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Volumn 40, Issue 1, 2013, Pages

A comparative study of small field total scatter factors and dose profiles using plastic scintillation detectors and other stereotactic dosimeters: The case of the CyberKnife

Author keywords

CyberKnife system; dose profiles; plastic scintillation detectors; stereotactic radiosurgery; total scatter factors

Indexed keywords

DIODES; DOSIMETERS; DOSIMETRY; MONTE CARLO METHODS; QUALITY ASSURANCE; RADIOTHERAPY; SCINTILLATION; WATER TANKS;

EID: 84872017389     PISSN: 00942405     EISSN: None     Source Type: Journal    
DOI: 10.1118/1.4772190     Document Type: Article
Times cited : (83)

References (43)
  • 2
    • 0037234447 scopus 로고    scopus 로고
    • An analysis of the accuracy of the cyberknife: A robotic frameless stereotactic radiosurgical system
    • DOI 10.1097/00006123-200301000-00018
    • S. D. Chang, W. Main, D. P. Martin, I. C. Gibbs, and M. P. Heibrun, " An analysis of the accuracy of the CyberKnife: A robotic frameless stereotactic radiosurgical system.," Neurosurgery 52, 140-147 (2003). 10.1097/00006123-200301000-00018 (Pubitemid 36098663)
    • (2003) Neurosurgery , vol.52 , Issue.1 , pp. 140-147
    • Chang, S.D.1    Main, W.2    Martin, D.P.3    Gibbs, I.C.4    Heilbrun, M.P.5    Kelly, P.J.6    Loeffler, J.S.7    Bussiere, M.R.8    Yu, C.9
  • 3
    • 51849098609 scopus 로고    scopus 로고
    • Performance evaluation of a Cyberknife® G4 image-guided robotic stereotactic radiosurgery system
    • 10.1088/0031-9155/53/17/016
    • C. Antypas and E. Pantelis, " Performance evaluation of a Cyberknife® G4 image-guided robotic stereotactic radiosurgery system.," Phys. Med. Biol. 53, 4697-4718 (2008). 10.1088/0031-9155/53/17/016
    • (2008) Phys. Med. Biol. , vol.53 , pp. 4697-4718
    • Antypas, C.1    Pantelis, E.2
  • 4
    • 0031687825 scopus 로고    scopus 로고
    • Small photon field dosimetry for stereotactic radiosurgery
    • DOI 10.1016/S0958-3947(98)00013-2, PII S0958394798000132
    • D. M. Duggan and C. W. Coffey II, " Small photon field dosimetry for stereotactic radiosurgery.," Med. Dosim. 23, 153-159 (1998). 10.1016/S0958-3947(98)00013-2 (Pubitemid 28463072)
    • (1998) Medical Dosimetry , vol.23 , Issue.3 , pp. 153-159
    • Duggan, D.M.1    Coffey, C.W.2
  • 5
    • 38849151519 scopus 로고    scopus 로고
    • Total scatter factors of small beams: A multidetector and Monte Carlo study
    • DOI 10.1118/1.2828195
    • P. Francescon, S. Cora, and C. Cavedon, " Total scatter factors of small beams: A multidetector and Monte Carlo study.," Med. Phys. 35, 504-513 (2008). 10.1118/1.2828195 (Pubitemid 351190870)
    • (2008) Medical Physics , vol.35 , Issue.2 , pp. 504-513
    • Francescon, P.1    Cora, S.2    Cavedon, C.3
  • 7
    • 0037339773 scopus 로고    scopus 로고
    • The volume effect of detectors in the dosimetry of small fields used in IMRT
    • DOI 10.1118/1.1544678
    • W. U. Laub and T. Wong, " The volume effect of detectors in the dosimetry of small fields used in IMRT.," Med. Phys. 30, 341-347 (2003). 10.1118/1.1544678 (Pubitemid 36337100)
    • (2003) Medical Physics , vol.30 , Issue.3 , pp. 341-347
    • Lauba, W.U.1    Wong, T.2
  • 8
    • 33746605979 scopus 로고    scopus 로고
