Program Information
Implementation of the Conformity/Gradient Index (CGI) to Intracranial, Linac-Based Stereotactic Plans to Evaluate Possible Improvements in Treatment Planning
A Sandu1*, S Thompson2 , A Ayan3 , J Woollard4 , N Gupta5 , (1) Ohio State University Columbus, OH, (2) Varian Medical Systems, Palo Alto, CA, (3) Ohio State University Columbus, OH, (4) Ohio State University Columbus, OH, (5) Ohio State University Columbus, OH
Presentations
SU-F-T-605 (Sunday, July 31, 2016) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose:To retrospectively evaluate the planning quality of a sample of intracranial, linac-based, dynamic arc MLC and VMAT stereotactic plans by calculating the effective gradient, Conformity Score (CGIc) and Gradient Score Index (CGIg), and determine if the Conformity/Gradient Index (CGI) may be a useful metric to guide our current treatment planning process.
Methods:We evaluated single lesion VMAT, single lesion dynamic arc, and single isocenter, 2-lesion linac-based, intracranial, VMAT treatment plans originally created in Eclipse™. The CGI index was calculated for each lesion using the Target Volume (TV), the Prescription Isodose Volume (PIV), and the 50% Isodose Volume. The effective gradient was obtained directly from the Eclipse “gradient measure.”
Results:From the single lesion cases, target volumes of ≤ ~2cc reliably achieved an effective gradient of ~3mm and a CGI > 95. For lesions ≤ ~20cc, the majority of cases have an effective gradient of <5mm and a CGI > 90-95. For our multi-lesion data, we determined that lesions separated by <2cm typically had CGI values of 75-85, lesions separated by 2cm-3cm typically had CGI values > 80-85, and lesions separated by >3cm can have CGI over 90.
Conclusion:The CGI metric is a simple tool that can be applied to MLC-based stereotactic planning, requires only three pieces of data, and quickly allows planners to evaluate and determine if a plan is suboptimal. Our data identified several cases that might be improved with additional effort and/or re-planning, but the majority of the treatment plans evaluated fell within a desirable CGI range. Cases deemed suboptimal are currently under investigation and will be re-planned to determine if CGI values can be improved.
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