SUS-Malmö
Challenges in nuclear medicine
radiation dosimetry
Sören Mattsson
Medical Radiation Physics, Lund University and
Skåne University Hospital Malmö, Sweden
ICRP Committe 3
Nuclear medicine is expanding• Growing use of PET/CT and SPECT/CT (now also
PET/MRI)
• Oncology and also neurological and cardiac diagnostic
procedures
• Increasing use of radiotracers in surgical practices
• New radiopharmaceuticals (increasing importance
of shortlived radionuclides)
Nuclear medicine stands for a small number of
investigations compared to diagnostic radiologyExamples:
Globally (1997-2007): 1% of diagn radiological exams
Sweden (2005): 2%
USA (2006): 5% of investigations 26% of collective dose
_
_
_
_
_
1
10
100
0.1
0.01
PET/CT FDG, SPECT/CT, CT trauma (foetus)
CT colon
CT thorax/lungs SPECTCT head Low dose CT colonCT facial skeletonLow dose CT lungs
Low dose CT facial skeleton
99mTc-substances
Colon
Coronary angiography
UrographyLumbar spine
Mammography Lungs
Facial skeletonHand, foot
Teeth (single picture)
Effective dose, mSv
CT abdomen/pelvis, PET-FDG
PET/CT and SPECT/CT are
high-dose investigations
Nuclear medicine also for therapy
Small (Sweden 2010: 2.8%) in relation to nuclear medicine
diagnostic procedures
Therapeutic nuclear medicine
• Hyperthyroidism and thyroid cancer 131I-iodide
• Polycytemia 32P-orthophosphate
• Severe pain in metastatic bone disease 89Sr-chloride153Sm- or 177Lu-EDTMP186Re-EHDP223Ra-chloride
• Tumours (monoclonal antibodies and 90Y-Zevalin
peptides, receptor specific substances) 90Y-,131I-, 177Lu-, 211At-MaB
• Neuroendocrine tumours 131I-mIBG90Y-, 177Lu-octreotate
• Liver tumours 90Y-microspheres (SIRT)
Patients
TherapyNTCP/TCP for the INDIVIDUAL patient
stochastic risks; can not be assessed for an individual
patient, but for a population of patients
DiagnosticsStaff
Dosimetry in nuclear medicine
We want to know the absorbed dose in all irradiated tissues/organs
of interest
• Biokinetics
• Dose calculations (radionuclide decay, body geometry, organ volume, etc…)
Varying needs for accuracy in therapy and diagnostics
Therapy: better than +/- 5% (like external radiation therapy)
Diagnostics: +/- say 20%
Can we meet these needs for accuracy?
The major contributor to uncertainty in absorbed dose estimations
is the activity quantification and how frequently the
measurements can be done
Activity, A(t)
Time, t+
+
++
++
+
Biokinetics, A(t)• Quantification of activity in organs and tissues
• Blood and excreta
sampling
Methods:
1) Serial planar gamma camera imaging, conjugate view method
(geometric mean to anterior-posterior projections), attenuation and
scatter correction
2) SPECT(/CT) with attenuation and scatter corrections
3) PET(/CT) attenuation and scatter correction
Most
quantification
methods based
on iterative
methods
10 min 1 h 4 h 24 h 48 h
Sydoff et al., 2012
A patient measured at 5 times after injection of 123I-ioflupan
Sydoff et al., 2012
Ten 123I-ioflupan patients 10 minutes after injection
Booij et al., 1998
Mean activity in blood
Cumulated urinary excretion
(decay corrected)
BiokineticsAim: Detailed compartment models
Reality: Descriptive biokinetic models
• The biokinetics is often described as a sum of exponentials
• These are “net models” which describes what we can measure
• There is usually no unique transformation of a net model to a
compartment model. (This is possible only if the structure of the
compartment model is known).
111In octreotide
4 hours after inj. 24 hours after inj.
front frontback back
Activity A(rs,t)
Cumulated activity= ∫A(rs,t)dt = A(rs)~
Time
S - Source organ or tissue
Fs - Fractional distribution to S
T - Biological half-time for an uptake or
elimination component
a - Fraction of Fs taken up or eliminated with the
corresponding half-time. A negative value
indicates an uptake phase.
Ãs/Ao- Cumulated activity in S per unit of adm activity
Biokinetic data – Indium-labelled octreotide
From cumulated activities to organ/tissue absorbed dose
Computational models = ”Phantoms”
Diagnostics: ICRP Reference phantoms
Why?
To be able to compare information between hospitals
To be able to compare different investigation methods
Therapy:
Realistic phantoms tailored to the individual patient
Why?
Weight and lenght differ
Organ masses differ
Distances between organs differ
MIRD/ORNL Cristy and Eckermann Hermaphrodites
www.peddose.net
http://www.
virtualphantoms.
org/index.html
or tomo-
graphic
model
polygon
mesh
NURBS-
surfaces
Dose calculations
Protocols
Type of equipment/measurements
Image quantification (corrections performed; attenuation, scatter,
dead time, reconstruction parameters for SPECT or PET, background
subtraction)
Time points on time-activity curves. Integration
Bladder voiding interval
Dose computation model
For the effective dose calculation; Set of tissue-weighting factors
Number of participant in the study
1998
(printed late 1999)
ICRP Publication 80
(Addendum 2)10 new radiopharmaceuticals
+ recalculations of 19 frequently
used ones in Publ 53.
ICRP Publication 106
(A third amendment)33 radiopharmaceuticals in current
use. Recommendations on breast
feeding interruptions.