    • Monte Carlo study of a Cyberknife stereotactic radiosurgery system
    • DOI 10.1118/1.2219774
    • F. Araki, " Monte Carlo study of a Cyberknife stereotactic radiosurgery system.," Med. Phys. 33, 2955-2963 (2006). 10.1118/1.2219774 (Pubitemid 44154569)
    • (2006) Medical Physics , vol.33 , Issue.8 , pp. 2955-2963
    • Araki, F.1
  • 9
    • 0030026160 scopus 로고    scopus 로고
    • A comparison of dosimetry techniques in stereotactic radiosurgery
    • DOI 10.1088/0031-9155/41/1/008
    • M. Heydarian, P. W. Hoban, and A. H. Beddoe, " A comparison of dosimetry techniques in stereotactic radiosurgery.," Phys. Med. Biol. 41, 93-110 (1996). 10.1088/0031-9155/41/1/008 (Pubitemid 26034227)
    • (1996) Physics in Medicine and Biology , vol.41 , Issue.1 , pp. 93-110
    • Heydarian, M.1    Hoban, P.W.2    Beddoe, A.H.3
  • 10
    • 0037035943 scopus 로고    scopus 로고
    • Investigation of photon beam output factors for conformal radiation therapy - Monte Carlo simulations and measurements
    • DOI 10.1088/0031-9155/47/11/401, PII S0031915502323959
    • F. Haryanto, M. Fippel, W. Laub, O. Dohm, and F. Nüsslin, " Investigation of photon beam output factors for conformal radiation therapy-Monte Carlo simulations and measurements.," Phys. Med. Biol. 47, N133-N143 (2002). 10.1088/0031-9155/47/11/401 (Pubitemid 34662209)
    • (2002) Physics in Medicine and Biology , vol.47 , Issue.11
    • Haryanto, F.1    Fippel, M.2    Laub, W.3    Dohm, O.4    Nusslin, F.5
  • 12
    • 34447336432 scopus 로고    scopus 로고
    • Measurement of output factors for small photon beams
    • DOI 10.1118/1.2734383
    • O. A. Sauer and J. Wilbert, " Measurement of output factors for small photon beams.," Med. Phys. 34, 1983-1988 (2007). 10.1118/1.2734383 (Pubitemid 47055733)
    • (2007) Medical Physics , vol.34 , Issue.6 , pp. 1983-1988
    • Sauer, O.A.1    Wilbert, J.2
  • 13
    • 33947400267 scopus 로고    scopus 로고
    • Review of recent advances in non gel dosimeters
    • 10.1088/1742-6596/56/1/011
    • K. Jordan, " Review of recent advances in non gel dosimeters.," J. Phys.: Conf. Ser. 56, 132-141 (2006). 10.1088/1742-6596/56/1/011
    • (2006) J. Phys.: Conf. Ser. , vol.56 , pp. 132-141
    • Jordan, K.1
  • 14
    • 0035355339 scopus 로고    scopus 로고
    • A miniature "scintillator-fiberoptic-PMT" detector system for the dosimetry of small fields in stereotactic radiosurgery
    • DOI 10.1109/23.940133, PII S0018949901047803
    • A. S. Beddar, T. J. Kinsella, A. Ikhlef, and C. H. Sibata, " A miniature "Scintillator-Fiberoptic-PMT" detector system for the dosimetry of small fields in stereotactic radiosurgery.," IEEE Trans. Nucl. Sci. 48, 924-928 (2001). 10.1109/23.940133 (Pubitemid 32968781)
    • (2001) IEEE Transactions on Nuclear Science , vol.48 , Issue.3 , pp. 924-928
    • Beddar, A.S.1    Kinsella, T.J.2    Ikhlef, A.3    Sibata, C.H.4
  • 15
    • 82755198685 scopus 로고    scopus 로고
    • A new water-equivalent 2D plastic scintillation detectors array for the dosimetry of megavoltage energy photon beams in radiation therapy
    • 10.1118/1.3664007
    • M. Guillot, L. Beaulieu, L. Archambault, S. Beddar, and L. Gingras, " A new water-equivalent 2D plastic scintillation detectors array for the dosimetry of megavoltage energy photon beams in radiation therapy.," Med. Phys. 38, 6763-6774 (2011). 10.1118/1.3664007
