSO.sub.4) is 10-20 wt %, wherein the content of the polyethyleneglycol-poly(aminoureaurethane) multi-block copolymer is 1-20 wt %, and wherein the polyethylene glycol-poly(aminoureaurethane) multi-block copolymer has a repeat unit represented by chemical formula 1 below: ##STR00002## wherein n1 is an integer of 7 to 50; n2 is an integer of 2 to 8; n3 is an integer of 1 to 10; and m is an integer of 2 to 6.
2. The fiducial marker of claim 1, wherein the polyethylene glycol-poly(aminoureaurethane) multi-block copolymer has a molecular weight of 15,000 g/mol to 25,000 g/mol.
3. The fiducial marker of claim 1, wherein in chemical formula 1, n2 is 6.
4. The fiducial marker of claim 1, wherein in chemical formula 1, n3 is 2.
5. The fiducial marker of claim 1, wherein the solvent is a buffer.
6. The fiducial marker of claim 5, wherein the buffer is buffered saline.
7. The fiducial marker of claim 1, wherein the fiducial marker is used to display the position of a diseased part in the body at the time of radiotherapy.
8. The fiducial marker of claim 1, wherein the polyethylene glycol-poly(aminoureaurethane) multi-block copolymer is degraded in vivo.
9. The fiducial marker of claim 1, wherein the fiducial marker is in an injection type in which the fiducial marker is injected into the body in a sol phase.
10. The fiducial marker of claim 1, wherein the fiducial marker is hardened in a gel phase in the body after in vivo injection.
11. The fiducial marker of claim 1, wherein the fiducial marker shows a 90% or more reduction in the degree of image distortion compared with a metal fiducial marker.
12. The fiducial marker of claim 1, wherein the fiducial marker shows a 11.26% or more reduction in the degree of dose distortion compared with a metal fiducial marker.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) The above and other objects, features, and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
(10) Hereinafter, the present invention will be described in detail with reference to examples. These examples are only for illustrating the present invention more specifically, and it will be apparent to those skilled in the art that the scope of the present invention is not limited by these examples.
EXAMPLES
Materials and Methods
(11) Materials
(12) Polyethylene glycols (PEG), 2-hydroxyethyl piperazine, 1,6-diisocyanato hexamethylene, dibutyltin dilaurate (DBTL), anhydrous chloroform, phosphate buffered saline (PBS), and barium sulfate (BaSO.sub.4) were obtained from Sigma-Aldrich (St. Louis, Mo., USA). Hydrochloric acid (HCl), sodium hydroxide (NaOH), and diethyl ether were obtained from Samchun Co. (Seoul, Korea).
(13) Preparation of Barium Sulfate (BaSO.sub.4) Markers
(14) Barium sulfate (BaSO.sub.4) markers were prepared based on the polyethyleneglycol-poly(aminoureaurethane) ([PEG-PAUU]x) block copolymer (C. T. Huynh, Q. V. Nguyen, S. W. Kang, D. S. Lee, Polymer 2012, 53, 4069), and the synthesis of the copolymer was performed according to the disclosure of literature (Cong Truc Huynh et al., Polymer 53, 2012, 4069-4075; Cong Truc Huynh et al., Macromolecules 2011, 44, 6629-6636). The barium sulfate (BaSO.sub.4) marker, which is an X-ray contrast agent, was prepared by diffusing and penetrating barium sulfate (BaSO.sub.4) in the synthesized [PEG-PAUU]x block copolymer. That is, the barium sulfate (BaSO.sub.4) marker was prepared by sequentially mixing the [PEG-PAUU]x block copolymer as a carrier, and phosphate buffered saline (PBS) as a solvent. First, the synthesized [PEG-PAUU]x block copolymer was dissolved in the phosphate buffered saline (PBS) to give 10 wt % under conditions of 20 C. and pH 6.0, to form a sol in a liquid phase, and then barium sulfate (BaSO.sub.4), which is an X-ray contrast, was added to the prepared sol to be dispersed in the sol. Two kinds of barium sulfate (BaSO.sub.4) markers having barium sulfate (BaSO.sub.4) contents of 10 wt % and 20 wt %, respectively, were prepared. The barium sulfate (BaSO.sub.4) marker having a barium sulfate (BaSO.sub.4) content of 10 wt % designated by B1 was differentiated from the barium sulfate (BaSO.sub.4) marker having a barium sulfate (BaSO.sub.4) content of 20 wt % designated by B2.
