- Email: [email protected]
High-resolution gel dosimetry using flat-panel detector cone-beam computed tomography: Preliminary study
ARTICLE IN PRESS Applied Radiation and Isotopes 68 (2010) 607–609
Contents lists available at ScienceDirect
Applied Radiation and Isotopes journal homepage: www.elsevier.com/locate/apradiso
High-resolution gel dosimetry using flat-panel detector cone-beam computed tomography: Preliminary study Kuo-Ming Huang a,b, Tzung-Chi Huang c, Chia-Jung Tsai f, Kun-Mu Lu d, Liang-Kuang Chen b,d,e,, Tung-Hsin Wu f, a
Division of Radiation Oncology, Department of Oncology, and Cancer Research Center, National Taiwan University Hospital, Taiwan Department of Radiological Technology, Yuanpei University, Taiwan c Department of Biomedical Imaging and Radiological Science, China Medical University, Taiwan d Department of Radiology, Shin Kong Wu Ho-Su Memorial Hospital, Taipei, Taiwan e College of Medicine, Fu Jen Catholic University, Taipei, Taiwan f Department of Biomedical Imaging and Radiological Sciences, National Yang Ming University, Taipei, Taiwan b
a r t i c l e in fo
Keywords: MAGAT gel dosimetry Cone-beam CT Multi-detector row CT
abstract This study compares the dose response of irradiated polymer gel with acrylic and styrofoam housing while applying multi-detector CT (MDCT) and cone-beam CT (CBCT). The dose response for MDCT and CBCT, while using an acrylic phantom is 1.34 and 0.67 DHU Gy 1, respectively, and becomes 1.54 and 0.84 DHU Gy 1 while using styrofoam, suggesting styrofoam is the better housing material. While the dose response of MDCT is better than that of CBCT, CBCT is yet a promising 3D dosimetry technique, given its potentially better spatial resolution and sensitive dose interpretation capability. & 2009 Elsevier Ltd. All rights reserved.
1. Introduction Gel dosimetry is the most promising 3D dosimetry technique in current radiation therapy practice. Magnetic resonance imaging (MR) is a popular method for dose information extraction from irradiated gel dosimeter (Maryanski et al., 1993). However, the lack of access to MRI scanners in the clinical radiation therapy setting hinders further development in MRI gel dosimetry techniques. Therefore, X-ray computed tomography (CT), a prevalent imaging modality, has been recently investigated for its feasibility in providing 3D dose information from polymer gel dosimeters. This is possible because a radiation-induced density change can provide contrast in CT images. While previous work by Hilts et al. (2000) has demonstrated the potential of X-ray CT technique for polyacrylamide polymer gels (PAGs), the technique is still in a preliminary stage and has not been thoroughly studied, for example exploring its feasibility when applying to other polymer gels. Specifically, there are several issues in the use of PAG polymer gels including high toxicity and complicated preparation procedures. Therefore, a normoxic polymer gel dosimeter (MAG) is
Corresponding author. Department of Diagnostic Radiology, Shin Kong Wu HoSu Memorial Hospital, 95, Wen Chang Road, Shin Lin, Taipei, Taiwan. Tel.: + 886 2 28332211x2132; fax: +886 2 28389359. Corresponding author. Department of Biomedical Imaging and Radiological Sciences, National Yang Ming University, 155 Li-Nong St., Sec. 2, Taipei 112, Taiwan. Tel.: + 886 2 28267061; fax: +886 2 28201095. E-mail addresses: [email protected] (L.-K. Chen), [email protected] (T.-H. Wu).
