Impact of Flattening Filter On Output Correction Factor of MicroDiamond Detector in Small-Field Stereotactic Radiosurgery Beams
Y Arai*1, 2, Y Sato1, 3, T Takizawa1, 2, K Fujii1, K Yasui1, 2, K Sakai1, 2, M Sato1, Y Nakajima1, 2, Y Fujita1, (1) Komazawa University, Setagaya-ku, Tokyo, Japan, (2) Tokyo Metropolitan Cancer and Infectious Diseases Center Komagome Hospital, Bunkyo-ku, Tokyo, Japan, (3) Tokyo Medical and Dental University, Bunkyo-ku, Tokyo, Japan
Presentations
PO-GePV-T-365 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
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Purpose: The PTW 60019 microDiamond (mD) detector is close to an ideal detector for small-field dosimetry, such as stereotactic cones. Previous studies have reported differences in the energy dependence from the TRS-483 correction factors in terms of the output ratios between with-flattening-filter (WFF) and flattening-filter-free (FFF) beams. However, the impact of the flattening filter on the correction factors of the mD detector remains unclear. This study investigates the influence of the flattening filter on the output correction factor of the mD detector.
Methods: The analysis was performed on 6 and 10 MV (6X, 6FFF, 10X, 10FFF) using a Varian TrueBeam linac using 4–17.5 mm diameter Varian stereotactic radiosurgery (SRS) cones. The ratio of detector readings was obtained for each field size of the SRS cone. Moreover, the ratio of dose to water was estimated with a similar geometry using the Monte Carlo (MC) simulation. The output correction factors were determined by combining experimental measurements with the SRS cones and MC simulation as references, and the correction factor was calculated as the ratio of “ratio of dose to water” to “ratio of detector readings.”
Results: The relative difference between the WFF and FFF beams increased as the SRS cone diameter decreased. Additionally, the maximum relative difference between the 6 and 10 MV WFF and FFF beams for the output correction factors were 2% (4 mm) and 1% (4 mm), respectively. For a 4 mm diameter, the uncertainty (k = 2) for 6X, 6FFF, 10X, and 10FFF conditions were 1.4%, 1.3%, 0.9%, and 1.5%, respectively.
Conclusion: In small fields for stereotactic radiosurgery, the output correction factors for mD detectors indicated variations between the WFF and FFF beams; however, the estimated uncertainty is considerable, and it is essential to explore the causes of the deviation in the future.
Keywords
Small Fields, Dosimetry, Flattening Filters
Taxonomy
TH- External Beam- Photons: Small field experimental dosimetry
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