(15) In Vitro Sol-Gel Transition Measurement
(16) The sol-gel transition measurement was performed on the synthesized barium sulfate (BaSO.sub.4) markers B1 and B2 materials in a solution state, through a tube inversion method. The synthesized [PEG-PAUU]x block copolymer was adjusted to pH=1 using 5 N NaOH and 5 N HCl, and completely dissolved in phosphate buffered saline (PBS) for 5 h to give a concentration of 10 wt %. Then, the prepared polymer solution was again adjusted to pH=6.0 at 20 C. and then dispensed in 4 ml tubes. The barium sulfate (BaSO.sub.4) was added to the prepared [PEG-PAUU]x block copolymer solutions to give concentrations of 10 wt % (B1) and 20 wt % (B2), respectively, and then dispersed for 1 h using a sonicator (ULSSO TECH, Sonosmasher). Again, the respective tubes were adjusted to a desired pH value, and then stabilized at 2 C. for 12 h. The respective tubes were fixed to a temperature-adjustable water bath, and then the changes of the solutions depending on the temperature change were observed while the temperature was slowly raised from 0 C. to 90 C. The sol-gel transition measurement was conducted using a tube inversion method for 1 min at each temperature.
(17) Rheological Measurement
(18) A dynamic mechanical analyzer (Bohlin Rotational Rheometer) was used to determine the viscosity change of each barium sulfate (BaSO.sub.4) marker solution depending on the barium sulfate (BaSO.sub.4) concentration. Oscillation mode with controlled conditions of 0.4 Pa and 1 rad/s frequency was used. The variation of the viscosity was observed by loading the barium sulfate (BaSO.sub.4) marker solutions on 20-diameter plates, preparing samples with a gap of 250 mm, and then slowly increasing the temperature from 0 C. to 60 C.
(19) In Vivo Gel Formation and Degradation of Barium Sulfate (BaSO.sub.4)
(20) Male Spraque-Dawley (SD) rats (Hanlim Experimental Animal Laboratory, Seoul, Korea) were used for the in vivo experiments. The rats (5-6 weeks old, average body weight 200 g) were used, and managed in accordance with the National Institutes of Health (NIH) guide lines for the care and use of laboratory animals.
(21) In order to investigate the injectability through injection, in vivo gelation, and gel stability of the barium sulfate (BaSO.sub.4) markers, 200 l of B1 marker and B2 marker with pH 5.8 were injected subcutaneously into the back of the male SD rats. After the injection, the rats were sacrificed according to the time up to the maximum 4 months, and the gel morphology was observed. In order to investigate the in vivo degradation over time, the rats to which the barium sulfate (BaSO.sub.4) markers were injected were sacrificed according to the time, and the gel size was measured. In addition, the gel was freeze-dried, and then the weight of the remaining gel was calculated through comparison with the gel state at the time of initial injection, thereby analyzing biodegradability.
(22) Phantom
(23) In order to insert a cage housing mice into a phantom simulating the human stomach, the phantom was fabricated to have a similar size to the human stomach. The phantom with a size of 30 cm30 cm18 cm was fabricated using polymethacrylicacidmethyl (PMMA) (
(24) Mice
(25) A total of 40 BALB/C mice (5 weeks old) were experimented on a barium sulfate (BaSO.sub.4) 10 wt % marker (B1 marker) group and a barium sulfate (BaSO.sub.4) 10 wt % marker (B2 marker) group with 20 mice for each group. The barium sulfate (BaSO.sub.4) markers were subcutaneously injected into the back of the right leg using an injection syringe. The amounts of injection were 10 l ( 1.0 mm) and 20 l ( 2.0 mm), and the mice were differentiated by punching the ear.
(26) Optimal Image Conditions Values
(27) The cages housing anesthetized mice were located inside the phantom, and then imaged using image apparatuses installed at the linear accelerator for treatment in the order of cone-beam computed tomography (CBCT), an On-Board Imager, which is an X-ray orthogonal imaging system, and fluoroscopy. The variations of the markers were observed while eleven experiments were conducted every two weeks for five months. Bolus containing the markers were inserted into a solid phantom (270 cm180 cm180 cm) fabricated for intensity modulated radiation therapy, and then optimal image condition values for B1 marker and B2 marker were obtained. The sizes of the markers were 1.0 mm and 2.0 mm, which were smaller than 4 mm, the size of the commercialized gold marker. Cone-beam computed tomography (CBCT) was reconstituted with a slice thickness of 1.0 mm, and imaging was conducted in the anterior-posterior direction and lateral direction for OBI and fluoroscopy.