0969-8043/$ - see front matter & 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.apradiso.2009.10.036
introduced to overcome aforementioned problems encountered in traditional PAGs polymer gel (Fong et al., 2001). Among which, MAGAT, a more stable and less toxic MAG gel, has been recognized as a promising tool (Bayreder et al., 2006). To date, multi-detector X-ray CT (MDCT) has remained by far the most popular CT method for dose response measurement from irradiated gel dosimeters (Hilts et al., 2005; Hill et al., 2005). However, with the rapid improvements of X-ray CT techniques, some other advanced CT systems such as cone beam X-ray CT (CBCT) may potentially improve the performance of CT gel dosimetry. CBCT typically employs a large-area-detector with 1000 or more detector rows, whereas only 16–64 rows are used in current MDCT. Therefore, with a single rotation around the patient, a complete volume can be reconstructed in CBCT with nearly isotropic, sub-millimeter spatial resolution (Hirota et al., 2006). With the advent of flat-panel-detector-based CBCT, cone beam CT imaging not only can yield much higher spatial resolution images in the 3D reconstructed volume, but also can provide efficient real-time acquisitions without geometric distortions. The volumetric contrast resolution can also be improved by this increased dynamic range. On the other hand, the incorporation of dense gel dosimeter housing could also alter the inherent dose response behavior of the gel we used, since dense material could decrease the number of transmitting photons and increase photon attenuation effect. Therefore, to achieve high dose sensitivity of CT gel dosimetry technique, aforementioned aspects should be taken into consideration. The purpose of this study is to evaluate the dose response of MAGAT gel dosimeters while using CBCT and MDCT. By employing
ARTICLE IN PRESS 608
K.-M. Huang et al. / Applied Radiation and Isotopes 68 (2010) 607–609
the optimal imaging protocol, dose information from MAGAT dosimeter were characterized. In addition, the influence of housing materials, specifically, styrofoam and acrylic, on gel dose sensitivity curve were also investigated.
2. Materials and methods 2.1. Gel preparation and phantom design The MAGAT normoxic polymer gel was prepared under normal oxygen conditions using gelatin (porcine skin, type A, 300 Bloom, Sigma Aldrich), methacrylic acid (monomer purity 498%, Sigma Aldrich), tetrakis hydroxyl methyl phosphonium chloride (THPC) solution (80% solution in water, Sigma Aldrich), as an oxygen scavenger, and distilled water (high performance liquid chromatography grade) (Table 1). The gelatin was given to distilled water and heated to 50 1C in a water bath. A clear solution was achieved and cooled down to 35 1C. The methacrylic acid and THPC solution were then added to the gelatin solution. A homogeneous liquid mixture was achieved by continuous stirring. All MAGAT gels were poured into 22 60 ml of plastic vials with 25 mm in diameter and 115 mm in height. MAGAT gel vials were irradiated by a 6 MV Varian linear accelerator with doses of 0, 1.8, 4, 6, 8, 10, 12, 14, 16, 18 and 20 Gy. Each vial was wrapped in 2 cm of bolus material to provide a sufficient buildup region of dose in the vial. Wrapped vial was placed in a styrofoam cradle during irradiation in order to prevent back scattering. Two parallel opposite beams were given to each vial with gantry rotation at 901 and 2701. After irradiation, all vials were inserted into containers of two different housing materials, acrylic (Fig. 1a) and styrofoam cradle (Fig. 1b). 2.2. Image acquisition and data analysis MDCT imaging of the irradiated MAGAT dosimeters were performed using a Siemens SOMATOM Sensation CT scanner Table 1 Composition of 100 ml MAGAT gel. Chemical
Concentration
Gelatine Methacrylic acid (MAA) THPC Distilled water
6%, 6 g 9%, 9 g 10 mM 85%, 85 ml
(Siemens Medical System, Berlin, and Germany), which is a 16slice scanner, 3rd generation, rotate–rotate machine. Irradiated MAGAT dosimeters and unirradiated MAGAT dosimeters used for background subtraction, were positioned and oriented identically within the scanner bore using acrylic phantom (Fig. 1a) and styrofoam cradle (Fig. 1b). MDCT images were acquired at 120 kVp of tube voltage, 250 mA of tube current, and 0.5 s of X-ray tube rotation time. Pitch was set to 1 in this study. While signal-tonoise ratio (SNR) in the CT images is relatively low, it can be improved by averaging CT images of an irradiated polymer gel dosimeter. Therefore, for this particular reason, 10 slices of images were acquired for image averaging with the slice thickness of 1 cm. Irradiated MAGAT dosimeters were also scanned with a Philips Allura Xper FD20 C-arm cone beam CT (Philips Medical System, Netherlands), with the same positioning as MDCT scan. The CBCT scan was performed with parameters of 119 kVp, 142 mA and 4.1 s of gantry rotation time. The 10 slices of transverse reconstruction images of the acquired cone-beam projection data with slice thickness of 3 mm were acquired for averaging. In this study, both MDCT and CBCT images were transferred to DICOM format and all the data processing and analysis was done using Matlab (Mathworks, Inc.). Image was performed by averaging multiple slices of the vials at the same region of interest (ROI) section with unit of the CT number difference, socalled DHU, after background subtraction.
