RTRB-11MULTIPLE BRAIN METASTASES TREATED WITH SINGLE-ISOCENTER LINAC-BASED STEREOTACTIC RADIOSURGERY (SRS)

Abstract

SRS has been widely employed for treating multiple brain lesions using various techniques with multiple isocenters. A disadvantage of this approach is the prolonged treatment time, which is proportional to the number of lesions. Prolonged treatment time may lead to patient discomfort and movement with attendant risk of undertreating the lesion and increasing dose to normal brain tissue. To shorten treatment time, we and others have moved to a single iso-center approach, which enables parallel irradiation of multiple lesions instead of the conventional serial approach. The aim of this study is to evaluate the clinical results of this treatment approach. Between November-2010 and May-2014 we treated 162 patients with 2 or more lesions (2-5) with a single isocenter SRS approach. Pathologies treated included non-small cell lung cancer, breast cancer, colo-rectal cancer and melanoma, 46%, 22%, 10.7% and 8.7%, respectively. Patients were RPA class I (41.3%), II (26.7%), III (32.0%). Treatment plans were created using ERGO ++ (Elekta, Sweden) planning software or Eclipse™ (Varian, USA) planning software to create inverse intensity-modulated arc therapy (VMAT). Treatments were performed using Synergy-S micro-leaf beam modulator with 4mm leaves, or TruebeamSTx- Novalis with 2.5mm microleaf collimator in the center and 5mm in the periphery. Plans were created using single isocenter with fixed beams, static arcs and/or combination of the both with manual modification of the leave configuration to accommodate the shape and position of the lesions or VMAT plans consistent of 3-4 dynamic arcs. Median survival for RPA I, II, and III was 13.3 months (10.9-17.5), 6.48 months (4.9-8.7) and 4.6 months (3.9-5.5), respectively on Kaplan Meier Survival Analysis. Our initial results suggest that single-isocenter plans can be utilized to deliver conformity equivalent to that of multiple isocenter techniques and efficiently delivered requiring less than half the beam time required for multiple isocenter set ups.