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Equivalent whole brain dose for patients undergoing gamma knife for multiple lesions
Vikram Jairam, Veronica L. Chang, James Bond and James B. Yu

Introduction: The advent of new radiosurgical technology has enabled the treatment of patients with larger numbers of brain metastases. At what point the whole brain doses delivered in single fraction radiosurgical treatment begin to approximate a fraction of whole brain radiotherapy is unknown. Measuring the equivalent whole-brain dose for multiple lesions may yield useful clinical insights.

Methods: Twelve representative patients were chosen from our institutional database, having undergone radiosurgery for multiple lesions. All patients were treated using the Leksell Gamma Knife Perfexion radiosurgical platform. The entire brain was contoured and mean whole brain dose (MWBD) was calculated. For each plan, all enhancing tumors were outlined and total volume of tumors recorded.

Results: A total of 33 treatments were administered. Three patients underwent radiosurgery a single time, one patient on two occasions, four patients on three occasions, and four patients on four occasions. Median number of lesions treated was 8 (range 1-41). Dose ranged from 18-22 Gy per lesion. The median MWBD per treatment was 1.4 Gy (range 0.2-7.6 Gy). Median total tumor volume was 4.3 cm3 (range 0.048 cm3–21.72 cm3). No patients with less than 25 lesions treated had a MWBD greater than 4 Gy. Total tumor volume was also associated with greater MWBD, albeit with a greater number of outliers.

Conclusion: Both tumor number and volume were associated with increased MWBD. Patients with greater than 25 lesions treated per session or cumulative tumor volumes greater than 10 cm3 had MWBD’s greater than 4 Gy. Furthermore, tumor location and proximity to vital structures are equally important to consider, highlighting the need for individualized treatment planning.

Keywords: Multiple brain metastases, dosimetry, wholebrain radiation therapy, stereotactic radiosurgery, Gamma Knife, tumor volume

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