Introduction Materials and Methods Results and Discussion Conclusions

Internal exposure arising from intravenousadministration of F-18 fluorodeoxyglucose

A. Beganovic1,2, M. Modronja, S. Odzak2,A. Skopljak-Beganovic1, M. Gazdic-Santic1

1University Clinical Centre of Sarajevo, 2Faculty of Science Sarajevo

14 March 2015

Internal exposure arising from F-18 FDG UKCS/PMF

Introduction Materials and Methods Results and Discussion Conclusions

Contents

Introduction

Materials and Methods

Results and Discussion

Conclusions

Internal exposure arising from F-18 FDG UKCS/PMF

Introduction Materials and Methods Results and Discussion Conclusions

18F Fluorodeoxyglucose

Fig. 1 : Stereo skeletal formulaof fluorodeoxyglucose (18F)((2S,6R)-6-meth,-2-ol)

I 18F fluorodeoxyglucose (FDG) is aradiopharmaceutical widely used inpositron emission tomography(PET) imaging.

I FDG is labeled with 18F apositron emitting radioactiveisotope (T1/2 = 110 min).

I It is a glucose analogue chemically similar to the glucosesugar.

Internal exposure arising from F-18 FDG UKCS/PMF

Introduction Materials and Methods Results and Discussion Conclusions

Properties of 18F

I 18F is produced in medicalcyclotrons (Fig. 2) by protonbombardment of 18O-enrichedwater

I After the decay most positronsgo through annihilation processwith orbital electrons, whichresults in two 511 keV gammaphotons moving in oppositedirections. Fig. 2 : Medical cyclotron in

Bologna University Hospital

Internal exposure arising from F-18 FDG UKCS/PMF

Introduction Materials and Methods Results and Discussion Conclusions

Positron emission tomography (PET)

Fig. 3 : Ring of detectors used inPET (Bi4Ge3O12 crystals), UKCS

I PET is an imaging techniquethat uses detection (Fig. 3) ofopposing photon pairs toproduce functional image of thehuman body.

I If used with 18F-FDG, PET willdetect areas with high glucoseuptake, such as the brain, heart,liver, and most cancers.

I Gamma rays also contribute tothe exposure of patients toionizing radiation.

Internal exposure arising from F-18 FDG UKCS/PMF

Introduction Materials and Methods Results and Discussion Conclusions

Radiation exposure

I Dose received by patients undergoing PET examination arisesfrom internal exposure.

I In order to evaluate the effective dose, the quantity mostconvenient for the purpose of comparison with otherdiagnostic modalities, one needs to know average absorbeddose (DT ) to every radiosensitive organ in the human body.

E =

wRwT DT (1)

I Weighting factors wR and wT in Eq. (1) are radiation andtissue weighting factors, respectively.

Internal exposure arising from F-18 FDG UKCS/PMF

Introduction Materials and Methods Results and Discussion Conclusions

Effective dose estimation

I Effective dose represents thestochastic health risk (probabilityof cancer induction and geneticeffects)

I It cannot be measured directly, butrather can be estimated.

I All modern estimation tools dependon Monte Carlo simulations.

I Patients body is represented withone of the available computationalhuman phantoms.

Fig. 4 : VIP-Man phantom(Rensselaer PolytechnicInstitute in Troy, NY)

Internal exposure arising from F-18 FDG UKCS/PMF

Introduction Materials and Methods Results and Discussion Conclusions

Medical Internal Radiation Dose Committee Method

I MIRD method of effective dose estimation relies oncalculation of absorbed dose from radioactivity distributedthroughout the source organ

I The cumulated activity As in a source organ is calculated byintegrating the activity over time:

As =

0

As(t) dt (2)

I The absorbed dose to a target organ Dt is calculated from:

Dt =s

AS(t, s) (3)

where S(t, s) is the mean absorbed dose to the target organfrom unit activity of the relevant radioisotope.

Internal exposure arising from F-18 FDG UKCS/PMF

Introduction Materials and Methods Results and Discussion Conclusions

Radioactivity calculation

I The crucial part of effectivedose estimation iscalculating/measuring the valueof cumulated activity, As, thatdepends on instantaneousactivity A(t).

