Towards patient specific dosimetry in nuclear medicine associating Monte Carlo and 3D voxel based approaches

Transcription

1 Towards patient specific dosimetry in nuclear medicine associating Monte Carlo and 3D voxel based approaches L.Hadid, N. Grandgirard, N. Pierrat, H. Schlattl, M. Zankl, A.Desbrée IRSN, French Institute for radiation protection and nuclear safety, Fontenay-aux-roses, France Institut Curie, Paris, France Helmholtz Zentrum München-German Center for Environmental Health, Neuherberg, Germany International Symposium on Standards, Applications and Quality Assurance in Medical Radiation Dosimetry IAEA, 9-12 November 2010, Vienna

2 Context Results SAF Results Reference doses Results Patient based doses Radiation Protection : Accurate and realistic dosimetry D r T ~ = Ar x r S MIRD Formalism S i n i E i SAF ( r T r S ) Biokinetic aspect Geometric aspect SAF(r r T S) ) = E T /E S M T 2

3 Tabulated reference data SAFs tabulated for mathematical standard geometries Approximations applied for electron SAFs Target region = Source region S=C SAF( C S) = 1 mass source Target region Source region SAF( C S) = 0 C S Walled source regions C S Mathematical phantom SAF( C S) = 2* 1 mass source 3

4 New adult reference computational phantoms of the ICRP Optimisation Monte Carlo calculations Male phantom Female phantom SAFs Photons + Electrons (10 kev<e<10mev) HMGU (EGSnrc) IRSN (MCNPX +OEDIPE) Absorbed doses from radiopharmaceuticals Publication 110 of the ICRP Standard biokinetic of 11 radiopharmaceuticals used in nuclear medicine 4

5 Reference phantoms Fixed geometry 5

6 RESULTS SAF Calculations

7 Comparison between voxelized and ORNL phantoms PHOTONS, SAF (Lungs < Liver), Male Specific Absorbed Fraction (kg -1 ) Low energies Ratio Voxelized/ORNL 25 Different shapes and inter organ distances High energies Ratio Voxelized/ORNL 1,5 Photon energy (MeV) Small influence of the organ shapes on the SAFs 7

8 ELECTRONS, SAF ( Lungs <- Lungs), Male Specific Absorbed Fraction (kg -1 ) Prior approximations SAF( Lungs Lungs) = mlungs=1 kg Ratio 0,99< EGSnrc/MCNPX< 1,01 Low energies : SAF 1 High energies: Electron escape 1 m Lungs Electron energy (MeV) 8

9 Photon SAFs Cross-fire: for many organ pairs, voxel phantom SAFs higher than current values based on mathematical phantoms (inter-organ distances are larger in mathematical phantoms than in reality) Electron SAFs Self-absorption : higher-energetic electrons escape, especially from small organs Cross-fire : SAFs can approach nearly the same order of magnitude as photon SAFs for higher electron energies and organs in close vicinity Application of the ICRP/ICRU reference computational phantoms to internal dosimetry: calculation of specific absorbed fractions of energy for photons and electrons L Hadid, A Desbrée, H Schlattl, D Franck, E Blanchardon and M Zankl Phys.Med.Biol.55 (2010)

10 RESULTS Dose Calculations Mathematical versus computational reference phantoms

11 Reference voxel phantoms Standard biokinetic of radiopharmaceuticals (ICRP 53 + ICRP 80 + ICRP 106) Absorbed doses for 11 radiopharmaceuticals used in nuclear medicine 11

12 0,14 0,12 0,10 0,08 0,06 0,04 0,02 0,00 Context Results SAF Results Reference doses Results Patient based doses Absorbed doses for 18 F-FDG Reference mathematical phantom Reference voxel male phantom Reference voxel female phantom 12 Bladder wall Bones surfaces Brain Breast Stomach wall Small intestine Colon Gall bladder Heart Kidneys Liver Lungs Muscles Oesophagus Ovaries Pancreas Red marrow Skin Spleen Testes Thymus Thyroid Uterus Remaining organs Effective dose Adrenals Absorbed dose per unit activity administered (mgy/mbq)

13 11 C-Methionine Absorbed doses Mathematical versus voxel reference phantoms Differences depend on target organ and radiopharmaceutical 56 % (uterus) 59 % (Urinary bladder wall) 131 I - thyroid uptake 55 % 306 % (lungs) 272 % (lungs) Reasons -Geometric: topology and distances between organs - Physic: approximations previously used for electrons transport 13

14 RESULTS Dose Calculations Mathematical phantoms using OLINDA/EXM versus patient-based phantoms using OEDIPE

15 Creation of the patient based voxel phantoms TPS ISOGray TM Specific voxel phantoms Voxelization Segmentation of 27 organs Attribution of the densities Creation of a voxel phantom : ~ 8 H 15

16 6 female phantoms F1 F2 F3 F4 F5 F6 M1 M2 M3 M4 M5 M6 6 male phantoms 16

17 1,40E 01 1,20E 01 1,00E 01 8,00E 02 6,00E 02 4,00E 02 2,00E 02 0,00E+00 Context Results SAF Results Reference doses Results Patient based doses Absorbed doses for 18 F-FDG for male phantoms M1 M2 M3 M4 M5 M6 Male reference mathematical RCP AM 17 Brain Colon wall Gall bladder wall Heart wall Left kidney Right kidney Liver Left lung Right lung Pancreas Spleen Stomach wall Testis Thyroid Urinary bladder wall Oesophagus Mean absorbed dose per unité activity administered (mgy.mbq 1)

18 Determination of patient based doses : between 9 H and 16 H OEDIPE + MCNPX Maximum absorbed dose differences among patients: factor 3,4 Maximum dose differences between patient based phantoms and Reference mathematical phantoms : ~ 400 % (walled organs) 174 % (brain for 131 I_55%) Reference voxel phantoms : 113 % (thyroid for 131 I_55%) 18

19 + Isodoses curves superimposed on anatomical images DVH Absorbed dose to target organs or tumors 19

20 Thank you for your attention