Top Line: How can lung SBRT plans be optimized to improve dose conformity and reduce OAR dose?
The Study: In this retrospective treatment planning study, 288 lung SBRT cases were replanned using a simple planning algorithm that required little user interaction. All replans used two 180 degree half-arcs with 6 MV FFF energy and a 45 degree collimator angle. The optimization had only two objectives: a lower objective for PTV coverage, and a normal tissue optimization (NTO) objective to drive the dose gradient surrounding the target. The NTO objective was set for a dose falloff rate of 0.15 starting from 100% of the prescribed dose down to 20%. The prescription was 50 Gy in 5 fractions, and the plans were normalized so that 50 Gy covered 95% of the PTV. Compared to the original clinically treated plans, the re-optimized plans had significantly lower conformity indices across target sizes and isodose levels evaluated. The most significant reductions in the conformity index were seen at lower isodose levels such as 20-30% of the prescription dose. This suggests significant reductions in low dose spill using the noncoplanar NTO optimization. Despite no OAR objectives being included in the re-optimized plans, these plans had significantly better sparing of the chest wall and lungs.
TBL: In this planning study, a simple, noncoplanar VMAT planning algorithm that optimized dose falloff around the target resulted in significantly better conformity and OAR sparing for lung SBRT plans. | Kei, Pract Radiat Oncol 2025
The Study: In this retrospective treatment planning study, 288 lung SBRT cases were replanned using a simple planning algorithm that required little user interaction. All replans used two 180 degree half-arcs with 6 MV FFF energy and a 45 degree collimator angle. The optimization had only two objectives: a lower objective for PTV coverage, and a normal tissue optimization (NTO) objective to drive the dose gradient surrounding the target. The NTO objective was set for a dose falloff rate of 0.15 starting from 100% of the prescribed dose down to 20%. The prescription was 50 Gy in 5 fractions, and the plans were normalized so that 50 Gy covered 95% of the PTV. Compared to the original clinically treated plans, the re-optimized plans had significantly lower conformity indices across target sizes and isodose levels evaluated. The most significant reductions in the conformity index were seen at lower isodose levels such as 20-30% of the prescription dose. This suggests significant reductions in low dose spill using the noncoplanar NTO optimization. Despite no OAR objectives being included in the re-optimized plans, these plans had significantly better sparing of the chest wall and lungs.
TBL: In this planning study, a simple, noncoplanar VMAT planning algorithm that optimized dose falloff around the target resulted in significantly better conformity and OAR sparing for lung SBRT plans. | Kei, Pract Radiat Oncol 2025