Christie-NPL Heterogeneous Mouse Phantom. Gareth Price, Andrew Robinson, Sean Collins, Giuseppe Schettino, Anna Subiel

Transcription

1 Christie-NPL Heterogeneous Mouse Phantom Gareth Price, Andrew Robinson, Sean Collins, Giuseppe Schettino, Anna Subiel NPL MEMPHYS Workshop on Applications of 3D printing for medical phantoms 29 December 2017 Welcome to the National Physical Laboratory

2 Pre-clinical radiotherapy Transformation in pre-clinical imaging systems in recent years. Better mimic of complex radiation treatments. Cornerstone of radiotherapy/radiobiological research is an accurate knowledge of radiation dose distribution to patient. Rigorous quality standards for clinical radiotherapy Historically, not true for pre-clinical studies. Renewed interest in small animal dosimetry To match advances in pre-clinical radiotherapy delivery

3 Anthropomorphic phantoms Long been used to verify: radiotherapy treatment planning delivery process quality of image guidance systems Christie Anthropomorphic Tomographic Imaging Ellipse (CATIE) Phantom Until recently, phantoms for preclinical research had not developed much beyond the simple cylindrical geometry.

4 Anthropomorphic small animal phantoms Perks et al. (2015) 3D printed a toy mouse replica; machined to accept an IC or MOSFET dosimeter; homogenous; no internal structure. Bache et al. (2015) 3D printed flexible moulds to form radiochromic dosimeters; heterogeneous; relatively simple geometries; used to create a rat section with linear spine region. Welch et al. (2015) heterogeneous mouse phantom constructed rom 2 mm thick slices of TE material milled to anatomical cross-sections; Dosimetry film sandwiched between slices; Constrained geometric realism; Intricate manufacturing process.

5 Tissue equivalent materials/plastics Tissue and bone equivalent plastics developed in the 70 s and 80 s Proportional counter wall material Conducting Thermoplastic filaments have been produced that provide contrast for X-ray imaging e.g. ceramic doped plastics No thermoplastics currently available that provide tissue equivalence

6 Aim Create a pre-clinical phantom of a mouse speed, flexibility, high resolution and low cost of 3D printing anatomically realistic heterogeneous structures from a CT image

7 Fusion Deposition Modelling? We had one available at the time! Different plastics available (PLA, ABS, Nylon, ) More than one material can be printed at the same time. If you have the right machine! Ultimaker 3 Two heads Easy to setup and run We can modify and make the plastic filament ourselves

8 Base thermoplastic: ABS Easy to dissolve with Acetone to add dopant(s) Not the easiest thermoplastic to print Densiyy & photon attenuation characteristics similar to water

9 Dopant: CaTiO 3 CaTiO 3 = 13 % of volume = g cm -3

10 Preparing the Bone TE Plastic* (*IMAGES NOT ALL FROM SAME BATCH/MATERIAL) Impeller mixer (set to max) Drying oven at 40C (~1 week) Weigh out ABS and dopant Mix together in acetone (1 g ABS/5 ml acetone) Ready to print! Extrude a filament granulise

11 Testing the material ICP-MS to confirm the CaTiO 3 ratio MS not a fan of acetone (even trace quantities) 8-10% CaTiO 3 determined (possibly) Bone plastic A block of the material was printed = 1.27 g cm -3 (12 % lower than expected) Result of air gaps? Compared to St. Bart s bone material (epoxy resin)

12 Making the Mouse Model mouse CT image Python toolkit used to segment body, skeleton and lung structures Send to printer Output as STL file format, which can be combined in slicing software

13 Cross-sections of mouse model* (*no lungs in this model)

14 CT Images Overlay of skeletons from mouse (purple) and phantom (grey)

15 Photon attenuation results Mouse Phantom Real Mouse Real mouse Mouse phantom A different mouse used for comparison

16 Going forward Refining the material Improving the photon attenuation at low X-ray energies Check uniformity Repeatability of material production / mouse phantom Calibration certificate Is one required? What needs calibrating? Other equivalent plastics for other tissues 3D printed radioactive hotspots to the mouse phantom Standardised activity

17 NPL 3D Printing Facilities Fusion Deposition Modelling Stereolithography Modelling Filament production

18 The National Physical Laboratory is operated by NPL Management Ltd, a whollyowned company of the Department for Business, Energy and Industrial Strategy BEIS).