Exhibit Hall | Forum 4
Purpose: The purpose of this study is to evaluate plan quality for single isocenter single target (SIST) vs. single isocenter multiple targets (SIMT) methods with regards to V12(cc), V8(cc) as well as Paddick conformity (PCI), RTOG conformity (RTOG_CI) and Paddick gradient index (PGI).
Methods: 21 anonymized patient cranial CT scans were used to create treatment plans in RayStation (v10). The number of target was varied between 4-12 per patient. They were different size and distance apart from each other. All targets received the same dose level (24 Gy in 3 fractions) in both plan types. SIMT plans used an isocenter at the midpoint of all targets, with five arcs evenly between 270 and 90 degree couch angles. SIST plans were also made for all targets individually, using five, non-coplanar arcs, designed to minimize exposure to other targets. The SIMT dose distribution was compared to the composite dose of SIST plans by calculating the PCI, RTOG_CI, PGI, V12, and V8 SPSS (v27) was used for two sample T-Test.
Results: A significant difference was observed between two treatment methods for PCI, RTOG_CI. SIMT plans yield better PCI and RTOG_CI compared to SIST, while PGI & V8 were lower for SIST technique. No significant difference was observed between two methods for V12. As the target volumes increased the Paddick and RTOG conformities improved for both techniques. The SIMT treatment plans see much improvement over the SIST as distance between targets decrease and also as the number of targets increase. The mean V12, V8, and GI, however, were better for SIST plans.
Conclusion: Our treatment planning results showed a significant advantage in SIMT plans as the number of targets being treated increases, but if dose gradient and local exposure to critical structures are of concern, then SIST planning should still be considered.
Radiation Therapy, Treatment Planning, Treatment Techniques