    • (2011) Med. Phys. , vol.38 , pp. 6763-6774
    • Guillot, M.1    Beaulieu, L.2    Archambault, L.3    Beddar, S.4    Gingras, L.5
  • 16
    • 84855458206 scopus 로고    scopus 로고
    • Dosimetric performance and array assessment of plastic scintillation detectors for stereotactic radiosurgery quality assurance
    • 10.1118/1.3666765
    • J.-C. Gagnon, D. Theriault, M. Guillot, L. Archambault, S. Beddar, L. Gingras, and L. Beaulieu, " Dosimetric performance and array assessment of plastic scintillation detectors for stereotactic radiosurgery quality assurance.," Med. Phys. 39, 429-436 (2012). 10.1118/1.3666765
    • (2012) Med. Phys. , vol.39 , pp. 429-436
    • Gagnon, J.-C.1    Theriault, D.2    Guillot, M.3    Archambault, L.4    Beddar, S.5    Gingras, L.6    Beaulieu, L.7
  • 17
    • 0342614959 scopus 로고    scopus 로고
    • Miniature scintillating detector for small field radiation therapy
    • DOI 10.1118/1.598793
    • D. Letourneau, J. Pouliot, and R. Roy, " Miniature scintillating detector for small field radiation therapy.," Med. Phys. 26, 2555-2561 (1999). 10.1118/1.598793 (Pubitemid 30007699)
    • (1999) Medical Physics , vol.26 , Issue.12 , pp. 2555-2561
    • Letourneau, D.1    Pouliot, J.2    Roy, R.3
  • 18
    • 77957705127 scopus 로고    scopus 로고
    • Measuring output factors of small fields formed by collimator jaws and multileaf collimator using plastic scintillation detectors
    • 10.1118/1.3488981
    • D. M. Klein, R. C. Tailor, L. Archambault, L. Wang, F. Therriault-Proulx, and A. S. Beddar, " Measuring output factors of small fields formed by collimator jaws and multileaf collimator using plastic scintillation detectors.," Med. Phys. 37, 5541-5549 (2010). 10.1118/1.3488981
    • (2010) Med. Phys. , vol.37 , pp. 5541-5549
    • Klein, D.M.1    Tailor, R.C.2    Archambault, L.3    Wang, L.4    Therriault-Proulx, F.5    Beddar, A.S.6
  • 19
    • 79955389725 scopus 로고    scopus 로고
    • Characterizing a pulse-resolved dosimetry system for complex radiotherapy beams using organic scintillators
    • 10.1088/0031-9155/56/10/009
    • A. R. Beierholm, R. O. Ottosson, L. R. Lindvold, C. F. Behrens, and C. E. Andersen, " Characterizing a pulse-resolved dosimetry system for complex radiotherapy beams using organic scintillators.," Phys. Med. Biol. 56, 3033-3045 (2011). 10.1088/0031-9155/56/10/009
    • (2011) Phys. Med. Biol. , vol.56 , pp. 3033-3045
    • Beierholm, A.R.1    Ottosson, R.O.2    Lindvold, L.R.3    Behrens, C.F.4    Andersen, C.E.5
  • 20
    • 84872039399 scopus 로고    scopus 로고
    • Su-e-t-163: Characterization of the response of active detectors and passive dosemeters used for dose measurement in small photon beams
    • 10.1118/1.3612113
    • S. Derreumaux, C. Bassinet, C. Huet, M. Chea, G. Boisserie, G. Brunet, M. Baumann, F. Trompier, P. Roch, and I. Clairand, " Su-e-t-163: Characterization of the response of active detectors and passive dosemeters used for dose measurement in small photon beams.," Med. Phys. 38, 3523-3523 (2011). 10.1118/1.3612113
    • (2011) Med. Phys. , vol.38 , pp. 3523-3523
    • Derreumaux, S.1    Bassinet, C.2    Huet, C.3    Chea, M.4    Boisserie, G.5    Brunet, G.6    Baumann, M.7    Trompier, F.8    Roch, P.9    Clairand, I.10
