Comparison of two different treatment systems in multiple brain metastases plans

Stereotactic radiosurgery (SRC) is used for the treatment of small diameters tumors. CyberKnife (CK) and Linear accelerators (Linac) are treatment systems which are widely used in management of solitary brain and mutliple brain metastases using SRC. The purpose of this study is to compare the CK and Linac treatment plans in patients with multiple brain metastasis. We used single fraction and similar target coverage to identify the differences between CK and Linac based treatment plans. In this study, the number of brain metastasis differed between 3 to 8 in total number of 17 patients. In this study, the maximum critical organ doses and dose volume parameters were investigated for optical nerve, chiasm, cochlea, brainstem. We compared the volume of normal brain tissue which received 8, 10, 12 Gy dose levels and MU values. In this study, Linac plans were made using volumetric modulated arc treatment (VMAT) technique by using 6 MV, 6 FFF, 10 FFF energies. We have made either 3 or 4 arc VMAT plans for each energy and reached total number of 6 plans. Maximum critical organ doses, volume of normal brain tissue which received 8, 10 and 12 Gy dose levels, CI, GI, HI and MU were investigated in each plan. Different plans were compared by using statistical tests. However, we colud not find any significant diffenerce between 6 plans. We tried to find the best plan by scoring best results for each plan. Best plan was seleceted for each patient. We identifed 6 FFF plans as the best plan for 3 to 4 brain metastasis. If patients have more than 4 lesions, 6 MV and 6 FFF are comparable. We could not find any superiority of 10 FFF plans for all patients. We could not find any difference between for different number of arcs used. The best Linac plans were selected and compared with CK plans. Comparison between CK and Linac plans were significantly different in terms of critical organ doses however they found to be clinically acceptable. Normal brain tissue parameters like V8 (%), V8 (cc), V10 (%), V10 (cc), V12 (%) and V12 (cc) were found to be supeiror for Linac plans compared to CK (p <0,05). MU values, which shows the treatment time also found to be better for Linac plans (p<0,05). In terms of normal brain tissue dose parameters and MU values, Linac plans found to be superior compared to CK plans. The results of this study have shown a better profile for Linac plans. CK and Linacsare used in management of brain metastasis by using SRC. The findings of this study is relevant for the patients seleceted for this study and results indicated the superior findings for Linac plans compared to CK plans.