Development and Use of Computational Anthropomorphic Phantoms for Medical Dosimetry Nina Petoussi-Henss

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1 Medical Radiation Physics and Diagnostics, AMSD Development and Use of Computational Anthropomorphic Phantoms for Medical Dosimetry Nina Petoussi-Henss HMGU, HELENA Lecture series,

2 Outline Why do we need to know the organ doses of the patient? What are computational anthropomorphic phantoms? Description of various types of anthropomorphic phantoms Estimation of typical patient doses from simulations with the phantoms Dual lattice phantoms for image quality assessment Conclusion remarks 2

3 Mean effective doses per capita and year in Germany (from Bundesamt für Strahlenschutz, 2006) Nuclear medical diagnostics 0.12 msv Radon and daughter nuclides 1.1 msv E = 4.1 msv CT and x-ray diagnostics 1.8 msv 0.4 msv A-bomb tests Chernobyl Nuclear reactors Research Industry <0.05 msv 0.3 msv Food Terrestrial rays 0.3 msv Cosmic rays 3

4 Estimation of organ doses with radiation transport codes (i.e. Monte Carlo codes) Model of the source Model of the body (i.e. phantom) Simulation of: particle interactions energy deposition Appropriate algorithms Simulation results to organ conversion coefficients that have to be multiplied with a measured value 4

5 Computational Phantoms (or Models) Definition - Computerized representation of human anatomy for use in the simulation of the transport of radiation particles from either internal or external sources of radiation Phantom Format Types Stylized (or mathematical) phantoms Voxel (or tomographic) phantoms Hybrid (or NURBS/PM) phantoms Reference represent the average person Patient-specific 5

6 From the mid of 1960s. Still the most widely used 6 From W Bolch, UF

7 From W Bolch, UF From the mid of 1980s Based on medical image data (mostly CT, MRI) 7

8 Voxel Phantoms: The whole body model is made of millions of tiny volume elements (called voxels) Male phantom (Voxel size: mm 3 ) voxels Female phantom (Voxel size: mm 3 ) 8

9 HMGU voxel phantom family (M Zankl, J Becker, U Fill) muenchen.de/amsd/service/scientific- Helga, 26 Donna, 40 Irene, 32 Laura, 43 Klara, 43 Pregnant, 24 week Baby 8 weeks Golem, 38 Frank, 48 Godwin 38 VisHum, 38 Child, 7 Jo, 8 9

10 For legislation standard or reference persons are needed ICRP Reference Computational Phantoms ICRP Publication 110 Ann. ICRP 39 (2), 2009

11 Organ / body contours defined by NURBS or polygon mesh surfaces 11

12 Developed phantom female (preliminary) (Y.S. Yeom, C.H. Kim et al Hanyang University, Seoul, Korea in collaboration with ICRP, HMGU and University of Florida) 12

13 Example: Whole trunk CT examinations with and without tube current modulation Organ dose conversion coefficients per CTDI vol for a whole trunk CT examination (mgy/mgy) Organ w/o TCM Male with TCM w/o TCM Female with TCM Thyroid Colon Stomach Liver Lungs Breast RBM

14 Example for Nuclear Medicine: Organ absorbed doses per unit activity for 123 I (25% thyroid uptake) Absorbed dose per incorporated activity (mgy/mbq) ,1 0,01 0,001 MIRD Frank Reference Man Visible Human Voxelman Donna Helga Irene Golem Bladder Kidn. Sm. Int. Stom. ThyroidAdrenals Colon Liver Lungs E 14

15 Construction of dual lattice voxel phantoms for image simulations Dual lattice means here different voxel resolutions in different parts of the phantom higher resolution in partial body (breast, lung), lower resolution in the rest of the body Breast specimen Lung specimen 15

16 High resolution lung model: Simulation of a thorax examination with EGSnrc

17 Conclusions: Why do we need anthropomorphic phantoms? Organ equivalent dose, the quantity meant to quantify radiation risk is not directly measurable. There is a complex inter-relation between image quality and patient dose. Computational phantoms allow to simulate a variety of exposure conditions The influence of certain measures on patient dose can be studied without actually irradiating a living person. Challenge: how to perform individual, patient-specific dosimetry? Using reference phantoms? Patient-specific? Patient-dependent via the NURBS/PM technique? Using phantom families? 17

18 Acknowledgments Medical Radiation Physics and Diagnostics, AMSD M Zankl, H Schlattl, J Becker, M Greiter, U Oeh, A Zvereva, W Li, C Hoeschen ICRP, International Commission of Radiological Protection W Bolch, University of Florida, US Y S Yeom, C.H. Kim et al Hanyang University, Seoul, Korea Thank you!