Hippocampal Sparing in Stereotactic Radiotherapy for Multiple Brain Metastases: A Comparison of Intensity-modulated Arc Therapy, CyberKnife, and Helical Radiotherapy

OBJECTIVE In this study, we performed a plan study to evaluate brain and hippocampal doses with hippocampal sparing in the treatment of multiple brain metastases with stereotactic radiosurgery (SRS). For this purpose, treatment plans prepared using intensity-modulated arc therapy (IMAT), CyberKnife radio surgery, and helical tomotherapy techniques. The results were compared and evaluated according to their superiority to each other.METHODS Fifteen patients with multiple brain metastases who had a tumor diameter of <3.5 cm were included in this study. IMAT, CK, and HT plans were separately created for each patient. The dose prescription was defined as 18 Gy in the single fraction.RESULTS The D40% of hippocampal (in Gy) averaged 1.63, 1.69, and 0.52 for IMAT, CyberKnife, and Tomotherapy, respectively. The median hippocampal Dmax (in Gy) averaged 2.81, 4.63, and 1.98, respectively. Some plans were statically different in terms of critical organ doses, but the results were clinically acceptable. The mean values of V12 (cc) were found to be 12.6, 38.23, and 37.46 for IMAT, CyberKnife, and Tomotherapy, respectively, when evaluating the doses taken by healthy brain tissue.CONCLUSION Brain radiotherapy is a treatment modality for primary and metastatic lesions. However, after radiotherapy (even with SRS) damage especially in the hippocampus may cause cognitive impairment and a decrease in patients' quality of life. Therefore, when the hippocampus is outlined as organs of risk, it can be protected without compromising PTV coverage. We saw this result in all of three treatment platforms used in this study.