(28) Evaluation on Image Distortion and Dose Distortion
(29) In order to evaluate the degree of image distortion, a gold marker and a barium sulfate (BaSO.sub.4) marker were contained in the boluses, and then housed in the phantom cage, followed by computed tomography (CT) imaging for analysis. For analysis of image distortion, the degree of image distortion was evaluated by setting a region of interest (ROI) in the periphery of each of the markers to 2020 pixels (15.6 mm15.6 mm) and then analyzing the distribution of the histogram, excluding each marker itself.
(30) In order to investigate the degree of dose distortion in the proton therapy, Monte Carlo computer simulation made based on Geant 4 was conducted. The degrees of dose distortion of gold, stainless steel, titanium, and barium sulfate (BaSO.sub.4) were evaluated in the same conditions. Cylindrical markers of gold, stainless steel, titanium, and barium sulfate (BaSO.sub.4), which have the same size (diameter: 1 mm, length: 3 mm) as a gold marker (diameter: 1 mm, length: 3 mm) actually used in the radiotherapy, were fabricated, and a proton beam was allowed to pass through the respective markers to compare the degree of distortion therebetween. Each of the markers was located inside the virtual phantom of polymethacrylicacidmethyl (PMMA), having a similar size to the human abdomen such that the marker was located in two direction, parallel and perpendicular to the proton beam direction, and then the proton beam was allowed to pass therethrough to compare the degree of dose distortion through computer simulation.
(31) Results
(32) Barium Sulfate (BaSO.sub.4) Marker Images
(33) The barium sulfate (BaSO.sub.4) marker could be identified on cone-beam computed tomography (CBCT), On-Board Imager (OBI), and fluoroscopy images, and the degree of identification was verified based on the cone-beam computed tomography (CBCT) image. The identifiability of the barium sulfate (BaSO.sub.4) marker was high on the cone-beam computed tomography (CBCT) image, and it was verified that the marker was formed in an irregular shape but not a symmetric sphere shape.
(34) Eclipse (version 10.1), which is a commercialized radiotherapy planning system for imaging and analysis, was used. The differentiation on the cone-beam computed tomography (CBCT) image was conducted using naked eye differentiation and the line profile, so that the barium sulfate (BaSO.sub.4) marker was differentiated from the surrounding tissues using a profile value of 1000. In order to verify the degree of absorption, the maximum brightness intensity of the marker on the image was measured through conversion into gray scale and Hounsfield Unit (HU). As a result of measuring the variation degree of the 2 mm-sized marker of the barium sulfate (BaSO.sub.4) 20 wt % B2 marker, which is identifiable group on all the images, at the interval of two weeks, the brightness intensity value showed an increase trend over time in the gray scale and Hounsfield unit (HU) (
(35) For the On-Board Imager (OBI) and fluoroscopy, the identification of the marker was easier in the anterior-posterior direction rather than the lateral direction, and the identifiability was high in B2 marker having a higher barium sulfate (BaSO.sub.4) content and the 2 mm-sized marker (table 1 and
(36) TABLE-US-00001 TABLE 1 Identifiability High Low Barium sulfate (BaSO4) B2 B1 marker Size 2 mm 1 mm Gantry rotation 0 (Anterior- 90 Posterior) (Lateral) HU 1500> 1500<
(37) In order to quantitatively compare the size change of the barium sulfate (BaSO.sub.4), any six mice (B1 1 mm 1 animal, 2 mm 2 animals, B2 1 mm 1 animal, 2 mm 2 animals) were selected, and the size changes thereof were compared on the cone-beam computed tomography (CBCT) D0 (imaging immediately after marker injection) image and D11 (last imaging) image MATLAB (Version R2012a, The Math Works, Inc, USA) was used to reconstitute an image in which the outline of the marker corresponding to the cone-beam computed tomography (CBCT) slice image of the barium sulfate (BaSO.sub.4) marker, and then the image was made to have a 3D volume, of which voxels were then converted into volume values for comparison (table 2 and
(38) TABLE-US-00002 TABLE 2 D11 Size D0 volume volume (D0) Reduction Marker Mouse (mm) (cm.sup.3) (cm.sup.3) (D11) (%) B1 No. 5 1 0.0085 0.0060 0.0025 29.11 No. 3 2 0.0160 0.0055 0.0105 65.23 No. 1 2 0.0235 0.0138 0.0097 41.24 B2 No. 6 1 0.0072 0.0044 0.0028 39.67 No. 8 2 0.0223 0.0201 0.0022 9.88 No. 2 2 0.0208 0.0179 0.0029 13.43
