Page 64 - Fisica In Medicina n° 1/2017

^Äëíê~Åí=cáëáÅá= =Radiosurgery of brain metastases: comparing Varian EDGE and Gamma Knife Perfexion. A preliminary dosimetric studyS. TOMATIS, P. NAVARRIA, D. FRANCESCHINI, L. COZZI, P. MANCOSU, F. LOBEFALO, G. REGGIORI, A. ASCOLESE, A. STRAVATO, F. ZUCCONI, G. MAGGI, M. SCORSETTIHumanitas Research HospitalPurposeRadiosurgery (SRS) can be delivered with dedicated equipment, like GammaKnife, or with conventional LINAC. Few comparative studies have been conducted. In our institution we designed a phase III randomized trial to evaluate cerebral side effects following SRS delivered by Gamma Knife Perfexion and Linac EDGE. Here some perliminary results on plan dosimetry are presented.Material and methodsPatients with 1 to 4 brain metastases, from any primary except for small cell lung cancer (SCLC) or Lymphoproliferative disease, suitable for SRS were randomized to receive the treatment with GammaKnife or Linac. Planning parameters, including target coverage, paddick conformity index (PCI), gradient index (GI), homogeneity index (HI), maximum and minimum dose to the target were determined. Beam on time (BOT) was also recorded.ResultsFifty patients with 74 metastases (range 1-4) were enrolled in this phase III trial (24 GK, 26 Linac- EDGE). Median prescribed dose was 24 GY (range 20-24 Gy). GTV volume did not show any significant difference in the two arms, PTV was contoured for EDGE only. PCI was better for linac- based plans (0.87 vs 0.69), in contrast, a better GI for gamma knife was observed (2.7 vs 4.2). Due to the specific characteristics of the two delivery systems, HI was lower for linac (0.14 vs 0.49). These results are shown in figure 1. Also BOT was lower for linacs (within 2 min for each target vs about 30-40 min of GK). In our center, linac based immobilization was made by an open mask setup (qfix); CBCT-based IGRT was applied. Patients were monitored by optical surfacemonitoring system (OSMS) during the delivery. Gamma knife immobilization was performed by 55