Quality Assessment of Stereotactic Radiosurgery of a Melanoma Brain Metastases Model Using a Mouselike Phantom and the Small Animal Radiation Research Platform

Abstract

To establish a novel preclinical model for stereotactic radiosurgery (SRS) with combined mouselike phantom quality assurance in the setting of brain metastases. C57B6 mice underwent intracranial injection of B16-F10 melanoma cells. T1-weighted postcontrast magnetic resonance imaging (MRI) was performed on day 11 after injection. The MRI images were fused with cone beam computed tomography (CBCT) images using the Small Animal Radiation Research Platform (SARRP). The gross tumor volume (GTV) was contoured using the MRI. A single sagittal arc using the 3×3mm2 collimator was used to deliver 18Gy prescribed to the isocenter. MRI was performed 7days after radiation treatment, and the dose delivered to the mice was confirmed using 2 mouselike anthropomorphic phantoms: 1 in the axial orientation and the other in the sagittal orientation. The SARRP output was measured using a PTWFarmer type ionization chamber as per the American Association of Physicists in Medicine Task Group report 61, and the H-D curve was generated up to a maximum dose of 30Gy. Irradiated films were analyzed based on optical density distribution and H-D curve. The tumor volume on day 11, before intervention, was 2.48±1.37mm3 in the no-SRS arm versus 3.75±1.19mm3 in the SRS arm (NS). In the SRS arm, GTV maximum dose (Dmax) and mean dose were 2048±207 and 1785±14cGy. Using the mouselike phantoms, the radiochromic film showed close precision in comparison with projected isodose lines, with a Dmax of 1903.4 and 1972.7cGy, the axial and sagittal phantoms, respectively. Tumor volume 7days after treatment was 7.34±8.24mm3 in the SRS arm and 60.20±40.4mm3 in the no-SRS arm (P=.009). No mice in the control group survived more than 22days after implantation, with a median overall survival (mOS) of 19days; mOS was not reached in the SRS group, with 1 death noted. Single-fraction SRS of 18Gy delivered in a single arc can be delivered accurately with MRI T1-weighted postcontrast-based treatment planning. The mouse like phantom allows for verification of dose delivery and accuracy.