32. Comparative study of planimetry for patients with 3 brain metastases treated with Cyberknife: Treatment of 3 lesions separately versus 3 simultaneous lesions

Introduction The aim of this study is to compare the irradiation of three brain lesions treated as consecutive and mono-fractionated to the Cyberknife with simultaneous treatment including the 3 lesions. Methods We study in this work 12 patients with 3 brain lesions who each have been processed at the dose of 20 Gy in 1 fraction. These small tumors (mean 8 cc: min 0.4 cc, max 3.5 cc) were distant from each other. We realized after the fact a planimetry including the three lesions for a simultaneous treatment. To do this, we create a PTV Global volume on which we apply our dose constraints. We then compare the coverage, dosimetric indices (conformity index, homogeneity index, gradient), the processing time and doses to the brain. This study will allow us on the one hand, to assess the feasibility of the treatment, and on the other hand to propose the planimetry to the doctor according to the patient’s case. To improve and secure our study, each patient received a double dosimetry performed by two different operators through the Multiplan planning console, which is dedicated to the Cyberknife. Results The duration of the sessions for the 3 lesions treated simultaneously is acceptable for the patient with values between 45 min and 63 min (mean 55 min), which corresponds to an average increase of 71% (7–127%). This processing time is still acceptable and the simultaneous treatment is time saving for the machine since we have a discrepancy between these two treatment schemes, with an average gain of 83% (59–147%). We evaluated doses received by the healthy brain in the two schemes: V12 Gy, V10 Gy, V8 Gy, V5 Gy. Conclusions In the context of the increase of small brain metastases treatment, the current trend is clearly towards hypo-fractionated treatment of the multi-localizations compared to the treatment of the whole of the brain. The comparison of the two treatment schemes allows us to propose in the future the solution of simultaneous treatment.