(Sunday, 7/29/2018) 3:00 PM - 6:00 PM
Room: Exhibit Hall
Purpose: Treatment of multiple metastases with Gamma Knife (GK) might take hours and some patients do not tolerate it. The purpose of this study is to evaluate situations where a combined GK/Linac SRS treatment, in patients with 10 or more brain metastases, is a competitive solution.
Methods: Three treatment plans were performed for each case: a GK plan, a Linac plan, and a combined GK/Linac plan where large lesions (larger than 1 cc) were planned for Linac and the rest for GK. Plans were performed with a prescription dose of 18 Gy and compared in terms of beam-on-time, target coverage and healthy tissue sparing.
Results: Data from three cases has been analyzed. In two of the cases, the large lesions represented 70% of the total volume and were not much larger than 1cc. There was not relevant advantage of using the combined plan approach over GK. However, in the third case: large lesions represented 96% of the total metastases volume. The Gradient Index (GI), V50%/V100%, had the highest value for the Linac plan, followed by the combined plan. The V12Gy had the lowest value in the combined plan. The Conformality Index (CI) calculated as V100% of whole brain/ Volume of total targets, had the lowest value for the Linac plan, followed by the combined plan. The total beam on time (BOT) was 10.5 min, 552 min, and 245.8 min for the Linac, GK and combined plan, respectively. The V12Gy and beam-on-time in case of the Gamma Knife plan was dominated by the largest targets.
Conclusion: This work shows preliminary results on combined GK/Linac treatments. The combined GK/Linac plan resulted in a competitive solution in the case where large irregular lesions represented a significant percent of the total metastasis volume. Future work includes generating and analyzing plans for several more patients.
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