In-Phantom Film Measurements of Two Treatment Planning Systems for Single-Fraction Spine SBRT
M Taylor1*, J Fontenot2, (1) Louisiana State University, Baton Rouge, LA, (2) Mary Bird Perkins Cancer Center, Baton Rouge, LA
Presentations
(Saturday, 3/26/2022) [Central Time (GMT-5)]
Purpose: To determine whether a significant difference in end-to-end accuracy was present between spine SBRT treatment plans designed by a convolution superposition (CS) based TPS and a Monte-Carlo (MC) based TPS at a number of vertebral sites.
Methods: Single-fraction spine SBRT plans following RTOG-0631 and local institutional guidelines were designed at five vertebral sites in an anthropomorphic phantom using Phillips Pinnacle (TPS-CS) and Elekta Monaco (TPS-MC), which utilize CS and MC dose calculations respectively. A linear accelerator delivered the plans on Gafchromic EBT-XD film inserted transversely at each site. The irradiated films were digitized and registered to the corresponding TPS dose planes. The TPS-calculated and film-measured anterior-posterior (AP) dose profiles through each plan isocenter were plotted and gamma pass rates (GPR) of the dose distribution near the PTV and spinal cord were calculated at various dose difference and distance-to-agreement criteria. For each TPS-film profile pair, the AP dose falloff and profile shift between a common isodose point were measured posterior to the PTV. Each sample was tested for normality with a Shapiro-Wilk test and equality of variances was confirmed between CS and MC samples with Levene's test. An unpaired, equal variance student t-test was then used to test for statistically significant differences between TPS-CS and TPS-MC (n = 5, a = 0.05).
Results: Average GPR across sites were consistently higher in TPS-CS but were only statistically significant in samples with criterion 3%/2mm and stricter. TPS-CS produced more accurate dose falloffs than TPS-MC, while TPS-MC produced smaller isodose shifts than TPS-CS. However, the average differences were each less than a millimeter and not statistically significant.
Conclusion: Within the limits of measurement uncertainty, there was no significant difference in end-to-end accuracy between the spine SBRT plans calculated by each TPS.
Funding Support, Disclosures, and Conflict of Interest: This work was funded by a grant received from Elekta.
ePosters
- 174-60589-16021654-182460-744639702.pdf (M Taylor)
Keywords
Treatment Planning, Stereotactic Radiosurgery, Radiochromic Film
Taxonomy
TH- External Beam- Photons: extracranial stereotactic/SBRT
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