3. Results and discussion Fig. 2 shows the results of dose response while using acrylic and styrofoam as a phantom housing material for the gel vials during imaging, respectively. In Fig. 2a, the measured slope of dose response for MDCT and CBCT while using acrylic housing was 1.34 and 0.68 DHU Gy 1, respectively. Linear correlation coefficient for MDCT is 0.98, and it is 0.97 for CBCT. While using styrofoam housing, the measured slope of dose response for MDCT and CBCT became 1.54 and 0.84 DHU Gy 1, respectively (Fig 2b). Here, linear correlation coefficient for MDCT is 0.99, and it is 0.87 for CBCT. Both studies show that overall dose sensitivity of MDCT is better than that of CBCT by a factor of 2. Comparing Fig 2a and b, it is obvious that using styrofoam as a housing material was better than using the acrylic phantom in terms of improved dose response performance. The implication is that, the use of high-density acrylic phantom could cause more attenuation of lower energy X-ray photons at the surrounding
Fig. 1. Two materials for gel housing phantom: (a) acrylic and (b) styrofoam. Vials were inserted in the phantoms for positioning during CT imaging.
ARTICLE IN PRESS K.-M. Huang et al. / Applied Radiation and Isotopes 68 (2010) 607–609
40
40 MDCT: ΔHU = 1.34 ⋅ Dose – 0.036 R-square = 0.98
35 30
30
25
25
20
20
15
15
10
10
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CBCT: ΔHU = 0.68 ⋅ Dose –0.11 R-square = 0.97
0 0
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6
8 10 12 14 16 18 20 22
MDCT: ΔHU = 1.54 ⋅ Dose + 5.18 R-square = 0.99
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ΔHU
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CBCT: ΔHU = 0.84 ⋅ Dose + 6.29 R-square = 0.87
5 0 0
2
Dose (cGy)
4
6
8 10 12 14 16 18 20 22 Dose (cGy)
Fig. 2. Absorbed dose versus signal intensity when using: (a) acrylic and (b) styrofoam housing phantom for the vials during imaging. Solid and dashed line represent results from MDCT and CBCT, respectively.
shell of the phantom and result in a, so-called, beam hardening effect. This effect makes it difficult to remove noise with background subtraction and also may increase obscurity in dose information extraction. Despite its lower dose response, the standard deviation of the measured signal intensity from CBCT is overall smaller than that from MDCT. This could be attributed to the noise reduction effect of the temporal artifact correction technique in CBCT image preprocessing step. In this study, the results from CBCT were poorer quality than those from MDCT. It was because the exposure factors of CBCT were automatically selected by the machine. Since manual adjustment of scanning parameters is not allowed, an optimal protocol for CBCT cannot be achieved in current practice. Therefore, the results of this study do not necessarily represent the overall system performance in CBCT. On the other hand, with a dynamic range of up to 14 bits compared to 12 bits in MDCT, rapid image acquisition, and superior noise reduction observed in this study, CBCT still appears to offer potential as a promising imaging tool for CT gel dosimetry techniques.
4. Conclusion In this work, we have investigated the influence of phantom design, and different CT techniques on the performance of MAGAT gel dosimetry method. This study is the first attempt to explore the potential role of CBCT in gel dosimetry techniques. While the firm conclusions cannot be drawn from our preliminary study, the wide dynamic range and high image contrast of CBCT still justifies
the further research efforts to better understand the potential of CBCT-based gel dosimetry techniques in clinical applications.