  • 21
    • 33645009141 scopus 로고    scopus 로고
    • Dosimetric characteristics of a new unshielded silicon diode and its application in clinical photon and electron beams
    • 10.1118/1.2124547
    • I. Griessbach, M. Lapp, J. Bohsung, G. Gademann, and D. Harder, " Dosimetric characteristics of a new unshielded silicon diode and its application in clinical photon and electron beams.," Med. Phys. 32, 3750-3754 (2005). 10.1118/1.2124547
    • (2005) Med. Phys. , vol.32 , pp. 3750-3754
    • Griessbach, I.1    Lapp, M.2    Bohsung, J.3    Gademann, G.4    Harder, D.5
  • 22
    • 77952395736 scopus 로고    scopus 로고
    • Energy dependence and dose response of Gafchromic EBT2 film over a wide range of photon, electron, and proton beam energies
    • 10.1118/1.3373523
    • B. Arjomandy, R. Tailor, A. Anand, N. Sahoo, M. Gillin, K. Prado, and M. Vicic, " Energy dependence and dose response of Gafchromic EBT2 film over a wide range of photon, electron, and proton beam energies.," Med. Phys. 37, 1942-1947 (2010). 10.1118/1.3373523
    • (2010) Med. Phys. , vol.37 , pp. 1942-1947
    • Arjomandy, B.1    Tailor, R.2    Anand, A.3    Sahoo, N.4    Gillin, M.5    Prado, K.6    Vicic, M.7
  • 23
    • 82755194882 scopus 로고    scopus 로고
    • SU-GG-T-329: Gafgui: An open-source project for radiochromic film dosimetry
    • 10.1118/1.3468725
    • H. Bouchard and F. Lacroix, " SU-GG-T-329: Gafgui: An open-source project for radiochromic film dosimetry.," Med. Phys. 37, 3261-3262 (2010). 10.1118/1.3468725
    • (2010) Med. Phys. , vol.37 , pp. 3261-3262
    • Bouchard, H.1    Lacroix, F.2
  • 24
    • 66449085569 scopus 로고    scopus 로고
    • On the characterization and uncertainty analysis of radiochromic film dosimetry
    • 10.1118/1.3121488
    • H. Bouchard, F. Lacroix, G. Beaudoin, J.-F. Carrier, and I. Kawrakow, " On the characterization and uncertainty analysis of radiochromic film dosimetry.," Med. Phys. 36, 1931-1946 (2009). 10.1118/1.3121488
    • (2009) Med. Phys. , vol.36 , pp. 1931-1946
    • Bouchard, H.1    Lacroix, F.2    Beaudoin, G.3    Carrier, J.-F.4    Kawrakow, I.5
  • 25
    • 78149492363 scopus 로고    scopus 로고
    • Extraction of depth-dependent perturbation factors for parallel-plate chambers in electron beams using a plastic scintillation detector
    • 10.1118/1.3463383
    • F. Lacroix, M. Guillot, M. McEwen, C. Cojocaru, L. Gingras, A. S. Beddar, and L. Beaulieu, " Extraction of depth-dependent perturbation factors for parallel-plate chambers in electron beams using a plastic scintillation detector.," Med. Phys. 37, 4331-4342 (2010). 10.1118/1.3463383
    • (2010) Med. Phys. , vol.37 , pp. 4331-4342
    • Lacroix, F.1    Guillot, M.2    McEwen, M.3    Cojocaru, C.4    Gingras, L.5    Beddar, A.S.6    Beaulieu, L.7
  • 26
    • 85027223894 scopus 로고    scopus 로고
    • Ion recombination in a liquid-filled ionization chamber in high-energy photon beams
    • presented at the, Charlotte, NC, July 29 - August 2).
    • E. Chung, S. Davis, and J. Seuntjens, " Ion recombination in a liquid-filled ionization chamber in high-energy photon beams.," presented at the 54th Annual Meeting of the AAPM, Charlotte, NC, July 29-August 2, 2012).
