Author: Thomas R. Mazur, Kevin Renick, Matthew C. Schmidt, Xiaodong Neo Zhao 👨🔬
Affiliation: Washington University in St. Louis School of Medicine, Washington University School of Medicine 🌍
Purpose: To compare dose calculation accuracy for single-isocenter multi-target stereotactic radiosurgery plans (SIMT-SRS) in Eclipse V18.0 with enhanced leaf model (ELM) using the anisotropic analytical algorithm (AAA) to V15.6.06 AAA with user-defined dosimetric leaf gap (DLG) and transmission (Varian Medical Systems, Palo Alto, USA).
Methods: 36 SIMT-SRS patients previously treated on a Varian Edge with HDMLC and planned with V15.6.06 AAA (denoted AAA_DLG) were recalculated with V18.0 and ELM (denoted AAA_ELM). The following metrics were compared: D99%(%), D95%(%), Dmax(%), Dmin(%) for both the largest and smallest PTVs and GTVs, V12Gy(cc) for Brain-GTV, and Dmax(%) for Body. 10 patient-specific quality assurance (PSQA) plans of ion chamber in solid water were recalculated in V18. 5 used a PTW Semiflex 31010, while 5 used an Exradin A16. Re-calculated mean contour volume dose was compared to the measurement.
Results: All dose metrics evaluated showed systematic increases with AAA_ELM compared to AAA_DLG. For the largest targets, the median difference from AAA_DLG to AAA_ELM among all metrics increased from 2.10% (Dmin [ -1.00%, 3.70%]) to 2.40% (Dmax [-0.90%, 4.20%]) for GTVs and 1.80% (Dmin [0.00%, 6.50%]) to 2.40% (Dmax [0.00%, 4.10%]) for PTVs. For the smallest targets, AAA_ELM produced even greater increases, with median differences of 2.85% (Dmin [0.00%, 4.70%]) to 3.00% (Dmax [0.00%, 6.10%]) for GTVs and 2.15% (Dmin [0.00%, 4.90%]) to 3.20% (Dmax [0.00%, 6.10%]) for PTVs. In ion chamber analysis, V18.0 showed an average increase in the expected dose of 2.24% ± 1.22% for the A16 and 1.67% ± 0.28% for the PTW 31010. Across both, the average percent difference of expected-to-measured agreement increased by 1.57% ± 0.89%.
Conclusion: The AAA dose calculated with enhanced leaf modeling in v18.0 showed a systematically hotter expected dose than AAA v15.6.06. The agreement to measurement needs further investigation with other small field equipment.