Dosimetric characterization of CyberKnife radiosurgical photon beams using polymer gels

Authors

  • Pantelis E.,

    1. Medical Physics Department, Iatropolis — Magnitiki Tomografia Clinic and Diagnostic Center, Ethnikis Antistaseos 54-56, Chalandri, 152 31, Athens, Greece
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  • Antypas C.,

    1. Medical Physics Department, Iatropolis — Magnitiki Tomografia Clinic and Diagnostic Center, Ethnikis Antistaseos 54-56, Chalandri, 152 31, Athens, Greece
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  • Petrokokkinos L.,

    1. Nuclear and Particle Physics Section, Physics Department, University of Athens, Panepistimioupolis, Ilisia, 157 71 Athens, Greece and Institute of Accelerating Systems & Applications (IASA), PO Box 17214, GR-10024 Athens, Greece
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  • Karaiskos P.,

    1. Medical Physics Laboratory, Medical School, University of Athens, 75 Mikras Asias, 115 27 Athens, Greece
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  • Papagiannis P.,

    1. Medical Physics Laboratory, Medical School, University of Athens, 75 Mikras Asias, 115 27 Athens, Greece
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  • Kozicki M.,

    1. Faculty of Textile Engineering and Marketing, Department of Textile Finishing, Technical University of Lodz, Zeromskiego 116, 90-543 Lodz, Poland
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  • Georgiou E.,

    1. Medical Physics Laboratory, Medical School, University of Athens, 75 Mikras Asias, 115 27 Athens, Greece
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  • Sakelliou L.,

    1. Nuclear and Particle Physics Section, Physics Department, University of Athens, Panepistimioupolis, Ilisia, 157 71 Athens, Greece and Institute of Accelerating Systems & Applications (IASA), PO Box 17214, GR-10024 Athens, Greece
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  • Seimenis I.

    1. Medical Diagnostic Center Ayios Therissos, 92 Troodous Avenue, Strovolos, Nicosia, Cyprus
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Abstract

Dose distributions registered in water equivalent, polymer gel dosimeters were used to measure the output factors and off-axis profiles of the radiosurgical photon beams employed for CyberKnife radiosurgery. Corresponding measurements were also performed using a shielded silicon diode commonly employed for CyberKnife commissioning, the PinPoint ion chamber, and Gafchromic EBT films, for reasons of comparison. Polymer gel results of this work for the output factors of the 5, 7.5, and 10 mm diameter beams are (0.702±0.029), (0.872±0.039), and (0.929±0.041), respectively. Comparison of polymer gel and diode measurements shows that the latter overestimate output factors of the two small beams (5% for the 5 mm beam and 3% for the 7.5 mm beams). This is attributed to the nonwater equivalence of the high atomic number silicon material of the diode detector. On the other hand, the PinPoint chamber is found to underestimate output factors up to 10% for the 5 mm beam due to volume averaging effects. Polymer gel and EBT film output factor results are found in close agreement for all beam sizes, emphasizing the importance of water equivalence and fine detector sensitive volume for small field dosimetry. Relative off-axis profile results are in good agreement for all dosimeters used in this work, with noticeable differences observed only in the PinPoint estimate of the 80%20% penumbra width, which is relatively overestimated.

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