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SU‐F‐T‐460: Dosimetric Matching Between Trilogy Tx and TrueBeam STx
Author(s) -
Choi Y,
Kwak J,
Jeong C,
Ahn S,
Lee S,
Cho B
Publication year - 2016
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4956645
Subject(s) - truebeam , optics , nuclear medicine , ionization chamber , linear particle accelerator , beam (structure) , imaging phantom , physics , materials science , medicine , ion , ionization , quantum mechanics
Purpose: To compare the commissioned beam data for one flattening filter photon mode (6 MV) and two flattening filter‐free (FFF) photon modes (6 and 10 MV‐FFF) between Trilogy Tx and TrueBeam STx and evaluate the possibility of dosimetric matching Methods: Dosimetric characteristics of the new Trilogy Tx including percent depth doses (PDDs), profiles, and output factors were measured for commissioning. Linear diode array detector and ion chambers were used to measure dosimetric data. The depth of dose maximum (dmax) and PDD at 10 cm (PDD10) were evaluated: 3×3 cm 2 , 10×10 cm 2 , and 40×40 cm 2 . The beam profiles were compared and then penumbras were evaluated. As a further test of the dosimetric matching, the same VMAT plans were delivered, measured with film, and compared with TPS calculation. Results: All the measured PDDs matched well across the two units. PDD10 showed less than 0.5% variation and dmax were within 1.5 mm at the field sizes evaluated. Within the central 80% of transverse axis, profile data were almost identical. TrueBeam data resulted in a slightly greater penumbra width (up to 1.9 mm). The greatest differences of output factors were found at 40 × 40 cm 2 : 2.40%, 2.03%, and 2.22% for 6 MV, 6 MV‐FFF, and 10 MV‐FFF, respectively. For smaller field sizes, less than 1% differences were observed. The film measurements demonstrated over 97.3% pixels passing‐gamma analysis (2%/2mm). The results showed excellent agreement between measurements of two machines. Conclusion: The differences between Trilogy Tx and TrueBeam STx found could possibly affect small field and also very large field sizes in dosimetric matching considerations. These differences encountered are mostly related with the changes in the head design of the TrueBeam. Although it cannot guarantee full interchangeability of two machines, dosimetric matching by field size of 25 × 25 cm 2 might be clinically acceptable.

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