(39) Image Distortion Evaluation Results-Area Histogram Analysis
(40) In order to evaluate the degree of image distortion of the barium sulfate (BaSO.sub.4) marker, the degree of image distortion was compared between the barium sulfate (BaSO.sub.4) marker and the gold marker. B1 marker, B2 marker, and a gold marker commercialized product (Gold marker, diameter: 1 mm, length: 3 mm, CIVCO, USA) were housed inside the polymethacrylicacidmethyl (PMMA) phantom, and the image acquisition condition values (300 mA, 120 kV, slice thickness 1.25 mm, 512512 pixels) were set, and computed tomography (CT) imager (LightSpeed RT 16, GE Healthcare, USA) was used for imaging. The region of interest (ROI) image in the coronal direction, on which B1 marker, B2 marker, and the gold marker were placed, were set to 2020 pixels (15.615.6 mm.sup.2), and then the degree of image distortion was analyzed by the histogram for two-dimensional analysis. For accurate comparison and analysis, the area of each marker was excluded, and for quantitative evaluation, the mean value and standard deviation value of Hounsfield unit (HU) were analyzed.
(41) The Hounsfield Unit (HU) number around the gold marker has a mean value of 93.31 and a variance value of 5.5310.sup.4; the Hounsfield Unit (HU) number around B1 marker had a mean value of 148.95 and a variance value of 3.0110.sup.3; and the Hounsfield Unit (HU) number around B2 marker had a mean value of 155.67 and a variance value of 2.5310.sup.3. With respect to comparison of variance distribution, the gold marker was different from B1 marker and B2 marker by about 20 fold. This shows that the degree of image distortion in the periphery of a marker was more serious in the gold marker than B1 marker and B2 marker.
(42) Such image distortion of the gold marker makes it difficult to differentiate the tumor tissue from the surrounding normal tissues, thereby increasing the inaccuracy in creating the accurate therapy plan. Therefore, the use of the barium sulfate (BaSO.sub.4) marker of the present invention for radiotherapy minimizes the image distortion, thereby differentiating the tumor tissue from the surrounding normal tissues more clearly, and thus can help creating the accurate therapy plan.
(43) Monte Carlo Simulation Dose Distortion Results
(44) The gold marker showed dose distortion of 15.05% in a parallel direction and 9.77% in a perpendicular direction; the stainless steel marker showed dose distortion of 7.92% in a parallel direction and 4.43% in a perpendicular direction; and the titanium marker showed dose distortion of 6.92% in a parallel direction and 0.78% in a perpendicular direction. The barium sulfate (BaSO.sub.4) marker showed a dose distortion result of 3.79% in a parallel direction and 0.53% in a perpendicular direction. Such results were similar to or lower than those of stainless steel and titanium, which showed lower degrees of dose distortion (
(45) Features and advantages of the present invention are summarized as follows.
(46) (i) The present invention relates to a fiducial marker comprising barium sulfate (BaSO.sub.4), a solvent, and a polyethylene glycol-poly(aminoureaurethane) multi-block copolymer, as active ingredients.
(47) (ii) The fiducial marker of the present invention has an effect of significantly solving disadvantages of image distortion and dose distortion, which are involved in the gold inner marker used in the conventional art.
(48) (iii) The fiducial marker of the present invention has very limited in vivo mobility, and thus the fiducial marker is maintained at the position at which it has been initially injected into the body.
(49) (iv) Since the fiducial marker of the present invention is maintained in a sol or liquid phase before in vivo injection, and transited into a gel or solid phase after in vivo injection, the injectability of the fiducial marker by an injector syringe is favorable, and the phase of the fiducial marker can be controlled into a phase suitable to each site of the therapeutic target.
(50) Although the present invention has been described in detail with reference to the specific features, it will be apparent to those skilled in the art that this description is only for a preferred embodiment and does not limit the scope of the present invention. Thus, the substantial scope of the present invention will be defined by the appended claims and equivalents thereof.