Stereotactic detector comparisons for small field relative dosimetry
G. Johnson,1 C. Malmer,1 B. Owen,1 J. Garci-Cobian,1 S. Small,1 D. King,2 D. Siergiej3
1Northwest Medical Physics Center, Lynnwood, WA; 2Madigan Army Medical Center, Joint Base Lewis-McChord, WA; 3University of New Mexico, Albuquerque, NM
AAPM Annual Scientific Meeting, Nashville, TN (2018).
Purpose: To investigate different detectors for relative dosimetry of small fields using a traditional linear accelerator and following the International Atomic Energy Agency (IAEA) Code of Practice (COP) Report No. 483 published in 2017.
Methods: Four detectors were investigated including the Sun Nuclear Edge, IBA Dosimetry Razor, Standard Imaging Exradin A16, and the PTW microDiamond. An IBA Stealth Chamber was used as the reference detector for profiles and depth curves. The measurements were made on a linac with photon energies of 6MV, 6MV SRS, and 10MV. A three-dimensional water phantom was used to take measurements of square field sizes down to 0.5 cm x 0.5 cm, including PDD curves at SSD 100cm, as well as profiles and output factors at a depth of 10cm, 90cm SSD. All output factors were daisy chained at 4cm to an IBA CC13 chamber. Correction factors were applied as stated in the COP.
Results: The difference from average for the uncorrected and corrected output factors were -0.87% and 0.48% for the Edge, 0.60% and -1.01% for the Razor, -0.43% and 0.30% for the microDiamond, and 0.94% and 0.52% for the A16, respectively. From the PDD curves, the difference from average for the d20/d10 ratio was 0.94% for the Edge, 0.26% for the Razor, 0.29% for the microDiamond, and 0.93% for the A16. From the profiles, the difference from average FWHM was 0.76% for the Edge, 0.78% for the Razor, 0.51% for the microDiamond, and 0.98% for the A16.
Conclusion: All the data was found to be within 1.01% different from average. Corrected output factors converged for all detectors, except the Razor. This study shows that any of the four detectors can be used to measure small field relative dosimetry within clinically acceptable deviation for stereotactic applications.