Acknowledgments This study was financially supported in part by the National Science Council of Taiwan (NSC96-2321-B-010-009-MY3) and by the grant of Shin Kong Wu Ho-Su Memorial Hospital (SKH-830294-DR-36). References Bayreder, C., Georg, D., Moser, E., Berg, A., 2006. Basic investigations on the performance of a normoxic polymer gel with tetrakis-hydroxy-methylphosphonium chloride as an oxygen scavenger: reproducibliity, accuracy, stability, and dose rate dependence. Med. Phys. 33 (7), 2506–2518. Fong, P.M., Keil, D.C., Does, M.D., Gore, J.C., 2001. Polymer gels for magnetic resonance imaging of radiation dose distributions at normal room atmosphere. Phys. Med. Biol. 46 (12), 3105–3113. Hill, B., Venning, A., Baldock, C., 2005. The dose response of normoxic polymer gel dosimeters measured using X-ray CT. Br. J. Radiol. 78, 623–630. Hilts, M., Audet, C., Duzenli, C., Jirasek, A., 2000. Polymer gel dosimetry using X-ray computed tomography: a feasibility study. Phys. Med. Biol. 45 (9), 2559–2571. Hilts, M., Jirasek, A., Duzznli, C., 2005. Technical considerations for implementation of X-ray CT polymer gel dosimetry. Phys. Med. Biol. 50 (8), 1727–1745. Hirota, S., Nakao, N., Yamamoto, S., Kobayashi, K., Maeda, H., Ishikura, R., Miura, K., Sakamoto, K., Ueda, K., Baba, R., 2006. Cone-beam CT with flat-panel-detector digital angiography system: early experience in abdominal interventional procedures. Cardiovasc. Intervent Radiol. 29 (6), 1034–1038. Maryanski, M.J., Gore, J.C., Kennan, R.P., Schulz, R.J., 1993. NMR relaxation enhancement in gels polymerized and cross-linked by ionizing radiation: a new approach to 3D dosimetry by MRI. Magn. Reson. Imaging 11 (2), 253–258.
Contents lists available at ScienceDirect
Applied Radiation and Isotopes journal homepage: www.elsevier.com/locate/apradiso
High-resolution gel dosimetry using flat-panel detector cone-beam computed tomography: Preliminary study Kuo-Ming Huang a,b, Tzung-Chi Huang c, Chia-Jung Tsai f, Kun-Mu Lu d, Liang-Kuang Chen b,d,e,, Tung-Hsin Wu f, a
Division of Radiation Oncology, Department of Oncology, and Cancer Research Center, National Taiwan University Hospital, Taiwan Department of Radiological Technology, Yuanpei University, Taiwan c Department of Biomedical Imaging and Radiological Science, China Medical University, Taiwan d Department of Radiology, Shin Kong Wu Ho-Su Memorial Hospital, Taipei, Taiwan e College of Medicine, Fu Jen Catholic University, Taipei, Taiwan f Department of Biomedical Imaging and Radiological Sciences, National Yang Ming University, Taipei, Taiwan b
a r t i c l e in fo
Keywords: MAGAT gel dosimetry Cone-beam CT Multi-detector row CT
abstract This study compares the dose response of irradiated polymer gel with acrylic and styrofoam housing while applying multi-detector CT (MDCT) and cone-beam CT (CBCT). The dose response for MDCT and CBCT, while using an acrylic phantom is 1.34 and 0.67 DHU Gy 1, respectively, and becomes 1.54 and 0.84 DHU Gy 1 while using styrofoam, suggesting styrofoam is the better housing material. While the dose response of MDCT is better than that of CBCT, CBCT is yet a promising 3D dosimetry technique, given its potentially better spatial resolution and sensitive dose interpretation capability. & 2009 Elsevier Ltd. All rights reserved.
