Dosimetric Uncertainty In Simulation-Free Radiation Therapy: A Comparative Analysis of AP/PA, 3DCRT, and VMAT Planning Techniques for Palliative Spine Patients
Abstract
Purpose
Simulation-free radiation therapy (SFRT) is an emerging paradigm which expedites palliative radiation by omitting a dedicated simulation computed tomography (CT) scan. This study quantifies dosimetric uncertainties associated with SFRT for three different planning techniques.
Methods
Nine previously treated palliative spine cases were retrospectively selected. Each patient had a diagnostic CT (dCT) which was registered to the planning CT (pCT). The PTV and CTV contours were propagated rigidly, and OARs were contoured on both image sets. For each case, anteriorposterior/posterior-anterior (AP/PA), three-dimensional conformal radiotherapy (3DCRT) with three static beams, and volumetric modulated arc therapy (VMAT) plans were generated on the dCT. Using identical monitor units, plans were recalculated on the pCT to estimate the dosimetric uncertainty associated with SFRT workflows. Dosimetric comparison between dCT and pCT plans were performed for CTV V100, lung V20, and spinal cord maximum dose (SCmax).
Results
For AP/PA and 3DCRT techniques, the SCmax difference from dCT and pCT was 44.6 ± 34.8 cGy and 52.4 ± 29.0 cGy, with a maximum discrepancy of 108.2 cGy and 111.4 cGy, respectively. VMAT SCmax difference was 35.5 ± 81.7 cGy, with a maximum discrepancy of -131.4 cGy. CTV V100 differed between dCT and pCT at 0.6% ± 1.0%, -9.3% ± 27.5%, and -34.4% ± 34.3% for AP/PA, 3DCRT, and VMAT, respectively. CTV V100 was below 95% in 78% of the patients for VMAT versus 11% for AP/PA and 22% for 3DCRT. AP/PA, 3DCRT, and VMAT differences in lung V20 were -1.5 ± 1.9 cGy, -2.7 ± 3.6 cGy, and -2.3 ± 4.9 cGy, respectively.
Conclusion
Dosimetric uncertainty associated with SFRT is greater for VMAT when compared to AP/PA and 3DCRT planning techniques. While SFRT planning is clinically warranted for select palliative spine patients, caution should be exercised before omitting the CT simulation when utilizing VMAT treatment planning.