Monday Case of the Day
Alexander S. Pasciak, PhD, Austin C. Bourgeois, MD and Yong C
Physics
Bradley, MD University of Tennessee Medical Center, Knoxville, TN
History:
Patient with focal intrahepatic cholangiocarcinoma (Fig 1) treated with 90Y
radioembolization. Immediately following 90Y treatment, a bremsstrahlung
SPECT scan (Fig 2) and a PET/CT scan (Fig 3) were acquired. No
administrations of radioactivity other than 90Y were performed on treatment
day. Select the best clinical assessment and underlying physical reason.
A)
B)
Figure 1 (above): pretreatment 18FDG PET
acquired 48 hours before
treatment.
Figure 2 (above): posttreatment bremsstrahlung
SPECT
C)
D)
Figure 3 (right): posttreatment 90Y PET/CT
The treatment was successful: The
bremsstrahlung SPECT (Fig 2)
indicates that 90Y was deposited in the
tumor.
The treatment was not successful:
The 90Y PET/CT (Fig 3) shows poor
tumor uptake and significant nontarget hepatic embolization.
The treatment was not successful:
The bremsstrahlung SPECT (Fig 2)
shows radioactivity outside of the liver
in the stomach.
Neither post-treatment image is valid.
90Y is a pure 𝛃 emitter and cannot be
imaged using SPECT or PET.
Findings:
Analysis of the post-treatment bremsstrahlung SPECT appears to
indicate 90Y uptake in the tumor as well as the normal hepatic
parenchyma of the left lobe. The bremsstrahlung SPECT also
indicates apparent non-target embolization of extrahepatic structures
(Figure 2, arrows).
Figure 1: pre-treatment 18FDG PET acquired 48
hours before treatment.
Figure 2: post-treatment bremsstrahlung
SPECT
Findings:
Figure 1: pre-treatment 18FDG PET acquired 48
hours before treatment.
Figure 3: post-treatment 90Y PET/CT
Analysis of the post-treatment PET/CT
scan shows different result than the posttreatment bremsstrahlung SPECT. The
PET scan demonstrates very poor
uptake in the tumor (Figure 3, arrow)
with the majority of the radioactivity
deposition occurring in the normal
hepatic parenchyma. The PET does not
indicate that there is any extra-hepatic
non-target embolization.
The activity distribution as indicated by
the PET/CT (Figure 3) does not match
pre-treatment planning intentions (Figure
1).
Diagnosis:
(B) The treatment was not successful: The 90Y PET/CT shows
poor tumor uptake and significant non-target hepatic
embolization.
Figure 1: pre-treatment 18FDG PET acquired 48
hours before treatment.
Figure 3: post-treatment 90Y PET/CT
Discussion:
90Y
can be imaged effectively using PET/CT. In approximately 32
out of every 1 million decays of 90Y, a positron is emitted through a minor decay branch
[1]. A 20 minute post-radioembolization PET/CT scan of the liver is sufficient to produce
images which are superior (Figure 3) to traditional bremsstrahlung SPECT imaging of
90Y (Figure 2).
Figure 1: pre-treatment 18FDG
PET acquired 48 hours before
treatment.
Figure 2: post-treatment
bremsstrahlung SPECT
Figure 3 (right): posttreatment 90Y PET/CT
Discussion:
With positrons emitted by 90Y in only 32 out of every 1,000,000
decays, how can high quality images be produced?
For routine PET/CT imaging using 18FDG, positrons are emitted in 97% of decays. The
low branching fraction for positron emission following decay of 90Y has the potential to lead
to low count rates and noisy images.
However, several factors partially make up
for this:
Figure 3 (right): post-treatment 90Y
PET/CT
1. Higher activities of 90Y are traditionally
used (typically greater than 30 mCi)
compared to 18FDG (10-15 mCi).
2. The activity is concentrated in a much
smaller volume (tumor and liver
volumes typically less than 1 liter,
compared to 18FDG which is distributed
through the whole patient.
3. Modern 4-ring PET/CT scanners can
typically image the entire liver with just 1
bed position. A 20-30 minute scan of
just the liver is possible in a clinical
setting, compared with 2-4 minute bed
positions for clinical 18FDG imaging.
Discussion:
90Y
Bremsstrahlung SPECT images acquired with a wide window
have poor image quality and are often useful only for confirming that the treatment was
delivered to the target lobe (Figure 2). This is primarily due to the large amount of
scattered radiation which is included in the images.
The excellent resolution and contrast recovery of 90Y of PET/CT allows the treatment to
be localized far more effectively (Figure 3) compared to traditional wide window
bremsstrahlung SPECT imaging of 90Y (Figure 2). 90Y PET/CT also has the benefit of
being quantifiable in a clinical setting, allowing for image based dosimetry [2,3].
Figure 2: post-treatment bremsstrahlung
SPECT
Figure 3 (right): post-treatment 90Y
PET/CT
Clinical Summary:
Radioembolization capitalizes upon increased arterial
tumor vascularity of a target lesion compared to background liver tissue. Although
cholangiocarcinoma is a relatively hypovascular malignancy, this case represents a rare
instance in which the target lesion was actually LESS vascular than surrounding normal
hepatic parenchyma. Consequently, the tumor-absorbed dose was well below predicted
tumoricidal thresholds. The higher spatial resolution of the 90Y PET/CT allowed for early
identification of this treatment failure. In such cases, triage to alternative or adjuvent
interventional therapies such as radiofrequency ablation or chemoembolization could
help delay progression of disease.
Figure 1: pre-treatment 18FDG PET acquired 48
hours before treatment.
Figure 3: post-treatment 90Y PET/CT
References/Bibliography:
1A.
S. Pasciak, A. C. Bourgeois, J. M. McKinney, T. T. Chang, D. R. Osborne, S. N. Acuff
and Y. C. Bradley; Radioembolization and the dynamic role of 90Y PET/CT; Front.
Oncol; vol. 4:38, 2014.
2 D’Arienzo
M, Chiaramida P, Chiacchiararelli L, Coniglio A, Cianni R, Salvatori R, et al.
90Y PET-based dosimetry after selective internal radiotherapy treatments. Nucl Med
Commun; vol. 33(6):633–40, 2012.
3 A.
S. Pasciak, A. C. Bourgeois and Y. C. Bradley; A comparison of techniques for 90Y
PET/CT image-based dosimetry following radioembolization with resin microspheres;
Front. Oncol; vol. 4:121, 2014.