Dosimetric Evaluation of the Treatment Goals Effectiveness of VMAT / Cyber Knife Versus IMPT When LET / Variable RBE Are Taken Into Consideration for Brain Tumors
Presentations
PO-GePV-M-297 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
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Purpose: Provide a dosimetric comparative study of the VMAT / CK brain plans versus IMPT treatment plans of brain tumor patients while taking the LET and variable RBE into considerations.
Methods: A novel commercial Monte Carlo based dose computation with the ability to compute the dose average LET ( RayStationIonPG Research9) with variable RBE modeling was used in this study. The MC dose engine tool was validated against measurements of our IMPT system (IBA, Proteus Plus). A cohort of 5 brain tumor patients with variable target size and locations were selected randomly for this study. Three treatment plans were generated retrospectively for each patient, where VMAT, CK, and IMPT systems were used for planning. Inverse optimization was used following our standard clinical procedures with standard dose constraints for OARs. For the IMPT plans, the LET calculations and various RBE models were computed following the inverse planning. The DVH dosimetric quantities of the three planning techniques were used as a metric of the plan performance for each technique. In case of IMPT DVH values were generated using two RBE models (Carabe & McNemara' s models).
Results: For the five patients, the generated plans of each modality performed equivalently in terms of the target coverage D98 and D95. The OAR dose was in average lower for the IMPT, CK, and VMAT in order. Dmax for several critical structures was used as a metric in this study and showed that 2 out of 5 patients had higher Dmax by average of 4% to optical structures compared to CK. For the rest of the cases there OAR dose showed dependency on the anatomy and location of the tumor
Conclusion: When taking the proton variable RBE effect into account, the IMPT and CK showed a better OAR sparing compared to VMAT for brain tumor patients.
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