2008Task Group:
S. Mattsson
L. Johansson
B. Nosslin
T. Smith
D. Taylor
E/A0, µSv/MBq
99mTc-substances
0.001 0.01 0.1
99mTc-colloids (small), intratum. inj.
99mTc-pertechnetate, with blocking
99mTc-apticide
99mTc-DTPA
99mTc-phosphates and phosphonates
99mTc-EC
99mTc-MAG3
99mTc-RBC
99mTc-tetrofosmin (rest/exercise)
99mTc-ECD
99mTc-MIBI (rest/exercise)
99mTc-DMSA
99mTc-HM-PAO
99mTc-colloids (large)
99mTc-furifosmin
99mTc-MAB
99mTc-MAA
99mTc-WBC
99mTc-pertechnegas
99mTc-pertech, without blocking
99mTc-IDA derivatives
99mTc-markers, non-absorb per os
99mTc≈ 0.008 µSv/MBq
0.001 0.01 0.1
15O-water
82Rb-chloride
11C-thymidine
11C-acetate
11C-brain rec subst (generic mod)
11C-choline
11C-amino acids (generic mod)
11C-methionine
11C (realistic max mod)
18F-FLT
18F-FET
18F-choline
18F-FDG
18F-amino acids (generic mod)
18F-fluoride
18F-L-dopa
18F-brain rec subst (generic mod)
PET-substances
18F≈ 0.02 µSv/MBq
11C≈ 0.005 µSv/MBq
E/A0, µSv/MBq
E/A0, µSv/MBq
201Tl- 131,125,123I-, 111In-, 75Se-, 67Ga-, 51Cr-, 14C-, 3H-substances
0.001 0.01 0.1 1 10 100
51Cr-EDTA123I-MIBG
123I-fatty acids123I-iodide, after ablation, 1%
123I-MAA14C-urea (normal)
123I-brain rec subst (generic mod)131I-iodo hippurate
111In-octreotide67Ga-citrate
201Tl-chloride111In-MAA
3H-fat 123I-iodide, 35% thyroid uptake
131I-MAA131I-iodide, after ablation, 1%
75Se-HCAT14C-fat
131I-iodide, 35% thyroid uptake
11C 18F99mTc
0.001 0.01 0.1 1 10 100
14C-urea (normal)51Cr-EDTA
131I-iodo hippurate75Se-HCAT (low bg)
14C-urea (Helicobacter pos.)3H-fat
99mTc-colloids (small), intratum. inj.14C-fat
75Se-HCAT99mTc-pertechnegas
15O -water 99mTc-markers, non-absorbable (fluids) per os99mTc-markers, non-absorbable (solids) per os
99mTc-DMSA99mTc-MAG3
11C-thymidine 99mTc-DTPA
11C-amino acids (generic model) 11C-brain receptor substances (generic model)
99mTc-MAA11C-choline
99mTc-pertechnetate, with blocking99mTc-WBC
123I-iodide, 35% thyroid uptake 123I-fatty acids (BMIPP/IPPA)
99mTc-MIBI (rest)11C-methionine
99mTc-IDA derivatives11C-acetate
99mTc-colloids (large)82Rb-chloride
99mTc-phosphates and phosphonates99mTc-apticide
99mTc-EC99mTc-ECD
123I-MAB11C (realistic maximum model)
99mTc-tetrofosmin131I-iodide, 35% thyroid uptake
99mTc-MIBI 123I-MIBG
99mTc-furifosmin (exercise)99mTc-RBC
99mTc-pertechnetate, without blocking99mTc-furifosmin (rest)
123I-iodide, after ablation, 1% thyroid uptake18F-FDG 18F-FLT 18F-FET
99mTc-HM-PAO18F-choline99mTc-MAB
123I-brain receptor substances (generic model)18F-amino acids (generic model)
111In-octreotide18F-fluoride18F-L-dopa
18F-brain receptor substances (generic model)201Tl-chloride
67Ga-citrate 131I-iodide, after ablation, 1% thyroid uptake
111In-MAB131-MAB
131I111In67Ga201Tl
18F123I99mTc11C
99mTc14C3H
Effective dose per investigation, mSv
Can we meet the accuracy requirements?
Therapy: No and Yes?
Diagnostics: Yes and No
Serial planar imaging scans + SPECT in combination +/- 10-20%
PET +/- 10% if very accurate attenuation, scatter and random
corrections
“…the accuracy of quantifying the concentration of a radionuclide
in regions within the body can be < 5% with SPECT or PET
imaging, and provided there are no overlapping structures
containing radioactivity, similar accuracy can also be obtained
with planar gamma camera imaging” (Frey et al., 2012)
Challenges (Diagnostics):
•For some substances biokinetic data are old (more than 20
years). Need to generate new data on biokinetics and
dosimetry using state-of-the-art equipment
•Few subjects per study. More volunteers are needed.
•Biokinetic data for children
•Biokinetic data for various ages
•Gender specific data
•Biokinetic data for ill
•More uniform dosimetry protocols
•Dose distributions within organs and tissues
•Review of CT protocols for SPECT/CT and PET/CT imaging.
DRLs
•Epidemiological studies
Challenges (Therapy):
•Dose planning before therapy, No therapy without dose
planning!
•Individual patient biokinetics
•Individual dose calculations
•Dose distributions within organs and tissues
•Same protocol for different hospitals and clinics for
measurements of biokinetic data and for dosimetry
•A formalism for the addition of doses from nuclear
medicine therapy and external radiation therapy for
patients receiving both treatments (BED)
Thank you for listening! … and don´t forget to collect biokinetic data
from your patients!
Task Group on Radiation Dose to Patients from Radiopharmaceuticals
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