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

Abstract

Purpose/Objective To establish a novel preclinical model for stereotactic radiosurgery with combined mouse-like phantom quality assurance in the setting of brain metastases. Material Methods C57B6 mice underwent intracranial injection of B16-F10 melanoma cells. T1-post contrast MRI was performed on Day 11 after injection. The MRI images were fused with cone beam computed tomography (CBCT) images using the SARRP. Gross tumor volume (GTV) was contoured using the MRI. A single sagittal arc utilizing 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 two mouse-like anthropomorphic phantoms: one in the axial and the other in the sagittal orientation. SARRP output was measured using a PTW Farmer type ionization chamber as per AAPM TG-61 and the H-D curve was generated up to a max dose of 30 Gy. Irradiated films were analyzed based on optical density distribution and H-D curve. Results The tumor volume at 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 Dose max (Dmax) and mean dose were 2048±207 and 1785±14 cGy. Using the mouse-like phantoms, the radiochromic film showed close precision as compared with projected isodose lines with a Dmax of 1903.4 and 1972.7 cGy, the axial and sagittal phantom respectively. Tumor volume 7 days post-treatment was 7.34±8.24 mm3 in the SRS arm and 60.20±40.4 mm3 in the no SRS arm (p=0.009). 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 one death noted. Conclusion Single fraction SRS of 18 Gy delivered in a single arc can be delivered accurately with MRI T1-post contrast based treatment planning. The mouse-like phantom allows for verification of dose delivery and accuracy.

Development of whole brain versus targeted dentate gyrus irradiation model to explain low to moderate doses of exposure effects in mice

“…Conventional facilities, like X-ray cabinets or cesium/cobalt sources, have no onboard CT imaging system allowing brain visualization and do not permit accurate irradiation of such small fields and the localization of millimetric brain structures 21 , 35 . Conversely, the technological properties of SARRP facilities and the parallel recording of MR and CBCT images that favor visualization of structures of interest allowed this high millimetric ballistic specificity 36 – 41 . Until now, experimental studies with the SARRP have been performed to irradiate brain regions at high doses of IR to mimic radiotherapy protocols 38 – 40 , 42 or to inhibit neurogenesis 37 , 43 .…”

Technical Note: Manufacturing of a realistic mouse phantom for dosimetry of radiobiology experiments

“…Welch et al. and Wu et al . accomplished this by using materials that closely mimicked the physical properties of the corresponding anatomy and precise micromachining techniques; unfortunately, the proposed methodology remained laborious and costly.…”

“…More recently, groups have found success creating anatomically accurate mouse phantoms for improved quality assurance in small animal imaging and therapeutic applications. Welch et al 18,19 and Wu et al 20 accomplished this by using materials that closely mimicked the physical properties of the corresponding anatomy and precise micromachining techniques; unfortunately, the proposed methodology remained laborious and costly. Bache et al, 21 on the other hand, used comparatively affordable 3D printed molds, based on rat CT data, to form a homogeneous, tissue-equivalent 3D dosimeter out of radiochromic Presage â material with dose readout accomplished via optical-CT. Zhang et al 22 similarly utilized 3D printing to generate accurate bony and superficial (skin shell) anatomy to enable the construction of a heterogeneous mouse phantom compatible with CT, MRI, and PET imaging.…”

Preclinical dose verification using a 3D printed mouse phantom for radiobiology experiments

“…To date, a variety of anatomically accurate phantoms have been produced for both imaging and radiotherapeutic applications, few of these, however, have had a comprehensive evaluation with respect to their utility as tools for preclinical dosimetry. Welch et al .…”

“…Welch et al . and Wu et al, utilized an anatomically accurate mouse phantom comprised of materials that closely mimicked the physical properties of the component anatomy; however, their phantom was fabricated using less‐economical micromachining techniques which did not preserve the outer contours of the mouse model. Bache et al, in contrast, used comparatively affordable 3D printed molds, based on rat CT data, to form a homogeneous, tissue‐equivalent 3D dosimeter out of radiochromic Presage ® material with dose readout accomplished via optical‐CT.…”