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

Int J Radiat Oncol Biol Phys. 2017 Sep 1;99(1):191-201. doi: 10.1016/j.ijrobp.2017.05.016. Epub 2017 May 19.

Abstract

Purpose: To establish a novel preclinical model for stereotactic radiosurgery (SRS) with combined mouselike phantom quality assurance in the setting of brain metastases.

Methods and materials: 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 × 3 mm2 collimator was used to deliver 18 Gy prescribed to the isocenter. MRI was performed 7 days 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 PTW Farmer 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 30 Gy. Irradiated films were analyzed based on optical density distribution and H-D curve.

Results: The tumor volume on day 11, before intervention, was 2.48 ± 1.37 mm3 in the no-SRS arm versus 3.75 ± 1.19 mm3 in the SRS arm (NS). In the SRS arm, GTV maximum dose (Dmax) and mean dose were 2048 ± 207 and 1785 ± 14 cGy. Using the mouselike phantoms, the radiochromic film showed close precision in comparison with projected isodose lines, with a Dmax of 1903.4 and 1972.7 cGy, the axial and sagittal phantoms, respectively. Tumor volume 7 days after treatment was 7.34 ± 8.24 mm3 in the SRS arm and 60.20 ± 40.4 mm3 in the no-SRS arm (P=.009). No mice in the control group survived more than 22 days after implantation, with a median overall survival (mOS) of 19 days; mOS was not reached in the SRS group, with 1 death noted.

Conclusions: Single-fraction SRS of 18 Gy 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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Brain Neoplasms / diagnostic imaging
  • Brain Neoplasms / pathology
  • Brain Neoplasms / radiotherapy*
  • Brain Neoplasms / secondary
  • Cone-Beam Computed Tomography
  • Contrast Media
  • Magnetic Resonance Imaging
  • Male
  • Melanoma / diagnostic imaging
  • Melanoma / pathology
  • Melanoma / radiotherapy*
  • Melanoma / secondary
  • Mice
  • Mice, Inbred C57BL
  • Multimodal Imaging / methods
  • Phantoms, Imaging*
  • Quality Assurance, Health Care*
  • Radiosurgery / standards*
  • Radiotherapy Dosage
  • Time Factors
  • Tumor Burden

Substances

  • Contrast Media