A comparison of robotic radiosurgery (cyberknife) and volumetric modulated arc therapy (VMAT) for small brain metastases

Brain metastases is observed in many primary cancers especially in breast and lung cancer. Brain metastases radiation therapy is applied using small field radiation therapy techniques. The purpose of this project is to make a comparison between treatment plans of SRS (Cyberknife) and volumetric modulated arc therapy (VMAT) of 10 patients of Istanbul University Oncology Institute, who have finished their treatment and comparison of pozitive and negative sides of each method. In this study, 10 patients are chosen, 6 of which have their tumor far from OAR and 4 of which have their tumor close to OAR. The Cyberknife and VMAT plans are prepared by MultiPlan 4.5.3 and Eclipse v16.1 treatment planning systems accordingly. The compared parameters for target volum does are conformity index (CI), gradient index (GI) and homojgeneity index (HI). The doses of organs at risk are compared according to TG101 dose constraints.The parameters in this comparison are recorded from Dose-Volume Histogram (DVH) of the plans. The observed results are analyzed upon the average values. In comparison of the plans prepared by both methods, although the CI and HI are better for VMAT method in patients with tumor far from OAR, GI is better in CK method for the same patients. There is no expressive difference found between the CK and VMAT plans of patients with tumors close to OAR. In comparison of OAR doses, the doses received by OAR are pretty similar in both methods. The 12 Gy isodose volume (V12Gy) which is very important for necrosis is smaller in CK plans of patient with tumors close to OAR according to those of VMAT, however the dose received by 1 cc of normal brain tissue is less in VMAT plans in these patients. No significant difference is observed in doses received by OAR between the two methods. As a result, this study shows that both methods have advantageous parameters, the volumes receiving low dose are better in CK, and MU in CK are much higher than MU of VMAT plans.