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Clinical Implications of Stereotactic Treatments On Cross-Vendor Linear Accelerators Equipped with Two Different Image-Guided Systems

J Hill*, B Ruiz , Johnson City Medical Center, Johnson City, TN


(Sunday, 7/14/2019)  

Room: ePoster Forums

Purpose: To compare the clinical implications of delivering stereotactic radiosurgery (SRS) treatments on cross-vendor linacs planned with different techniques and monitored with two, different image-guided systems.

Methods: 16 patients of similar prescription, number of targets and their volumes were planned — 8 in Brainlab Multiple Mets (DCA technique) and 8 in Varian Eclipse (VMAT technique). Treatments were delivered on a Varian Truebeam with Optical Surface Monitoring (OSMS) and on an Elekta VersaHD with Brainlab Exactrac (ETX) and localization performed via CBCT and ETX respectively. Dosimetric comparisons were made in-terms of Paddick conformity index (CI), under/over treatment ratios (UTR, OTR), and gradient index (GI). To determine the practical differences in treatment delivery, average setup and delivery times and intrafractional shifts were also compared.

Results: Total patient throughput time, setup time, and delivery time was 23.76±6.67min, 8.46±6.35min, and 15.31±2.66min for VersaHD/ETX respectively, and 13.22±5.66min, 8.66±5.02min and 4.56±1.61min, respectively for Truebeam/OSMS. Intrafraction monitoring showed magnitude error of 1.1±0.4mm and 0.55±0.25mm for ETX and OSMS respectively. Maximum rotational error about any one axis was 3.5° and 0.7° respectively for ETX and OSMS. CI, UTR, and OTR were 0.725±0.045, 0.998±0.002, and 0.727±0.044 for DCA plans respectively, and 0.888±0.027, 0.965±0.02 and 0.921±0.033 respectively for VMAT. GI was 3.73±0.65 and 4.44±0.82 for DCA and VMAT respectively.

Conclusion: With similar setup times, delivery times were a function of the configuration used. OSMS monitoring is continuous and showed intrafractional motion below tolerances during all fractions, never prompting x-ray re-verification — in contrast to ETX. Dosimetric indices show that the DCA technique provides virtually no under-treatment of target volumes, while VMAT provides less instances of over-treatment, demonstrating a slight advantage in prescription coverage with DCA. A statistically significant improvement in GI was indicated with DCA treatment plans. Trade-offs in treatment delivery and dosimetric plan quality were apparent in this study.


Not Applicable / None Entered.


TH- External beam- photons: intracranial stereotactic/SBRT

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