I This value can be obtainedfrom PET images at a specifictime (ti 1 h after theinjection of FDG).

I Selection of the appropriateregion of interest (ROI) willgive us the uptake value.

Fig. 5 : Region of interest (volume)in the liver. Average uptake is3.6(4) kBq ml1

.Internal exposure arising from F-18 FDG UKCS/PMF

Introduction Materials and Methods Results and Discussion Conclusions

Calculation of cumulative activity

I In order to obtain the cumulative activity As(t) one needs toknow how the biological distribution of 18F was changing overtime not an easy task.

I We used the conservative approach:I 18F decays in human body with physical half-life (110 min)I time of accumulation in all organs is reduced to zero

I This method greatly simplifies the function A(t):

A(t) = A(0) 2t

T1/2 (4)

I The integral in Eq. (2) is now easily solvable.

Internal exposure arising from F-18 FDG UKCS/PMF

Introduction Materials and Methods Results and Discussion Conclusions

OLINDA/EXM vs. Radar

I Calculations continued using OLINDA/EXM Monte Carlocalculation software that utilizes estimated cumulative activityin order to obtain the effective dose, E.

I Input parameters include:I radionuclide used,I computational phantom (male, female, etc.)I kinetics (biodistribution over time)I residence time, , equal to ratio of cumulative activity and

activity administered:

=AsA0

(5)

I Simpler, but compatible software tool Radar was used tocheck the obtained results.

Internal exposure arising from F-18 FDG UKCS/PMF

Introduction Materials and Methods Results and Discussion Conclusions

Data collection methods

I Uptake values were sampled usingeither free shape or spherical ROI.

I Average uptake values (kBq ml1)were collected for source organswith high activity present, namely:brain, heart, liver, kidneys, urinarybladder, and spine. The uptake forthe remainder organs was sampledin the area of shoulder (lowactivity).

Fig. 6 : Uptake sampling

Internal exposure arising from F-18 FDG UKCS/PMF

Introduction Materials and Methods Results and Discussion Conclusions

Average uptake values

I 36 patients were assessed (18 females and 18 males)I All patients were administered with approx. 350 MBq of 18F

FDG.

I Average uptake values are given in table below.

Organ Volume (ml) Uptake (kBq/ml)

Urinary bladder 200 63.10Liver 1830 6.86Bones 6850.7 7.26Heart 437 9.63Brain 1370 16.18Kidneys 288 12.68Remainder 66 400 1.64

Internal exposure arising from F-18 FDG UKCS/PMF

Introduction Materials and Methods Results and Discussion Conclusions

Effective dose

I OLINDA/EXM estimated the effective dose of 7.0 mSv formale patients, and 8.3 mSv for female patients.

I Online software Radar used to check the results obtainedsimilar results: 6.8 mSv and 6.7 mSv, for male and femalepatients respectively.

I In general, the results obtained correspond to the values foundin literature. However,

I OLINDA/EXM works with female computational phantomwhich takes into account increased radiosensitivity of femaleorgans (breasts), which in turn makes the effective dose higher.

I Other differences might be caused by the conservativeassumptions.

Internal exposure arising from F-18 FDG UKCS/PMF

Introduction Materials and Methods Results and Discussion Conclusions

Conclusions

I OLINDA/EXM can be used with uptake values taken fromPET images to estimate the effective dose within satisfactoryaccuracy.

I Although same results can be achieved using simpler solutions,true value of the methodology used will be emphasized in thespecial circumstances (i.e. accidental or unknown exposures)when more unknown variables are present.

I Results can be improved by better modelling of activitykinetics (true shape of A(t) for each organ).

I Attention should be given to the reconstruction parameters asthey could affect the values of uptake.

Internal exposure arising from F-18 FDG UKCS/PMF

Introduction Materials and Methods Results and Discussion Conclusions

Internal exposure arising from F-18 FDG UKCS/PMF

IntroductionMaterials and MethodsResults and DiscussionConclusions