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Impact of Multi-Leaf Collimator (MLC) Uncertainty on the Quality of Single-Isocenter Multi-Target Radiotherapy for Brain Tumors |
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PP: 217-223 |
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doi:10.18576/jrna/110304
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Author(s) |
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Khloud Ibrahim,
Khaled M. El-Shahat,
Sayed M. Awad,
Sarah M. Osman,
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Abstract |
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| o quantify the dosimetric and patient-specific quality assurance impact of multileaf collimator (MLC) positioning uncertainty in single-isocenter multi-target (SIMT) stereotactic radiotherapy for brain tumors.
Methods: A retrospective/simulation-based dataset of 25 patients with 62 intracranial targets treated with SIMT stereotactic radiosurgery or fractionated stereotactic radiotherapy was analyzed. Plans were generated in Eclipse, RayStation, and Monaco for TrueBeam STx, Varian Edge, and Elekta Versa HD platforms. Prescriptions ranged from 18 to 24 Gy in 1 to 3 fractions. Planned and delivered plan-quality indices, target coverage metrics, organ-at-risk doses, MLC tracking errors, and portal-dosimetry gamma pass rates at 3%/1 mm were extracted from the workbook. Paired planned-versus-delivered comparisons, Pearson correlation analysis, and simple linear regression were performed.
Results: The mean total MLC error was 0.62 ± 0.17 mm (range 0.25-0.90 mm). Delivered plans showed statistically significant degradation in conformity index (mean ΔCI 0.087), gradient index (mean ΔGI 0.45), homogeneity index (mean ΔHI 0.042), D95% (mean ΔD95% -2.33%), and D98% (mean ΔD98% -2.71%; all paired p<0.001). Total MLC error correlated with gamma pass rate (r=-0.67, p<0.001), ΔD95% (r=-0.46, p=0.022), and ΔGI (r=0.46, p=0.019). Regression estimated a 9.7% gamma-pass-rate decrease and 3.1% D95% loss per 1-mm increase in total MLC error.
Conclusion: MLC uncertainty in the 0.25-0.90 mm range measurably degraded target coverage, dose fall-off, and gamma pass rate in SIMT brain stereotactic treatments. The findings support stringent MLC commissioning, routine high-resolution MLC QA, and SIMT-specific patient QA rather than reliance on generic IMRT/VMAT tolerances alone. |
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