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Characterization of the Clinically Released ScandiDos Discover Diode Array for In-Vivo Dose Monitoring

D Saenz

D Saenz*, A Gutierrez , University of Texas Health Science Center San Antonio, San Antonio, TX


SU-F-T-330 (Sunday, July 31, 2016) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: The ScandiDos Discover has obtained FDA clearance and is now clinically released. We studied the essential attenuation and beam hardening components as well as tested the diode array’s ability to detect changes in absolute dose and MLC leaf positions.

Methods: The ScandiDos Discover was mounted on the heads of an Elekta VersaHD and a Varian 23EX. Beam attenuation measurements were made at 10 cm depth for 6 MV and 18 MV beam energies. The PDD(10) was measured as a metric for the effect on beam quality. Next, a plan consisting of two orthogonal 10 x 10 cm² fields was used to adjust the dose per fraction by scaling monitor units to test the absolute dose detection sensitivity of the Discover. A second plan (conformal arc) was then delivered several times independently on the Elekta VersaHD. Artificially introduced MLC position errors in the four central leaves were then added. The errors were incrementally increased from 1 mm to 4 mm and back across seven control points.

Results: The absolute dose measured at 10 cm depth decreased by 1.2% and 0.7% for 6 MV and 18 MV beam with the Discover, respectively. Attenuation depended slightly on the field size but only changed the attenuation by 0.1% across 5 x 5 cm² and 20 x 20 cm² fields. The change in PDD(10) for a 10 x 10 cm² field was +0.1% and +0.6% for 6 MV and 18 MV, respectively. Changes in monitor units from -5.0% to 5.0% were faithfully detected. Detected leaf errors were within 1.0 mm of intended errors.

Conclusion: A novel in-vivo dosimeter monitoring the radiation beam during treatment was examined through its attenuation and beam hardening characteristics. The device tracked with changes in absolute dose as well as introduced leaf position deviations.

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