1. Introduction Gel dosimetry is the most promising 3D dosimetry technique in current radiation therapy practice. Magnetic resonance imaging (MR) is a popular method for dose information extraction from irradiated gel dosimeter (Maryanski et al., 1993). However, the lack of access to MRI scanners in the clinical radiation therapy setting hinders further development in MRI gel dosimetry techniques. Therefore, X-ray computed tomography (CT), a prevalent imaging modality, has been recently investigated for its feasibility in providing 3D dose information from polymer gel dosimeters. This is possible because a radiation-induced density change can provide contrast in CT images. While previous work by Hilts et al. (2000) has demonstrated the potential of X-ray CT technique for polyacrylamide polymer gels (PAGs), the technique is still in a preliminary stage and has not been thoroughly studied, for example exploring its feasibility when applying to other polymer gels. Specifically, there are several issues in the use of PAG polymer gels including high toxicity and complicated preparation procedures. Therefore, a normoxic polymer gel dosimeter (MAG) is
Corresponding author. Department of Diagnostic Radiology, Shin Kong Wu HoSu Memorial Hospital, 95, Wen Chang Road, Shin Lin, Taipei, Taiwan. Tel.: + 886 2 28332211x2132; fax: +886 2 28389359. Corresponding author. Department of Biomedical Imaging and Radiological Sciences, National Yang Ming University, 155 Li-Nong St., Sec. 2, Taipei 112, Taiwan. Tel.: + 886 2 28267061; fax: +886 2 28201095. E-mail addresses: [email protected] (L.-K. Chen), [email protected] (T.-H. Wu).
0969-8043/$ - see front matter & 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.apradiso.2009.10.036
introduced to overcome aforementioned problems encountered in traditional PAGs polymer gel (Fong et al., 2001). Among which, MAGAT, a more stable and less toxic MAG gel, has been recognized as a promising tool (Bayreder et al., 2006). To date, multi-detector X-ray CT (MDCT) has remained by far the most popular CT method for dose response measurement from irradiated gel dosimeters (Hilts et al., 2005; Hill et al., 2005). However, with the rapid improvements of X-ray CT techniques, some other advanced CT systems such as cone beam X-ray CT (CBCT) may potentially improve the performance of CT gel dosimetry. CBCT typically employs a large-area-detector with 1000 or more detector rows, whereas only 16–64 rows are used in current MDCT. Therefore, with a single rotation around the patient, a complete volume can be reconstructed in CBCT with nearly isotropic, sub-millimeter spatial resolution (Hirota et al., 2006). With the advent of flat-panel-detector-based CBCT, cone beam CT imaging not only can yield much higher spatial resolution images in the 3D reconstructed volume, but also can provide efficient real-time acquisitions without geometric distortions. The volumetric contrast resolution can also be improved by this increased dynamic range. On the other hand, the incorporation of dense gel dosimeter housing could also alter the inherent dose response behavior of the gel we used, since dense material could decrease the number of transmitting photons and increase photon attenuation effect. Therefore, to achieve high dose sensitivity of CT gel dosimetry technique, aforementioned aspects should be taken into consideration. The purpose of this study is to evaluate the dose response of MAGAT gel dosimeters while using CBCT and MDCT. By employing
ARTICLE IN PRESS 608
K.-M. Huang et al. / Applied Radiation and Isotopes 68 (2010) 607–609
the optimal imaging protocol, dose information from MAGAT dosimeter were characterized. In addition, the influence of housing materials, specifically, styrofoam and acrylic, on gel dose sensitivity curve were also investigated.
