ESTRO 2024 - Abstract Book

S4914

Physics - Quality assurance and auditing

ESTRO 2024

Results:

The new workflow for Iris QA proved to be sensitive for the field size tolerance of 0.2 mm specified by Accuray [1], as statistical deviations in the field size of 0.1 mm could be detected. Measurements of flatness and symmetry of the beam were consistent with recorded data. The new MLC QA resulted mean deviations of the leaf positions from their nominal positions of 0.12 mm or smaller for all MLC leaves evaluated, showing that errors exceeding the criterion of 0.5 mm [1] can be reliably detected. The systematic trend with larger deviation being detected in the outer stripes, which has been observed in previous film measurements, could also be confirmed with the new QA method. Shifts introduced to test the new QA method were all detected with a mean deviation of 0.12 mm, the maximal deviation being 0.36 mm. The specified tolerance for AQA tests is a radial deviation from a baseline value smaller than 0.95 mm [1], however current practice at the University Hospital Heidelberg is to reduce the tolerance to 0.65 mm. With the new AQA test resulting in radial standard deviations of the baseline values of 0.14 mm, 0.12 mm and 0.14 mm for fixed, Iris collimator and MLC respectively, the new workflow proves suitable to detect exceeded tolerances. The mean deviations between nominal introduced shift and measured shift were 0.11 mm, 0.02 mm and 0.01 mm in x-, y- and z-direction, promoting the sensitivity of the implemented workflow.

Conclusion:

The new workflows for Iris QA, Bayouth test for MLC QA and the AQA test were in all cases sensitive enough to guarantee stable QA. Through the digital workflow the execution of the QA measurements and data analysis was considerably simplified. The new experiment setup reduces the time needed for CyberKnife QA as well as the probability for errors due to handling difficulties.

Keywords: Stereotactic radiosurgery, machine QA

References:

[1] Accuray Incorporated, Physics Essentials Guide. CyberKnife® Treatment Delivery System. 2018

[2] Dieterich S, Cavedon C, Chuang CF, et al, Report of AAPM TG 135: quality assurance for robotic radiosurgery. Med. Phys. Vol 38(6), 2011

[3] http://www.gafchromic.com/, accessed October 2023

[4] Niroomand-Rad A et al., Report of AAPM Task Group 235 Radiochromic Film Dosimetry: An Update to TG-55. Med. Phys. Vol 47, 2020

[5] Padelli F. et al., IBA myQA SRS Detector for CyberKnife Robotic Radiosurgery Quality Assurance. Appl. Sci., 2022

[6] Bayouth JE et al., MLC quality assurance techniques for IMRT applications . Med. Phys. Vol 30(5), 2003