Room: Davidson Ballroom A
Purpose: To evaluate stereotactic radiosurgery (SRS) plans using a Linac non-conformal arc-based (HyperArc(TM)) platform with either standard 5mm multi-leaf collimator (MLC) or 2.5mm micro-MLC versus those using Gamma Knife (GK), the "gold standard."
Methods: Thirteen previously treated GK patients (16 total lesions were anonymized and sent to Eclipse TPS (version 15.5) for planning using the HyperArc(TM) module. These included eight with benign skull base tumors (meningiomas, acoustic neuromas and pituitary adenomas), four brain metastatses cases and one with post-metastectomy cavity. Each patient was re-planned using a standard TrueBeam (TB) linac with 5mm MLC and a 2.5mm micro-MLC linac (Edge). All plans were compared against each other using the following measures: Gradient index (GI), Paddick conformity index (CI(Paddick)), RTOG conformity index (CI(RTOG)), and both target and organ-at-risk (OAR, including brainstem, optic chiasm and optic nerves) mean and maximum doses.
Results: All plans were considered clinically acceptable. CI was better for the Linac based plans, with Edge plans tending to be closer to ideal. Edge plans had better coverage with similar or slightly lower OAR dosages, though the advantage of micro-MLC leaves became less obvious for targets greater than approximately 1.3cc. Exceptions to this were lesions in close proximity to OARs. GI was better for GK in all but one Linac based-plan, and significantly better for approximately 60% of the lesions. There seemed to be no pattern to the types of target that showed better GI, so possibly with more time in planning, this difference could disappear, especially for Edge HyperArc(TM) plans.
Conclusion: HyperArc(TM) plans created for a standard Linac with 5mm MLC leaves are comparable to the Gamma Knife plans in all cases, with those planned for 2.5mm micro-MLC Linacs showing superiority for very small lesions and lesions in close proximity to OARs.
Funding Support, Disclosures, and Conflict of Interest: HyperArc(TM) software used in this work was provided by Varian Medical Systems