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Session: Therapy General ePoster Viewing [Return to Session]

Evaluation of the Effects of Energy and Planned Dose Grid On Plan Quality Metrics for Treatment of Single Isocenter Multiple Target Brain Lesions

E Salari, E Parsai*, N Sperling, University of Toledo Medical Center, Toledo, OH


PO-GePV-T-393 (Sunday, 7/10/2022)   [Eastern Time (GMT-4)]

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Purpose: Using a single isocenter for the treatment of multiple brain lesions with Intensity Modulated Radiosurgery (IMRS) has gained acceptance in recent years. One of the challenges of this technique is evaluating plan quality. For Single Isocenter Single Target (SIST) plans, quality metrics such as Paddick Conformity Index (PCI), Paddick Gradient Index (PGI), RTOG Conformity Index (RTOG_CI), and Homogeneity Index (HI) have been used for many years. This study is evaluating the impact of planned grid size (GS) and energy on these metrics for SIMT IMRS plans.

Methods: 10 patients with a total of 40 Volumetric Arc Therapy (VMAT) plans were created and optimized independently in RayStation (V.8A) treatment planning system for the Varian Edge Linac using 6 and 10 Flattening Filter-Free (FFF) beams and GS of 1mm and 2mm resulting in 4 plans per patient. All parameters and objectives except dose grid and energy were kept the same in all plans. Next, PCI, HI, and RTOG_CI for each target, and PGI for each plan were calculated. Then, One-Way ANOVA and two sample T-Test tests were performed for statistical analysis.

Results: Our analysis demonstrates that for PCI, there was no statistically significant correlation to energy for a given GS, but a significant correlation was found with GS, smaller GS yielding higher PCI values (p<0.001). For HI, both Energy and GS were statistically significant classifiers (p<0.05). PGI did not demonstrate any statistically significant differences between groups. For RTOG_CI, GS was a significant classifier (p<0.0001), but the energy was not.

Conclusion: Given the results, we have demonstrated that we may analyze SIMT IMRS plan using existing quality metrics, and for those plans, the expected finer GS and low energy produce statistically significant improvements in those metrics.


Treatment Planning, Treatment Verification, Quality Control


TH- External Beam- Photons: intracranial stereotactic/SBRT

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