A dedicated tool for PET scanner simulations using FLUKA

Transcription

1 A dedicated tool for PET scanner simulations using FLUKA P. G. Ortega FLUKA meeting June

2 Need for in-vivo treatment monitoring Particles: The good thing is that they stop... Tumour Normal tissue/organ at risk Wanted: In-vivo range verification In-vivo dosimetric verification Desirable: A procedure for the verification of the irradiation field position of the particle range simultaneous with the therapeutic irradiation and, in particular, a procedure for the quantification of the dose distribution in-situ, in-vivo and in real time. the bad thing is that we have to know where! 2

3 Need for in-vivo treatment monitoring Check for: Mispositioning Anatomical changes Patient & organ movement Treatment mistakes and accidents We need a way to obtain real-time information about the treatment by analyzing the secondary radiation exiting the patient Among the possible monitoring methods, Positron emission tomography (PET) is currently the only available technique for non-invasive monitoring of ion beam dose delivery, tested in several clinical pilot studies. 3

4 PET treatment monitoring Positron Emission Tomography (PET): Detection of induced β + -activity formed as by-product of irradiation with ion beams Careful! AA(rr) DD(rr) : Non trivial relation Measured activity compared with MC calculation From K. Parodi 4

5 Also possible for other ions C ions (212 MeV/n) Protons (110 MeV) 11C, 10C 15O, 14O 11C, 13N,... K. Parodi et al, IEEE TNS 2005 Projectile + target β+-activation Only target β+-activation By-product of irradiation (15O, 11C, 13N...with T1/2 ~ 2, 20 and 10 min) 5

6 Calculation model of β+ activation FLUKA Monte Carlo code describes β+ emitter distribution for CT-based calculations in patient using Planning CT (segmented into 27 material) and same CT-range calibration curve as TPS (Parodi et al MP 34, 2007, PMB 52, 2007) Experimental cross-sections for β+ emitter production Semi-empirical biological modeling (Parodi et al IJROBP 2007) Convolution with 3D Gaussian kernel (7-7.5 mm FWHM) 6

7 FLUKA code development for (p,d), (n,d) reactions Excitation functions 12 C(p,x) 11 C and 16 O(p,x) 15 O, relevant for PET : Now deuteron formation at low energies is treated directly and no longer through coalescence (Data: CSISRS, NNDC, blue Fluka2011.2, red Fluka2013.0) 7

8 Flair tools for medical applications Flair is the GUI for FLUKA It helps with the creation of the input, provides a Geometry Editor to visualize and modify the geometry, allows to run, compile user routines, process the output files... and includes tools for medical applications like DICOM to FLUKA voxel geometry conversor and PET geometry builder 8

9 DICOM to FLUKA voxel geometry tool Imports DICOM files and translate them into FLUKA voxels. the folder containing all the DICOM files should be introduced. Flair will read it through and show the information for each slice (complete header) Just select the slice you are interested in and hit the voxel tab! 9

10 DICOM to FLUKA voxel geometry tool Imports DICOM files and translate them into FLUKA voxels. It is necessary to provide a file with the material definition list and another file with the assignment of materials for each Hounsfield Unit. Usually different materials for HU divided in intervals from 1050 HHHH 3100 Association of given HU interval with material and additional density and stopping power correction factors (Editable!) Process DICOM files and generate VOXEL and scoring mesh 10

11 Flair tools for PET simulations Provided the basic parameters for the PET scanner the tool generates the geometry, thanks to the lattice capabilities of FLUKA. Two sections: - Definition of the module (array of scintillator crystals): number of crystals, dimensions, spatial separation. - Definition of the ring: Number of modules, radius, opening angle (for full or partial rings), scintillator material. 11

12 Flair tools for PET simulations Several templates from commercially available PET scanners are included in the tool The user is free to edit the parameters for his particular situation before including it in the final geometry. 12

13 Flair tools for PET simulations 13

14 Flair tools for PET simulations Taking advantage of DICOM to FLUKA voxel geometry tool Optimized geometry of the simulation ready in few steps! All the elements can be easily adapted to each situation. 14

15 Flair tools for PET simulations Dedicated scoring, prepared to store the data in Interfile 3.3 binary format, list mode or particle track information Ready to use with external reconstruction algorithms Possibility to choose scoring parameters: o Arc correction. The radial bin size is corrected for the circular shape of the detector. o Maximum Ring Difference (MRD). The difference between two rings events can be restricted to a maximum value. o Span. Extent of axial data combined. Reduces the size of the stored data. o Mashing factor. Reduction of the angular sampling. Reduces the size of the stored data. o Number of segments. Parameter related to MRD and span number. Defines the number of segments the cells in the Michelogram can be divided. 15

16 Simple proof-of-concept of dedicated tool Measurement of two NEMA-like phantoms as a proof-of-concept, using an Ecat EXACT HR+ scanner with the standard scoring settings: The black cylinders have 4 times more activity than the background (gray). White areas are cold. 16

17 Simple proof-of-concept of dedicated tool 10 9 isotopes simulated and reconstructed with STIR filtered back-projection 3D reprojection (FBP3DRP) algorithm, simple but enough for our purposes. Original phantom Big phantom Small phantom section reconstruction reconstruction Scoring parameters: Span=9, MRD=22, No mashing factor, with 5 segments Some artifacts are present, due to simple reconstruction algorithm, but good overall description of the phantom. 17

18 Conclusions Recent FLUKA code developments improve the description of deuteron formation in reactions important for PETrelated studies, like the generation and distribution of β+ emitters for hadron-therapy. A dedicated tool for DICOM to FLUKA voxel geometry conversor and a tool for PET scanner geometry building have been presented, integrated into Flair, the GUI for FLUKA. The use of these tools allows a complete simulation of clinical studies and PET monitoring in few steps. Image from K. Parodi et al. IJRBOP

19 Thanks for your attention! Work partially founded by: 19