PET/CT PATIENT DOSE AND IMAGE
QUALITY
Olivera Šveljo1, Silvija Lučić2, Andrea Peter2,
Dejan Kozarski1, Miloš Lučić1
1Diagnostic Imaging Centre, Oncology Institute of Vojvodina,
2Department of Nuclear Medicine, Oncology Institute of Vojvodina
Sremska Kemnica,
Serbia
RAD2012, April 25-27, 2012
Niš
Hybrid PET/CT Imaging
• “Simultaneosly” obtains anatomical (CT) and functional
(PET) data
• Image fusion and CT based attenuation correction
instead of separately mesured data
• Increased clinical application – more and more scanners
being installed in hospitals and clinics worldwide
• Both (PET and CT) as stand alone are considered as
high dose diagnostic imaging procedure.
• PET/CT examinations increased patient radiation
exposure compared to stand-alone PET or CT
examinations
• PET/CT is a relatively new imaging modality and the
aim of this study was to clarify some aspects of this
complex diagnostic procedure regarding effective
patient dose and image quality
• Two sources of radiation:
– Internal dose from radiopharmaceuticals
(PET) and
– External from X-rays (CT)
CT
PET
Aim: to evaluate patient doses and CT image
quality for PET/CT examinations in a period of one
month in our Centre
•5 head examinations
– 4 female and one male (mean age 44,8±8,2,
range 35-55y)
•20 whole body examinations
– 5 female and 15 male (mean age
52,45±12,07; range 30-73y)
• Biograph 64 (Siemens, Erlangen, Germany)
• PET - 18F-FDG ([fluorine -18]-fluoro-2-deoxy-D-glucose)
– HEAD
• 10 min per bed position (one bed position)
– Whole Body
• 3 min per bed position (6-8 bed positions)
• CT
– HEAD
• Low dose spiral CT (120kV; sw 3mm; p 1.2; r 1s; AEC)
– Whole Body
• Low dose spiral CT (120kV; sw 5mm; p 1.2; r 0.5s; AEC)
• Total imaging time
– HEAD
• ~11 min
– Whole Body
• ~30 min
Internal dose calculation:
– Absorbed dose DT to a tissue organ T of
activity A of FDG:
DTPET  A  TFDG
ГTFDG- ICRP 80
– Overall internall effective doses:
EDPET   DTPET WT
T
WT – ICRP 103
External effective dose was calculated from
DLP acording to method proposed by Huda
et al.
EDCT  DLP   S
W. Huda, K.M. Ogden, M.R and M.R. Khorasani,
“Converting dose-length product to effective dose at CT”
Radiology 2008; 248(3): 995-1003
– Overall patient’s effective dose was
calculated according to:
ED  EDPET  EDCT
• CT image quality was assesed by
radiologiast with ten years of expirience
according to five point scale:
– 1 unacceptable,
– 2 substandard,
– 3 acceptable,
– 4 above average,
– and 5 superior
Effective patient dose and image
quality for Hybrid PET/CT imaging
AVERAGE
exam
head
Whole Body
internal dose
[mSv]
4.11±2.03
7.14±1.59
external dose
[mSv]
1.38
3.26±0.81
PET/CT
5.49±2.04
10.48±1.91
min/max
exam
internal
external
overall
min
max
min
max
min
max
head
2.42
6.54
1.38
1.38
3.81 7.92
Whole Body
4.64
10.78
2.20
4.97
6.85
15.67
• CT Image quality
– Head
• Rated with maximal score (5) for all exams
– Whole Body
• mean rate 3.8±0.8
All images were rated as acceptable or better, except in
extreme case of oversized patient who was not able to
hold arms above head
• Potential risk from radiation exposure is important aspect
in all medical procedure with ionising radiation
• PET/CT offers variety of imaging options with different
effective patient doses. It has bean reported that
combined dose for PET/CT exams could be up to 32mSv
• It also has bean reported that external dose compromise
50-81% of overall patient dose in hybrid PET/CT imaging
• Our survey shows that low dose CT protocols reduces effective
patient doses with out compromising CT image quality in majority of
the PET/CT exams.
• Minimal overall patient dose in our study was ~1.5 of worldwide
effective dose from background radiation over 1y [2.4mSv]
• Our results shows that using low dose AEC CT protocols external
dose could be decreased to ~ 30% of overall patient dose with out
compromising CT diagnostic image quality
• AEC CT protocols fail to meat criteria of diagnostically acceptable
image quality only in extreme case of obese patient who was not
able to hold his arm above head.
instead of conclusions
• Internal dose depends mainly on administered
radiopharmaceutical activity which is related to
patient body parameter and posibilities of
internal dose reduction for given PET modality
and given radiofarmaceutical are relatively small
• On the other hand CT offer wide variety of
imaging options and optimisations CT protocols
considering image quality and patient dose
provide a good basis for patient dose reduction
in PET/CT procedure
instead of conclusions
• Clinical demands for PET/CT diagnostics are increased,
especially for nononcological patients
• PET/CT scanning is accompanied by substantial
radiation dose and as a consequence potential cancer
risk. It is general recommendation that any PET/CT
examination should be carefully justified prior to any
study especially in younger patient.
• It is important to fully understood sources of patient
doses in PET/CT imaging and to clarify various
possibilities of dose reduction in order to rich full
diagnostic potential of this complex imaging modality.
Thank you!
Novi Sad