Author: Elizabeth M. Alves, Alistair K. Templeton, Julius V. Turian 👨🔬
Affiliation: Rush University Medical Center 🌍
Purpose: To test the performance of two similar, but not beam-matched, linacs in interchangeably delivering IMRT and VMAT patient-specific quality assurance (PSQA) tests.
Methods: Two TrueBeam linacs (TrueBeam1, TB1; TrueBream2, TB2) were accepted and commissioned by separate groups of physicists at our institution. Calculated doses for TB1 were compared in a gamma analysis of variable levels (3%/3 mm, 2%/2 mm, 1%/1 mm) against a measured dose for TB2, and vice versa. The results of the cross-machine gamma analyses underwent paired t-tests to determine if there is a statistical significance between doses measured on the linac the plan was optimized on versus if delivered on the similar, but not beam-matched linac.
Results: Plans optimized on TB1 (n=9) and TB2 (n=17) underwent PSQA on the machine they were optimized on and on the similar but not beam-matched linac. The results of a paired t-test showed that the gamma passing rates between the not beam-matched linacs were not significant (3%/3 mm, p=0.4358; 2%/2 mm, p=0.0835; 1%/1 mm, p=0.0531) when using the calculated doses from the linac the plan was optimized on. Modifying to the calculated dose to reflect the not beam-matched linac also did not yield statistically significant results (3%/3 mm, p= 0.1539; 2%/2 mm, p=0.1143; 1%/1 mm, p=0.1383).
Conclusion: Despite not having beam-matched linacs, PSQA tests can be performed interchangeably between TB1 and TB2 within our clinic as the gamma analyses are not statistically different.