    • (2012) 54th Annual Meeting of the AAPM
    • Chung, E.1    Davis, S.2    Seuntjens, J.3
  • 27
    • 0028133287 scopus 로고
    • Absorbed dose perturbation caused by diodes for small field photon dosimetry
    • DOI 10.1118/1.597350
    • A. S. Beddar, D. J. Mason, and P. F. O'Brien, " Absorbed dose perturbation caused by diodes for small field photon dosimetry.," Med. Phys. 21, 1075-1079 (1994). 10.1118/1.597350 (Pubitemid 24233834)
    • (1994) Medical Physics , vol.21 , Issue.7 , pp. 1075-1079
    • Beddar, A.S.1    Mason, D.J.2    O'Brien, P.F.3
  • 28
    • 0026555508 scopus 로고
    • Cerenkov light generated in optical fibres and other light pipes irradiated by electron beams
    • 10.1088/0031-9155/37/4/007
    • A. S. Beddar, T. R. Mackie, and F. H. Attix, " Cerenkov light generated in optical fibres and other light pipes irradiated by electron beams.," Phys. Med. Biol. 37, 925-935 (1992). 10.1088/0031-9155/37/4/007
    • (1992) Phys. Med. Biol. , vol.37 , pp. 925-935
    • Beddar, A.S.1    MacKie, T.R.2    Attix, F.H.3
  • 29
    • 0027219790 scopus 로고
    • Optical filtering and spectral measurements of radiation-induced light in plastic scintillation dosimetry
    • S. F. de Boer, A. S. Beddar, and J. A. Rawlinson, " Optical filtering and spectral measurements of radiation-induced light in plastic scintillation dosimetry.," Phys. Med. Biol. 38, 945-958 (1993). 10.1088/0031-9155/38/7/005 (Pubitemid 23222821)
    • (1993) Physics in Medicine and Biology , vol.38 , Issue.7 , pp. 945-958
    • De Boer, S.F.1    Beddar, A.S.2    Rawlinson, J.A.3
  • 30
    • 0026804696 scopus 로고
    • Water-equivalent plastic scintillation detectors for high-energy beam dosimetry. I. Physical characteristics and theoretical considerations
    • 10.1088/0031-9155/37/10/006
    • A. S. Beddar, T. R. Mackie, and F. H. Attix, " Water-equivalent plastic scintillation detectors for high-energy beam dosimetry. I. Physical characteristics and theoretical considerations.," Phys. Med. Biol. 37, 1883-1900 (1992). 10.1088/0031-9155/37/10/006
    • (1992) Phys. Med. Biol. , vol.37 , pp. 1883-1900
    • Beddar, A.S.1    MacKie, T.R.2    Attix, F.H.3
  • 33
    • 79953670862 scopus 로고    scopus 로고
    • Spectral method for the correction of the Cerenkov light effect in plastic scintillation detectors: A comparison study of calibration procedures and validation in Cerenkov light-dominated situations
    • 10.1118/1.3562896
    • M. Guillot, L. Gingras, L. Archambault, S. Beddar, and L. Beaulieu, " Spectral method for the correction of the Cerenkov light effect in plastic scintillation detectors: A comparison study of calibration procedures and validation in Cerenkov light-dominated situations.," Med. Phys. 38, 2140-2150 (2011). 10.1118/1.3562896
    • (2011) Med. Phys. , vol.38 , pp. 2140-2150
    • Guillot, M.1    Gingras, L.2    Archambault, L.3    Beddar, S.4    Beaulieu, L.5
  • 34
    • 0029713057 scopus 로고    scopus 로고
    • Evaluation of ruby as a fluorescent sensor for optical fiber-based radiation dosimetry
    • 10.1117/12.236190
    • K. J. Jordan, " Evaluation of ruby as a fluorescent sensor for optical fiber-based radiation dosimetry.," Proc. SPIE 2705, 170-178 (1996). 10.1117/12.236190
    • (1996) Proc. SPIE , vol.2705 , pp. 170-178
    • Jordan, K.J.1
  • 35
    • 0037149989 scopus 로고    scopus 로고
    • A temporal method of avoiding the Cerenkov radiation generated in organic scintillator dosimeters by pulsed mega-voltage electron and photon beams
    • DOI 10.1088/0031-9155/47/8/313, PII S0031915502313083
    • M. A. Clift, P. N. Johnston, and D. V. Webb, " A temporal method of avoiding the Cerenkov radiation generated in organic scintillator dosimeters by pulsed mega-voltage electron and photon beams.," Phys. Med. Biol. 47, 1421-1433 (2002). 10.1088/0031-9155/47/8/313 (Pubitemid 34495634)
    • (2002) Physics in Medicine and Biology , vol.47 , Issue.8 , pp. 1421-1433
    • Clift, M.A.1    Johnston, P.N.2    Webb, D.V.3
  • 36
    • 70049102550 scopus 로고    scopus 로고
    • Application of a Monte Carlo-based method for total scatter factors of small beams to new solid state micro-detectors
    • P. Francescon, S. Cora, C. Cavedon, and P. Scalchi, " Application of a Monte Carlo-based method for total scatter factors of small beams to new solid state micro-detectors.," J. Appl. Clin. Med. Phys. 10, 147-152 (2009).
