ESTRO 2024 - Abstract Book

S4800

Physics - Quality assurance and auditing

ESTRO 2024

According to the linear fit, the optimal CO was 0.3mm (intersect of Δ and the x-axis). The WL and star shot results were also minimized using this CO value.

Interestingly, the optimal value for the CO parameter, which minimizes de Δ value, can be readily obtained from the obtained measurements and a single result of the proposed half-slit test. As it can be easily derived from the linear fit, the CO value to be shifted can be determined as:

Shift in CO = 0.6*Δ , where Δ=delta value obtained with the half-slit test.

These results were obtained using 6 MV, but they were verified for 6MV FFF and 10 MV FFF and better results were also been obtained for WL and Star shot. Consequently, the result of the calibration was valid regardless of the beam energy used.

Conclusion:

• The half-slit proposed method allows the calibration of the center offset parameter in TrueBeam accelerators with a precision better than 0.05mm. • Star shots and WL are the standard methods to evaluate isocenter rotations and differences between isocenters and they are both sensitive to differences in the MLC centerline position. • The proposed method is simpler than the others to determine the optimal MLC centerline position since it provides the optimal value using the proposed test and a single measurement (<10 min). • The method can be used independently of the MLC and LINAC model and the calibration was found to be valid for all energies.