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

Abstract

Purpose The goal of this work was to design a realistic mouse phantom as a useful tool for accurate dosimetry in radiobiology experiments. Methods A subcutaneous tumor‐bearing mouse was scanned in a microCT scanner, its organs manually segmented and contoured. The resulting geometries were converted into a stereolithographic file format (STL) and sent to a multimaterial 3D printer. The phantom was split into two parts to allow for lung excavation and 3D‐printed with an acrylic‐like material and consisted of the main body (mass density ρ=1.18 g/cm3) and bone (ρ=1.20 g/cm3). The excavated lungs were filled with polystyrene (ρ=0.32 g/cm3). Three cavities were excavated to allow the placement of a 1‐mm diameter plastic scintillator dosimeter (PSD) in the brain, the center of the body and a subcutaneous tumor. Additionally, a laser‐cut Gafchromic film can be placed in between the two phantom parts for 2D dosimetric evaluation. The expected differences in dose deposition between mouse tissues and the mouse phantom for a 220‐kVp beam delivered by the small animal radiation research platform (SARRP) were calculated by Monte Carlo (MC). Results MicroCT scans of the phantom showed excellent material uniformity and confirmed the material densities given by the manufacturer. MC dose calculations revealed that the dose measured by tissue‐equivalent dosimeters inserted into the phantom in the brain, abdomen, and subcutaneous tumor would be underestimated by 3–5%, which is deemed to be an acceptable error assuming the proposed 5% accuracy of radiobiological experiments. Conclusions The low‐cost mouse phantom can be easily manufactured and, after a careful dosimetric characterization, may serve as a useful tool for dose verification in a range of radiobiology experiments.

An open source heterogeneous 3D printed mouse phantom utilising a novel bone representative thermoplastic

“…The use of common reference phantoms is an important aspect of the standardized QA approaches needed in pre-clinical laboratories to ensure experiment inter-comparability and repeatability. Previous small animal phantoms have either been geometrically unrepresentative [8], [29], challenging to manufacture and machine to accommodate different detectors [11], [15], [16], internally homogeneous [12], or not tissue equivalent [19].…”

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

“…Both dosimeter types were calibrated to measure dose‐to‐water and so the film layer and polystyrene active element of the PSD were both modeled as water in the corresponding MC simulations. The accuracy of simulating dose to water‐equivalent dosimeters within our phantom relative to the case where the phantom was comprised of tissue‐equivalent material was discussed in our previous work …”

“…Inclusion of heterogeneities boasting a higher mass density and Z eff would therefore allow for phantom measurements which better represent the dose delivered to real mouse tissue, especially in contexts where attenuation in bone is of concern (i.e., intracranial targets), and for lower energy imaging beams where PE interactions become increasingly important. However, we have also demonstrated that replacing the phantom PMMA and polystyrene materials with mouse soft‐tissue, bone, and lung tissue, where appropriate, results in differences of ~5% or less for dose delivered to a water‐equivalent dosimeter at each treatment site . Therefore, considering the agreement between the measured and simulated results presented herein, dose estimates acquired with our current phantom should be sufficiently accurate for estimating dose to mouse soft‐tissue within the suggested accuracy limit (< 5%) for small animal dosimetry.…”

“…An anatomically realistic mouse phantom was 3D printed based on segmented microCT data of a tumor‐bearing 32‐g mouse and is described in detail in our previous work . Briefly, The body was comprised of a transparent, poly(methyl methacrylate) (PMMA)‐like material (ρ = 1.18 g/cm 3 ) that served as an appropriate surrogate for water at the beam energies of interest while the lungs were packed with porous polystyrene (ρ = 0.32 g/cm 3 ) to better represent lung tissue.…”

“…To better allow for preclinical dosimetry verification, it is desirable to have a phantom capable of accommodating dosimeters of the aforementioned variety at target sites of interest. This rational fed back into the design of our group's first‐generation dosimetric mouse phantom, which was designed to accommodate both radiochromic film and a 1‐mm diameter plastic scintillator dosimeter (PSD) . The present work is, therefore, concerned with the dosimetric validation and verification of conformal treatments with the phantom in question using an image‐guided small‐animal irradiator.…”