2. Materials and methods 2.1. Gel preparation and phantom design The MAGAT normoxic polymer gel was prepared under normal oxygen conditions using gelatin (porcine skin, type A, 300 Bloom, Sigma Aldrich), methacrylic acid (monomer purity 498%, Sigma Aldrich), tetrakis hydroxyl methyl phosphonium chloride (THPC) solution (80% solution in water, Sigma Aldrich), as an oxygen scavenger, and distilled water (high performance liquid chromatography grade) (Table 1). The gelatin was given to distilled water and heated to 50 1C in a water bath. A clear solution was achieved and cooled down to 35 1C. The methacrylic acid and THPC solution were then added to the gelatin solution. A homogeneous liquid mixture was achieved by continuous stirring. All MAGAT gels were poured into 22 60 ml of plastic vials with 25 mm in diameter and 115 mm in height. MAGAT gel vials were irradiated by a 6 MV Varian linear accelerator with doses of 0, 1.8, 4, 6, 8, 10, 12, 14, 16, 18 and 20 Gy. Each vial was wrapped in 2 cm of bolus material to provide a sufficient buildup region of dose in the vial. Wrapped vial was placed in a styrofoam cradle during irradiation in order to prevent back scattering. Two parallel opposite beams were given to each vial with gantry rotation at 901 and 2701. After irradiation, all vials were inserted into containers of two different housing materials, acrylic (Fig. 1a) and styrofoam cradle (Fig. 1b). 2.2. Image acquisition and data analysis MDCT imaging of the irradiated MAGAT dosimeters were performed using a Siemens SOMATOM Sensation CT scanner Table 1 Composition of 100 ml MAGAT gel. Chemical
Concentration
Gelatine Methacrylic acid (MAA) THPC Distilled water
6%, 6 g 9%, 9 g 10 mM 85%, 85 ml
(Siemens Medical System, Berlin, and Germany), which is a 16slice scanner, 3rd generation, rotate–rotate machine. Irradiated MAGAT dosimeters and unirradiated MAGAT dosimeters used for background subtraction, were positioned and oriented identically within the scanner bore using acrylic phantom (Fig. 1a) and styrofoam cradle (Fig. 1b). MDCT images were acquired at 120 kVp of tube voltage, 250 mA of tube current, and 0.5 s of X-ray tube rotation time. Pitch was set to 1 in this study. While signal-tonoise ratio (SNR) in the CT images is relatively low, it can be improved by averaging CT images of an irradiated polymer gel dosimeter. Therefore, for this particular reason, 10 slices of images were acquired for image averaging with the slice thickness of 1 cm. Irradiated MAGAT dosimeters were also scanned with a Philips Allura Xper FD20 C-arm cone beam CT (Philips Medical System, Netherlands), with the same positioning as MDCT scan. The CBCT scan was performed with parameters of 119 kVp, 142 mA and 4.1 s of gantry rotation time. The 10 slices of transverse reconstruction images of the acquired cone-beam projection data with slice thickness of 3 mm were acquired for averaging. In this study, both MDCT and CBCT images were transferred to DICOM format and all the data processing and analysis was done using Matlab (Mathworks, Inc.). Image was performed by averaging multiple slices of the vials at the same region of interest (ROI) section with unit of the CT number difference, socalled DHU, after background subtraction.
3. Results and discussion Fig. 2 shows the results of dose response while using acrylic and styrofoam as a phantom housing material for the gel vials during imaging, respectively. In Fig. 2a, the measured slope of dose response for MDCT and CBCT while using acrylic housing was 1.34 and 0.68 DHU Gy 1, respectively. Linear correlation coefficient for MDCT is 0.98, and it is 0.97 for CBCT. While using styrofoam housing, the measured slope of dose response for MDCT and CBCT became 1.54 and 0.84 DHU Gy 1, respectively (Fig 2b). Here, linear correlation coefficient for MDCT is 0.99, and it is 0.87 for CBCT. Both studies show that overall dose sensitivity of MDCT is better than that of CBCT by a factor of 2. Comparing Fig 2a and b, it is obvious that using styrofoam as a housing material was better than using the acrylic phantom in terms of improved dose response performance. The implication is that, the use of high-density acrylic phantom could cause more attenuation of lower energy X-ray photons at the surrounding
Fig. 1. Two materials for gel housing phantom: (a) acrylic and (b) styrofoam. Vials were inserted in the phantoms for positioning during CT imaging.
