Investigation of a Commercial OSLD System for CT Dosimetry
S Scarboro1,2*, D Cody1,2, D Followill1,2, P Alvarez1, M McNitt-Gray3, D Zhang3, L Court1,2, S Kry1,2, (1) UT MD Anderson Cancer Center, Houston, TX, (2) UT Health Science Center Graduate School of Biomedical Sciences, Houston, TX, (3) UCLA School of Medicine, Los Angeles, CATU-G-217BCD-1 Tuesday 4:30:00 PM - 6:00:00 PM Room: 217BCD
Purpose: With an increasing use of computed tomography (CT) in diagnostic procedures, there is a growing need for more accurate and patient-specific dosimetry techniques. Optically stimulated luminescent dosimetry (OSLD), well-suited for in-vivo dosimetry with little if any impact on diagnostic image quality, offers a potential solution. We have characterized a commercially available OSLD system, provided CT calibration protocols, quantified uncertainties, and tested the system against ion chamber measurements for various CT applications.
Methods: Landauer nanoDots were fully characterized through both measurements and theoretical approaches to quantify the effects of dose linearity, signal depletion, fading, angular dependence, and energy dependence specific to a CT environment. Three calibration approaches that included calibration (1) relative to a 60Co source, (2) relative to a 120kVp CT spectrum in air, and (3) using the vendor provided method were investigated along with their associated uncertainty. The OSL system and calibration procedures were tested and compared to ion chamber measurements using standard CTDI phantoms. The defined calibration protocols were used to measure an anthropomorphic head phantom's lens dose.
Results: We determined the OSLD characteristics and calibration techniques appropriate for CT dosimetry. Most correction factors were less than 5% with the exception of energy dependence which, depending on the calibration method and specific scan parameters, was as large as 400% due to the OSL over-response at low energies. The uncertainty budget for the dose calculations showed the uncertainties (2-sigma) to range from 11% to 20% for a properly corrected system. More rigorous calibration approaches resulted in lower dosimetric uncertainties.
Conclusion: The OSLD calibration protocols and correction factors described provide a precise and accurate patient dosimetry and documentation method for routine monitoring of CT patients, as well as for special procedures such as CT perfusion.