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Scintillator Optical Imaging for Co-60 Irradiator Quality Assurance Testing

I Tendler1*, J Bredfeldt2, R Zhang3 , P Bruza1 , M Jermyn1, B Pogue1,4,5 , D Gladstone1,5,6, (1) Thayer School of Engineering, Dartmouth College, Hanover, NH, (2) Brigham and Women's Hospital, Boston, MA (3) Emory Proton Therapy Center, Johns Creek, GA, (4) DoseOptics LLC, Lebanon, NH, (5) Dept. of Medicine, Geisel School of Medicine, Dartmouth College, Hanover, NH (6) Norris Cotton Cancer Center, Dartmouth-Hitchcock Med. Ctr., Lebanon, NH,


(Sunday, 7/14/2019)  

Room: ePoster Forums

Purpose: To create an optical imaging-based system for quality assurance (QA) testing of a Co-60 Total Body Irradiation (TBI) machine. We envision that implementation of this system will streamline QA by reducing the amount of time necessary to conduct tests such as verification of field homogeneity and symmetry.

Methods: Custom-machined plastic rods (8 x 15 x 1000 mm) were placed on the patient treatment couch of a dedicated TBI Co-60 irradiator. An intensified camera was positioned directly adjacent to the couch; image acquisition was started manually once the source was fully exposed and continued for 30 seconds. Data was filtered in real-time, cumulative images were background subtracted and flatfield corrected. Scintillators were used to measure dose rate, light-radiation field correspondence, field homogeneity and symmetry. Dose rate was changed by modifying SSD and scintillator signal was compared to ionization chamber (IC) measurements. Field symmetry and homogeneity scintillator data were compared to OSLD measurements.

Results: Scintillator imaging was able to accurately report changes in dose rate; normalized output values for IC versus scintillators over various SSDs yields a linear relationship, R² = 0.99. The light field was found to correspond to 90 ± 3% of the isodose maximum along the longitudinal and latitudinal axis, respectively. Beam symmetry across both axes of the field was within 2%. Scintillators showed that in the region of the lightfield, the beam was 2.3 ± 0.5% homogeneous. Normalized scintillator readings matched OSLD measurements with <1.5% difference. Scintillator imaging provided results with a single image stack, no post-exposure processing (OSLD) or repeat manual measurements (IC) were necessary.

Conclusion: We have shown that scintillator imaging is a viable and efficient method for conducting TBI Co-60 irradiator QA. This technique has successfully and accurately measured field homogeneity, symmetry, dose rate effects, and light-radiation field correspondence.

Funding Support, Disclosures, and Conflict of Interest: Michael Jermyn is an employee and Brian Pogue is a president of DoseOptics LLC. Petr Bruza is the principal investigator in SBIR subaward B02463 (prime award NCI R44CA199681, DoseOptics LLC).


Scintillators, Quality Assurance, Quantitative Imaging


TH- External beam- photons: Development (new technology and techniques)

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