    • (2009) J. Appl. Clin. Med. Phys. , vol.10 , pp. 147-152
    • Francescon, P.1    Cora, S.2    Cavedon, C.3    Scalchi, P.4
  • 37
    • 82755163844 scopus 로고    scopus 로고
    • sr for several small detectors and for two linear accelerators using Monte Carlo simulations
    • 10.1118/1.3660770
    • sr for several small detectors and for two linear accelerators using Monte Carlo simulations.," Med. Phys. 38, 6513-6527 (2011). 10.1118/1.3660770
    • (2011) Med. Phys. , vol.38 , pp. 6513-6527
    • Francescon, P.1    Cora, S.2    Satariano, N.3
  • 38
    • 84862001085 scopus 로고    scopus 로고
    • Monte Carlo simulated correction factors for machine specific reference field dose calibration and output factor measurement using fixed and iris collimators on the CyberKnife system
    • 10.1088/0031-9155/57/12/3741
    • P. Francescon, W. Kilby, N. Satariano, and S. Cora, " Monte Carlo simulated correction factors for machine specific reference field dose calibration and output factor measurement using fixed and iris collimators on the CyberKnife system.," Phys. Med. Biol. 57, 3741-3758 (2012). 10.1088/0031-9155/57/12/3741
    • (2012) Phys. Med. Biol. , vol.57 , pp. 3741-3758
    • Francescon, P.1    Kilby, W.2    Satariano, N.3    Cora, S.4
  • 39
    • 79960214850 scopus 로고    scopus 로고
    • Experimental comparison of seven commercial dosimetry diodes for measurement of stereotactic radiosurgery cone factors
    • 10.1118/1.3592647
    • S. Dieterich and G. W. Sherouse, " Experimental comparison of seven commercial dosimetry diodes for measurement of stereotactic radiosurgery cone factors.," Med. Phys. 38, 4166-4173 (2011). 10.1118/1.3592647
    • (2011) Med. Phys. , vol.38 , pp. 4166-4173
    • Dieterich, S.1    Sherouse, G.W.2
  • 40
    • 80053606968 scopus 로고    scopus 로고
    • Extraction of depth-dependent perturbation factors for silicon diodes using a plastic scintillation detector
    • 10.1118/1.3637496
    • F. Lacroix, M. Guillot, M. McEwen, L. Gingras, and L. Beaulieu, " Extraction of depth-dependent perturbation factors for silicon diodes using a plastic scintillation detector.," Med. Phys. 38, 5441-5447 (2011). 10.1118/1.3637496
    • (2011) Med. Phys. , vol.38 , pp. 5441-5447
    • Lacroix, F.1    Guillot, M.2    McEwen, M.3    Gingras, L.4    Beaulieu, L.5
  • 41
    • 70149094151 scopus 로고    scopus 로고
    • Determining charge collection efficiency in parallel-plate liquid ionization chambers
    • 10.1088/0031-9155/54/12/005
    • J. Pardo-Montero and F. Gomez, " Determining charge collection efficiency in parallel-plate liquid ionization chambers.," Phys. Med. Biol. 54, 3677-3689 (2009). 10.1088/0031-9155/54/12/005
    • (2009) Phys. Med. Biol. , vol.54 , pp. 3677-3689
    • Pardo-Montero, J.1    Gomez, F.2
  • 43
    • 84860209844 scopus 로고    scopus 로고
    • Small field diode correction factors derived using an air core fibre optic scintillation dosimeter and EBT2 film
    • 10.1088/0031-9155/57/9/2587
    • A. Ralston, P. Liu, K. Warrener, D. McKenzie, and N. Suchowerska, " Small field diode correction factors derived using an air core fibre optic scintillation dosimeter and EBT2 film.," Phys. Med. Biol. 57, 2587-2602 (2012). 10.1088/0031-9155/57/9/2587
    • (2012) Phys. Med. Biol. , vol.57 , pp. 2587-2602
    • Ralston, A.1    Liu, P.2    Warrener, K.3    McKenzie, D.4    Suchowerska, N.5


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