2061 - External Beam Treatment Delivery Efficiency Assessment via Trajectory Log Analysis
Presenter(s)
R. C. Edmondson, S. Shiraishi, D. J. Moseley, and J. Kavanaugh; Department of Radiation Oncology, Mayo Clinic, Rochester, MN
Materials/Methods: Linear accelerator (linac) treatment log files spanning one month were collected from 14 linacs at one institution and its regional clinics. An in-house MATLAB tool was used to read the logs retrospectively and compute dose rate, gantry speed, dose delivered, and maximum instantaneous speed of the multileaf collimators (MLCs). “% constrained” was calculated as the percentage of beam-on time where the gantry speed, dose rate, or MLC speed is greater than 95% of the maximum achievable values for each parameter. Comparisons between c-arm and ring gantries were conducted using a t-test, with matching colors in table showing compared groups. All treatment plans were generated in a single planning system.
Results: Logs for 606 unique VMAT plans of 535 patients were collected, with 115 plans on ring gantry linacs (6 MV FFF @ max 800 MU/min) and 491 plans on c-arm linacs (6 MV @ max 600 MU/min, 6 MV FFF @ max 1400 MU/min, and 10 MV FFF @ max 2400 MU/min).
Ring gantry beam-on time is significantly shorter than c-arm linacs (p<0.01) despite having more arcs. Ring gantry is also significantly more constrained (p<0.01) than c-arm linacs, suggesting potential higher machine usage efficiency.
Gantry and MLC speed are more likely to reach their max limit for highly modulated plans (pancreas). For SBRT plans, dose rate constraint is more often reached, and MLC and gantry speed constraints are less often reached.
Conclusion: Increased delivery efficiency is gained through maximizing multiple delivery parameters, rather than simply increasing the max dose rate. Additional delivery capacity might be achievable through site/technique specific optimizations that maximize multiple delivery parameters.
Abstract 2061 - Table 1
|
| Mean Dose Rate (MU/min) | Beam On Time (min) | # of Arcs | MLC Speed | Gantry Speed | Dose Rate | Total | ||
| % Constrained | |||||||||
| Ring Gantry |
| ||||||||
| Total (n=115) | 494.5 | 2.43 | 3.47 | 61.4 | 62.9 | 34.1 | 158.4 | ||
| SBRT (n=20) | 752.1 | 1.97 | 2.95 | 0 | 0 | 99.0 | 99.0 | ||
| Non-SBRT (n=62) | 438.3 | 2.62 | 3.60 | 74.5 | 76.3 | 19.0
| 169.8 | ||
| Prostate (n=23) | 687.5 | 1.83 | 3.09 | 22.1 | 24.2
| 77.7 | 124.0 | ||
| Pancreas (n=20) | 382.2 | 3.22 | 3.45 | 82.4 | 84.1 | 10.8 | 177.3 | ||
| C Arm |
| ||||||||
| 6 MV (n=300) | 264.4 | 3.49 p<0.01 | 2.99 | 2.2 | 45.5 | 9.7 | 57.4 | ||
| 6 MV FFF (n=101) | 1039.6 | 3.06 p<0.01 | 2.89 | 0.3 | 30.5 | 52.6 | 83.4 | ||
| 10 MV FFF (n=90) | 1183.7 | 3.18 p<0.01 | 2.67 | 1.9 | 46.9 | 28.4 | 77.2 | ||
| SBRT (n=38) | 1084.1 | 3.37 | 2.92 | 0 | 39.5 | 39.7 | 79.2 P<0.01 | ||
| Non-SBRT (n=51) | 426.7 | 3.50 | 2.86 | 2.3 | 42.9 | 14.5 | 59.7 P<0.01 | ||
| Prostate (n=36) | 499.3 | 2.95 | 2.39 | 4.8 | 47.2 | 13.5 | 65.5 P<0.01 | ||
| Pancreas (n=11) | 185.2 | 5.90 | 2.72 | 0 | 51.3 | 5.3 | 56.6 P<0.01 | ||