Author: Nicole C. Detorie, Steven M. Kirsner, Remy Y. Manigold 👨🔬
Affiliation: Scripps Cancer Center 🌍
Purpose:
Dosimetric Leaf Gap (DLG) is an important factor in obtaining the proper beam model in the Eclipse treatment planning system. The purpose of this study was to investigate the dosimetric impact on treatment plans and patient specific QA, when altering the standard DLG used for modeling. This establishes standards for DLG QA testing and beam matching.
Methods:
To evaluate the dosimetric impact of varying the DLG, 10 lung SBRT cases, 10 head and neck (H&N) cases, and 10 multi-met single isocenter SBRT brain met cases were recalculated with differing DLG values of ±0.2 to ±0.5mm of the standard DLG. Multiple relevant dosimetric criteria for all targets were compared. In addition, clinically relevant Organs at Risk (OAR) doses for each site were compared. Dose differences within 3% were deemed acceptable. QA results must pass within the standard criteria set by our department.
Results:
All lung SBRT cases targets and OARs were within 3% of the baseline plan with a DLG value ± 0.2 mm. All H&N case targets and OARs were within 3% of the baseline plan with a DLG value ± 0.2 mm. All SBRT brain met case targets and OARs were within 3% of the baseline plan with a DLG value ± 0.2 mm. QA pass rates were within standard passing criteria utilizing ± 0.2 mm.
Conclusion:
The results obtained from this study indicate that differences in DLG that are within 0.2 mm of the baseline DLG has no significant dosimetric impact on plans or patient specific QA. Therefore, we believe that 0.2 mm can be used as the criteria for annual DLG testing and beam matching between accelerators. This should be verified for one’s specific linear accelerators and treatment planning systems.