Abstract
Field junctions between megavoltage photon beams are important in modern radiotherapy for treatments such as head and neck and breast cancer. An electronic portal imaging device (EPID) may be used to study junction dose between two megavoltage X-ray fields. In this study, the junction dose was used to determine machine characteristics such as jaw positions and their reproducibility, collimator rotation and the effect of gantry rotation. All measurements were done on Varian linear accelerators with EPID (Varian, Palo Alto, CA). The results show reproducibility in jaw positions of approximately 0.3 mm for repeated jaw placement while EPID readings were reproducible within a standard deviation of 0.4% for fixed jaw positions. Junction dose also allowed collimator rotation error of 0.1° to be observed. Dependence of junction dose on gantry rotation due to gravity was observed; the gravity effect being maximum at 180° gantry angle (beam pointing up). EPIDs were found to be reliable tools for checking field junctions, which in turn may be used to check jaw reproducibility and collimator rotation of linacs.
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References
Antonuk LE (2002) Electronic portal imaging devices: a review and historical perspective of contemporary technologies and research. Phys Med Biol 47(6):R31–R65
Kirby MC, Williams PC (1995) The use of an electronic portal imaging device for exit dosimetry and quality control measurements. Int J Radiat Oncol Biol Phys 31:593–603
Liu G, van Doorn T, Bezak E (2002) Assessment of flatness and symmetry of megavoltage X-ray beam with an electronic portal imaging device (EPID). Australas Phys Eng Sci Med 25:58–66
Samant SS, Zheng W, Parra NA, Chandler J, Gopal A, Wu J, Jain J, Zhu Y, Sontag M (2002) Verification of multileaf collimator leaf positions using an electronic portal imaging device. Med Phys 29:2900–2912
Clarke MF, Budgell GJ (2008) Use of an amorphous silicon EPID for measuring MLC calibration at varying gantry angle. Phys Med Biol 53:473–485
Curtin-Savard A, Podgorsak EB (1997) An electronic portal imaging device as a physics tool. Med Dosim 22:101–105
Budgell GJ, Zhang R, Mackay RI (2007) Daily monitoring of linear accelerator beam parameters using an amorphous silicon EPID. Phys Med Biol 52:1721–1733
Vieira SC, Bolt RA, Dirkx ML, Visser AG, Heijmen BJ (2006) Fast, daily linac verification for segmented IMRT using electronic portal imaging. Radiother Oncol 80:86–92
Holmberg O, Huizenga H, Idzes MH, Lebesque JV, Vijlbrief RE, Mijnheer BJ (1994) In vivo determination of the accuracy of field matching in breast cancer irradiation using an electronic portal imaging device. Radiother Oncol 33:157–166
Greer PB, Barnes MP (2007) Investigation of an amorphous silicon EPID for measurement and quality assurance of enhanced dynamic wedge. Phys Med Biol 52:1075–1087
Van Esch A, Depuydt T, Huyskens DP (2004) The use of an aSi-based EPID for routine absolute dosimetric pre-treatment verification of dynamic IMRT fields. Radiother Oncol 71:223–234
van Zijtveld M, Dirkx ML, de Boer HC, Heijmen BJ (2006) Dosimetric pre-treatment verification of IMRT using an EPID; clinical experience. Radiother Oncol 81:168–175
Zeng GG, Heaton RK, Catton CN, Chung PW, O’Sullivan B, Lau M, Parent A, Jaffray DA (2007) A two isocentre IMRT technique with a controlled junction dose for long volume targets. Phys Med Biol 52:4541–4552
Rosenthal DI, McDonough J, Kassaee A (1998) The effect of independent collimator misalignment on the dosimetry of abutted half-beam blocked fields for the treatment of head and neck cancer. Radiother Oncol 49:273–278
Saw C, Krishna K, Enke C, Hussey D (2000) Dosimetric evaluation of abutted fields using asymmetric collimators for treatment of head and neck. Int J Radiat Oncol Biol Phys 47:821–824
Lee PC (1997) Consistent collimator overlaps in field matching with computer-controlled X-ray collimator. Med Dosim 22:59–61
Kron T, Barnes K, O’Brien P (2003) Multicentre dosimetric comparison of photon-junctioning techniques in head and neck radiotherapy. Australas Radiol 47(3):289–294
Kron T (2000) The potential for symmetric field placement errors when using asymmetric collimation for photon field junction. Australas Phys Eng Sci Med 23(2):58–60
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Madebo, M., Perkins, A., Fox, C. et al. Study of X-ray field junction dose using an a-Si electronic portal imaging device. Australas Phys Eng Sci Med 33, 45–50 (2010). https://doi.org/10.1007/s13246-010-0005-9
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DOI: https://doi.org/10.1007/s13246-010-0005-9