Author: Juan-Francisco Calvo-Ortega, Andrew Cousins, Ashley Cullen, Andrew Dipulia, Peter B. Greer, Seng Boh Gary Lim, Shih-Chi Lin, D. Michael Lovelock, Conor McGarry, Victoria Robinson, Cameron Stanton, Baozhou Sun, Ching-Ling Teng, Gemma Warner, Benjamin J. Zwan 👨🔬
Affiliation: Northern Ireland Cancer Centre, Baylor College of Medicine, Department of Medical Physics, Memorial Sloan Kettering Cancer Center, Christchurch Hospital, Northwell, Central Coast Cancer Centre, Calvary Mater Hospital, Hospital Quironsalud Barcelona, Icahn School of Medicine at Mount Sinai, Chris O'Brien Lifehouse, University of Newcastle 🌍
Purpose: This multi-institution Electronic Silicon-based Remote Survey of Small-field Output (ESPRESSO) study aims to develop the remote audit process to evaluate the safety of single-isocenter multi-target stereotactic radiosurgery (SRS) delivery globally without specialized equipment.
Methods: Eight international institutions from North America, Europe, and Australia participated in this study. All participants used the Varian TrueBeam with HD120 and the Eclipse Treatment Planning System (TPS). The dosimetric leaf gap (DLG) for each machine (DLG_M) was measured with an ionization chamber at 10cm depth and SAD 100cm; the corresponding DLG for each TPS (DLG_TPS) was recorded. The multi-leaf collimator (MLC) offset (MLC_offset) was determined by calculating the difference between the 5x5mm2 MLC opening size, as measured with an electronic portal imaging device (EPID), and the nominal size. The parameters for the TPS focal spot (TPS_FS) and MLC transmission (MLC_trans) were gathered from each institution. Spearman's correlations were used to assess the relationships among the parameters. The 3D-dose estimated in a virtual 20cm-diameter spherical phantom with an EPID-based method were compared to the TPS calculation at three pilot sites using gamma analysis criteria of ϒ(3%/2mm/10%), ϒ(5%/1mm/10%), and ϒ(3%/1mm/30%).
Results: Significant correlations were found for DLG_M/DLG_TPS (p-value = 0.049), DLG_M/MLC _offset_X (p-value < 0.001), and DLG_TPS/MLC_offset_X (p-value < 0.001) with correlation factors of 1.26, 1.52, and 2.46 respectively. The correlations between TPS_FS and MLC_trans with DLG_M and DLG_TPS were insignificant. 523 SRS cases were measured at three pilot institutions. The average gamma scores were 99.9%, 99.9%, and 96.4% for ϒ(3%/2mm/10%), ϒ(5%/1mm/10%), and ϒ(3%/1mm/30%). The corresponding standard deviation and minimum scores were (0.9%, 81.3%), (0.9%, 80.4%), and (4.7%, 59.3%).
Conclusion: Significant correlations were observed between DLG_M and DLG_TPS with the MLC opening. More data will be recruited to establish the relationship of TPS DLG with gamma variation to demonstrate the feasibility of remote SRS credentialing.