Dosimetry in Nuclear Medicine – Importance and necessity


Organizers and Instructors:

Michael Ljungberg is working with teaching and research with Monte Carlo simulation of scintillation camera imaging and SPECT, attenuation and scatter correction for dosimetry.

Bo-Anders Jönsson is programme coordinator for the medial physics education at University of Lund. Research field is internal dosimetry with focus on small scale dosimetry.

Michael Stabin teaches and performs research in the area of model development for internal dose assessment, performs dose calculations for new and existing radiopharmaceuticals, and uses Monte Carlo simulation methods in dose assessment and detector development.

Sven-Erik Strand has been working with nuclear medicine physics in the field of scintillation camera performance, beta camera and internal dosimetry. He has been part of many clinical applications where his main interest is now in radionuclide therapy. He is full professor with teaching of medical physicists.

Course length
1 day

Title of course
Dosimetry in Nuclear Medicine – Importance and necessity

Course Description
By dosimetry, we mean calculation of the energy imparted by radiation per unit mass and the relation of this parameter to biological effects, such as the risk of cancer induction or cell death. The MIRD methodology, developed to standardize radiation dose calculations in nuclear medicine, is based on a stylized computer phantom representing a reference man (or woman). The absorbed doses per unit activity from source organs to target organs are then calculated. For patient specific dosimetry in radionuclide therapy, however, different approaches need to be considered that include the patient-specific geometry and biokinetics. Here, nuclear medicine imaging with proper correction for photon attenuation, scatter and collimator resolution is needed to obtain as the most accurate activity maps as possible. Multiple studies are required to investigate the activity distribution over time. The absorbed dose to surrounding tissue, tumor and critical organ are calculated, using MIRD S-values, directly from activity imaging using convolution methods, or by direct Monte Carlo calculation. A registered anatomical image is required for the dose calculation. The absorbed dose depends on the radionuclide and on biological half-life and special care should be considered for radiation-sensitive organs, such as the bone-marrow.

This course is designed to give an overview of the evolving dosimetry field in nuclear medicine and look into the different technologies as Monte Carlo, SPECT, PET dosimeters, high resolution imaging and so on necessary for developing dosimetry methods with high accuracy. The course includes lectures on types of radiation and their relative biological effects, how to measure activity distributions in vivo and the inherent limitations of such measurements, how to go from activity to absorbed dose, and how dosimetry models can be useful when going from macrodosimetry base on scintillation camera images to small scale dosimetry at the tissue and cellular level.

Course outline

I. The absorbed dose concept in diagnostic and therapeutic nuclear medicine.

A. Historical background
B. Internal and external dosimetry
C. Radiation source
D. Dosimetry for diagnostic nuclear medicine
E. Dosimetry for therapeutic nuclear medicine
F. Dosimeters for nuclear medicine
G. Implementations in the clinic

II. Radionuclides useful for Diagnosis and Treatment in Radionuclide Therapy

A. Radionuclide for therapy
B. Photon emitters
C. Electron emitters
D. Auger-electrons
E. Alpha-particles
F. Imaging problems with RNT nuclides

III. The MIRD dosimetry model and its limitations for Patient-Specific Radionuclide Therapy

A. Internal dose concepts
B. MIRD system
C. Kinetic models and study design
D. Human body and organ models
E. Resources for dose calculations

i. Literature resources
ii. Software tools
F. Practical examples

G. Recent experiences with the drug approval process

IV. Activity Calculations from Planar and SPECT Activity Images

A. Planar method -Geometrical-Mean
B. Reconstruction methods
C. Scatter and attenuation correction
D. Collimator penetration and its effect on image quality
E. High Count-rate problems

V. The small intestine as an example of a dosimetry model

A. The ICRP 30 GI tract model
B. Cylinder model
C. Cross-doses and wall activity model
D. Sestamibi as an example

VI. The importance of bone-marrow dosimetry

A. Marrow as a radiosensitive tissue
B. Calculating the time-activity integral in the marrow
C. Marrow dose conversion factors
D. Assignment of patient-specific marrow dosimetry
E. Correlating dose with effects

VII. Aspects going from large to small scale dosimetry

A. Biological considerations and pitfalls with internal dosimetry
B. Spatial distribution of radioactivity
C. Implications of non-uniformity for dose distribution
D. Techniques and procedures
 

VIII. The future role of Monte Carlo simulations in dosimetry

A. Development of voxel-based body and organ phantoms
B. Patient-specific dosimetry based on patient images
C. Marrow dose models from MR images
 

IX. Summary

A. International Dosimetry organizations
B. Future developments
C. Impact of new technologies



Literature
Good summaries of the topic are presented in:

Therapeutic Applications of Monte Carlo Calculations in Nuclear Medicine
Ed. H Zaidi, G Sgouros, IOP Publishing, Bristol UK. ISBN 0750308168.

M. G. Stabin, R. W. Howell, and N.C. Colas-Linhart. Modeling radiation dose and effects from internal emitters in nuclear medicine: from the whole body to individual cells. Cellular and Molecular Biology 47(3):535-544, 2001.

M. G. Stabin, M. Tagesson, S.R. Thomas, M. Ljungberg, S.E. Strand. Radiation dosimetry in nuclear medicine. Applied Radiation and Isotopes 50:73-87, 1999.

Loevinger R, Budinger T, Watson E: MIRD Primer for Absorbed Dose Calculations, Society of Nuclear Medicine, 1988.

Siegel J, Thomas S, Stubbs J, Stabin M, Hays M, Koral K, Robertson J, Howell R, Wessels B, Fisher D, Weber D, Brill A. MIRD Pamphlet No 16 – Techniques for Quantitative Radiopharmaceutical Biodistribution Data Acquisition and Analysis for Use in Human Radiation Dose Estimates. J Nucl Med 40:37S-61S, 1999.

ICRU Report 67 Absorbed-Dose Specification in Nuclear Medicine, International Commission on Radiation Units and Measurements, 2002.

Jönsson L, Liu X, Jönsson B-A, et al. A dosimetry model for the small intestine incorporating intestinal wall activity and cross-doses. J Nucl Med. 2002;43:1657-1664.