Room: Exhibit Hall
Purpose: To compare dosimetry of multi-isocenter plans using Eclipse V15.5 with photon optimizer and multi-isocenter grouping versus sum of two plans with Eclipse V13.6. Comparisons are done for two lung lesions: right lower lobe lateral PTV (PTV_lat) and right lower lobe medial PTV (PTV_med).
Methods: Two stereotactic body radiation therapy (SBRT) plans with 4D CT scans were created for each target in Eclipse V13.6. Each plan has two arcs with different isocenters and was optimized with various dose constraints for targets and organs-in-risk (OARs). The central distance between the two targets is 10.3 cm. Both targets were prescribed to 52.5 Gy in 5 fractions. After optimization, a composite plan (SUM-13.6) was created to equally sum the two plans. The same beam parameters were used and grouped into two isocenters in Eclipse V15.5. After optimization, this new plan (LAT-MED-15.5) was compared with SUM-13.6.
Results: In SUM-13.6, dose ranges of GTV_lat and PTV_lat are 134.6% ~147.4% and 95.5% ~147.4%. Dose ranges of GTV_med and PTV_med are 109.2% ~ 131.0% and 90.0% ~ 131.0%. In LAT-MED-15.5, dose ranges of GTV_lat and PTV_lat are 97% ~ 101.9% and 78.1% ~ 109.2%. Dose ranges of GTV_med and PTV_med are 96% ~ 103.5% and 87.4% ~ 103.9%. For heart, maximum and mean doses are reduced from 5.55 Gy and 0.83 Gy in SUM-13.6 to 4.87 Gy and 0.74 Gy in LAT-MED-15.5. For stomach, maximum and mean doses are reduced from 24.2 Gy and 11.8 Gy in SUM-13.6 to 23.6 Gy and 10.3 Gy in LAT-MED-15.5. For liver, maximum and mean doses are reduced from 74.8 Gy and 6.1 Gy in SUM-13.6 to 57.4 Gy and 5.8 Gy in LAT-MED-15.5.
Conclusion: Simultaneous multi-isocenter plans using Eclipse V15.5 yield improved PTV and OAR dosimetry compared to separate plans using Eclipse V13.6.