ARTICLE IN PRESS K.-M. Huang et al. / Applied Radiation and Isotopes 68 (2010) 607–609
40
40 MDCT: ΔHU = 1.34 ⋅ Dose – 0.036 R-square = 0.98
35 30
30
25
25
20
20
15
15
10
10
5
CBCT: ΔHU = 0.68 ⋅ Dose –0.11 R-square = 0.97
0 0
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8 10 12 14 16 18 20 22
MDCT: ΔHU = 1.54 ⋅ Dose + 5.18 R-square = 0.99
35
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ΔHU
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CBCT: ΔHU = 0.84 ⋅ Dose + 6.29 R-square = 0.87
5 0 0
2
Dose (cGy)
4
6
8 10 12 14 16 18 20 22 Dose (cGy)
Fig. 2. Absorbed dose versus signal intensity when using: (a) acrylic and (b) styrofoam housing phantom for the vials during imaging. Solid and dashed line represent results from MDCT and CBCT, respectively.
shell of the phantom and result in a, so-called, beam hardening effect. This effect makes it difficult to remove noise with background subtraction and also may increase obscurity in dose information extraction. Despite its lower dose response, the standard deviation of the measured signal intensity from CBCT is overall smaller than that from MDCT. This could be attributed to the noise reduction effect of the temporal artifact correction technique in CBCT image preprocessing step. In this study, the results from CBCT were poorer quality than those from MDCT. It was because the exposure factors of CBCT were automatically selected by the machine. Since manual adjustment of scanning parameters is not allowed, an optimal protocol for CBCT cannot be achieved in current practice. Therefore, the results of this study do not necessarily represent the overall system performance in CBCT. On the other hand, with a dynamic range of up to 14 bits compared to 12 bits in MDCT, rapid image acquisition, and superior noise reduction observed in this study, CBCT still appears to offer potential as a promising imaging tool for CT gel dosimetry techniques.
4. Conclusion In this work, we have investigated the influence of phantom design, and different CT techniques on the performance of MAGAT gel dosimetry method. This study is the first attempt to explore the potential role of CBCT in gel dosimetry techniques. While the firm conclusions cannot be drawn from our preliminary study, the wide dynamic range and high image contrast of CBCT still justifies
the further research efforts to better understand the potential of CBCT-based gel dosimetry techniques in clinical applications.
Acknowledgments This study was financially supported in part by the National Science Council of Taiwan (NSC96-2321-B-010-009-MY3) and by the grant of Shin Kong Wu Ho-Su Memorial Hospital (SKH-830294-DR-36). References Bayreder, C., Georg, D., Moser, E., Berg, A., 2006. Basic investigations on the performance of a normoxic polymer gel with tetrakis-hydroxy-methylphosphonium chloride as an oxygen scavenger: reproducibliity, accuracy, stability, and dose rate dependence. Med. Phys. 33 (7), 2506–2518. Fong, P.M., Keil, D.C., Does, M.D., Gore, J.C., 2001. Polymer gels for magnetic resonance imaging of radiation dose distributions at normal room atmosphere. Phys. Med. Biol. 46 (12), 3105–3113. Hill, B., Venning, A., Baldock, C., 2005. The dose response of normoxic polymer gel dosimeters measured using X-ray CT. Br. J. Radiol. 78, 623–630. Hilts, M., Audet, C., Duzenli, C., Jirasek, A., 2000. Polymer gel dosimetry using X-ray computed tomography: a feasibility study. Phys. Med. Biol. 45 (9), 2559–2571. Hilts, M., Jirasek, A., Duzznli, C., 2005. Technical considerations for implementation of X-ray CT polymer gel dosimetry. Phys. Med. Biol. 50 (8), 1727–1745. Hirota, S., Nakao, N., Yamamoto, S., Kobayashi, K., Maeda, H., Ishikura, R., Miura, K., Sakamoto, K., Ueda, K., Baba, R., 2006. Cone-beam CT with flat-panel-detector digital angiography system: early experience in abdominal interventional procedures. Cardiovasc. Intervent Radiol. 29 (6), 1034–1038. Maryanski, M.J., Gore, J.C., Kennan, R.P., Schulz, R.J., 1993. NMR relaxation enhancement in gels polymerized and cross-linked by ionizing radiation: a new approach to 3D dosimetry by MRI. Magn. Reson. Imaging 11 (2), 253–258.