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SU‐F‐T‐324: Experimental Measurement of Optically Stimulated Luminescence Detectors in a MR‐IGRT Environment Toward Assessing Magnetic Field Effects On These Devices and Their Use as An In‐Vivo Dosimeter
Author(s) -
Reilly M,
Curcuru A,
Yaddanapudi S,
Green O
Publication year - 2016
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4956509
Subject(s) - dosimeter , magnetic field , optics , perpendicular , image guided radiation therapy , magnetostatics , materials science , detector , beam (structure) , imaging phantom , physics , nuclear magnetic resonance , radiation , medical imaging , medicine , geometry , mathematics , quantum mechanics , radiology
Purpose: To characterize magnetic field effects on Optically Stimulated Luminescence Detectors (OSLDs) for use as an in‐vivo dosimeter in an MRIGRT machine. Methods: Landauer OSLD nano‐dots and the MicroStar II reader were used to measure and record OSLDs exposed in and on a solid water phantom in a 10.5 × 10.5 cm 2 field, Co‐60, 0.32‐Tesla MR‐IGRT machine ‐ with and without the presence of the magnetic field. Two orthogonal gantry angles were considered to assess orientation effects on the OSLDs with respect to the incident angle of the radiation beam and magnetic field. The same OSLDs were then used (after readout and bleaching) when the magnetic field was restored. Results: The measured surface dose decreased by 14.1 ± 1.8% when magnetic field was 'on’ due to contamination electrons being swept away by the field. Doses at both 0.5 cm and 5 cm depth increased by 6.5 ± 0.9% and 8.8 ± 0.5% respectively when the magnetic field was present and the OSLDs oriented with their long axis parallel with the incident beam. This contrasts with an increased dose of 2.7 ± 1.1% when the magnetic field was present and the OSLDs were oriented with their long axis perpendicular to the incident beam. Conclusion: Previous works have shown that OSLDs have a dependence on beam incidence angle. Our current work suggests an additional dependence on the presence of the magnetic field when the beam is not perpendicular to the plane of the detector and this effect needs to be considered. Furthermore, the use of an in‐vivo dosimeter was shown to have no effect on image quality during the use of MR guidance. Future work will focus on the use of an electromagnet with a linear accelerator to further characterize these effects.