Design and Fabrication of Kidney Phantoms for Internal Radiation Dosimetry Using 3D Printing Technology

Transcription

1 Design and Fabrication of Kidney Phantoms for Internal Radiation Dosimetry Using 3D Printing Technology Johannes Tran-Gia, PhD NPL MEMPHYS Workshop Applications of 3D Printing for Medical Phantoms Klinik und Poliklinik für Nuklearmedizin Direktor: Prof. Dr. Andreas Buck

2 Radionuclide Therapy Patient Radiopharmaceutical Uptake Aim: Destruction of malignant tissue (e.g. tumor) Risk: Toxicity in healthy organs (e.g. kidney / bladder) Dosimetry in nuclear medicine: Determine dose to organs-at-risk 2

3 Uptake U S [%] Simple Dosimetry Source organ S Measured activity in source organ S TIAC S = U S t dt TIAC S [1] ( residence time ): # decays in source organ S Time after injection t [h] Dose to target organ T: D T = A 0 TIAC S S T, S [1] Time-Integrated Activity Coefficient. S Dose factors 3

4 Quantitative SPECT/CT Imaging SPECT/CT acquisition Reconstruction Counts per Voxel Activity per voxel Dose distribution Conversion factor (cps/mbq) Counts Activity 4

5 Partial Volume Effect Source: Wikipedia Partial volume effect ( spill-out vs. spill-in ) Simulation PSF (Gaussian) SPECT CT Resolution Image Formation: Convolution of true object with point spread function (PSF) of the imaging system ( How does the imaging system see the object ) 5

6 Partial Volume Effect Source: Wikipedia Partial volume effect ( spill out vs. spill-in ) SPECT CT Simulation CT-based VOI = Object: Underestimation of counts due to spill out VOI > Object: Inclusion of counts lost due to spill out (simple partial volume correction) 6

7 Partial Volume Correction 1: Recovery Coefficients Question: Ratio of counts lost due to spill out in examined organ Approach: Correction by recovery coefficients (RC) Determination of RC in spheres of different volumes (V) RC-V curve RC-V curve RC= Activity inside VOI Total activity CT-based VOI SPECT reconstruction biodex.com Sphere inserts SPECT/CT acquisition with VOI 7

8 Partial Volume Correction 1: Recovery Coefficients Application of RC: Activity quantification in CTbased VOI RC RC-V curve Determination of RC(V) from correction curve Correction of spill out Problem: V 177 Lu-PSMA SPECT/CT kidney VOI RC-V curve determined based on spherical geometry Potential error for more complex geometries Activity= Activity inside VOI RC V 8

9 Partial Volume Correction 2: 3D Printed Phantoms [1] Idea: Replacement of spheres with more realistic geometries (e.g. kidney) Sphere inserts biodex.com turbosquid.com Kidney geometry Realisation: 3dprint.com conrad.de CAD design [2] thingiverse.com Fabrication with low-cost 3D printer Kidney models 3D printer [1] Tran-Gia et al., JNM (2016). [2] Computed-Aided Design. 9

10 CAD Modeling of Kidney Phantoms Software: Autodesk Inventor 2016 Professional CAD [1] design of kidneys & reference spheres of equal volumes for 4 different age groups based on MIRD 19 [2] Kidney Sphere Kidney Sphere Filling Attachment Newborn ~ 9 ml 1 year ~ 24 ml Kidney Sphere Kidney 1.2 mm Sphere 5 years ~ 44 ml Adult ~ 123 ml [1] Compuder-Aided Design [2] Bouchet et al., J Nucl Med 2003;44:

11 Slicing of the CAD Models for 3D Printing Printer control: Repetier-Host (v1.5.0) [1] Embedded slicing software: Slic3r (v1.2.9) [2] Support material Adult kidney Corresponding reference sphere [1] [2] 11

12 3D Printing Printer: Renkforce RF1000 (FDM) Filament: Voltivo ExcelFil PLA (3 mm, transparent) Extruder Movable printing plate Support material Close-up view 3D printing from above Finished object Printing parameters: layer thickness: 0.2 mm, v max : 60 mm/s, temperatures: 63 C (plate), 227 C (extruder), Ø Extruder = 0.5 mm 12

13 Refinement of the Phantom Inserts Removal of support material Hole for filling Holes for filling (M1.2) Agglutination of individual parts (two-component adhesive) Coating with epoxy resin (watertightness & chemical stability) Thread profiles for attachment in the body phantom Closure: Plastic screw & O-ring Support Printed renal cortex with support Screw & O-ring Threads Refined kidney phantoms 13

14 SPECT/CT Acquisition: Setup & Reconstruction Recon of adult kidney (Lu-177) IEC NEMA phantom Drawn Volumesof-Interest Recon of adult sphere (I-131) Sphere insert SPECT/CT acquisition 14

15 More Realistic Kidney Model (2 Compartments) Kidney dimensions: Sonography study (665 volunteers) [1] Length [mm] Width [mm] Depth [mm] V kidney [cm 3 ] V Cortex [cm 3 ] V Medulla [cm 3 ] Female Male Division according to ICRP 89 [2] [3] Cortex: 70% of kidney volume Medulla & collecting system: 30% Aim: Simulate the non-uniform, arch-shaped activity distribution typically observed in 177 Lu-DOTA therapies by filling only the cortical compartment [3]. [1] Emamian et al. AJR (1993). [2] ICRP 89. [3] MIRD Pamphlet

16 CAD Model & 3D-Printed Parts Medulla Cortex Filling Cortex Filling Medulla CAD model 1. CAD modelling Separate pieces after 3D printing 3. 3D printing 2. Printer control & Slicing 4. Finalization (holes, threads, etc.) 16

17 Cross-Section & SPECT/CT Acquisition Cross-section SPECT/CT acquisition ( 177 Lu, xspect Quant, 48i, 1s, no filtering) Cortex (70%) Medulla (30%) Possibility to investigate partial volume effects and corrections! More at EANM 2017! 17

18 Influence of Post-Reconstruction Filtering SPECT reconstruction Cross-section Kidney phantom, hot cortex Sphere phantom, homogeneously filled Appearance of unfiltered torus similar to filtered sphere Problem in patients! SPECT/CT acquisition: 177 Lu, xspect Quant reconstruction 18

19 Next Step: 3D Printing of Patient-Specific Kidneys 177 Lu-PSMA therapy 3D-Printed 2-Compartment Kidney Organ-at-risk Extract kidney from CT Investigate partial volume errors Improve accuracy of quantitative SPECT BUT: Delineation between hot and cold parts of the organ-of-interest can be challenging! 19

20 Summary Quantitative SPECT/CT imaging: 3D activity distribution in patients ( important for dosimetry) Major problem: Quantification errors caused by partial volume errors 3D printing: Organ-specific phantoms Patient-specific correction of partial volume errors 3D-printed kidney 177 Lu-PSMA 20

21 Thank you very much for your kind attention!