Positron Emission Tomography/Computed Tomography (PET/CT) in Ovarian Cancer
Harpreet K. Pannu, M.D., Robert Bristow, M.D., Frederick J. Montz, M.D., Richard L. Wahl, M.D., Elliot K. Fishman, M.D.
Accurate detection of metastatic disease is important for staging and surgically treating ovarian cancer
Peritoneal metastases are most common –
Can be difficult to detect on bowel/diaphragmatic/pelvic viscera surfaces by CT
Can be difficult to distinguish from physiologic uptake in abdomen/pelvis by PET
Combined morphologic and functional imaging may –
Increase sensitivity for detection of disease
Increase confidence in diagnosing lesions as malignant on CT
Improve specificity of PET by distinguishing pathologic from physiologic activity
Improve localization of pathologic activity on PET
fifth most common malignancy in women
most common gynecologic malignancy to cause death
usually affects women over the age of 60 years.
Stage of disease
usually advanced (Stage III or IV) at presentation
Stage I: tumor limited to the ovaries
Stage II: extension into the pelvic tissues
Stage III: implants beyond the pelvis
Stage IV: distant or parenchymal liver metastases
Routes of spread
peritoneal fluid, lymphatics, and blood
peritoneal route is most common
common sites of implants are the pelvis, right hemidiaphragm, liver, right paracolic gutter, bowel and omentum
nodes involved are the iliac, retroperitoneal and inguinal nodes
Role of imaging
to determine extent of disease at presentation
to monitor for recurrence
Imaging of ovarian cancer:
Computed tomography (CT)
overall sensitivity for peritoneal metastases 85-93%
sensitivity for subcentimeter lesions 25-50%
rapid study, easily available, well tolerated
Magnetic resonance (MR)
equivalent to CT for detecting peritoneal metastases
sensitivity 91% for detecting recurrent or residual disease
Positron emission tomography (PET)
complementary test to CT/MR in patients with negative scans and rising tumor markers
variable sensitivities reported for detecting disease
subcentimeter lesions difficult to distinguish from bowel activity
combined imaging has the potential to improve detection of metastases
Principles of FDG PET imaging:
Increased glucose (18FDG:fluorine-18-fluorodeoxyglucose) uptake by cancer cells
FDG trapped inside cancer cells – 18FDG phosphorylated but not metabolized further
Decay of 18FDG molecule (t1/2 =110 minutes) – positron emitted and annihilates by colliding with an electron – 2 photons emitted at 180 degrees from each other and detected by opposing detectors to form an image
High tumor to background ratio on image
Lesions greater than 5-10 mm detected with dedicated PET scanner
18FDG uptake by cancer cells
increased with viable cells and adequate tumor perfusion
increased with acute chemotherapy and radiation inflammation
decreased with necrosis
decreased after effective chemotherapy and chronic radiation change
decreased in hyperglycemia due to competing unlabeled glucose molecules
18FDG uptake by non-cancer cells
increased in inflammatory cells
increased in normal brain, heart, exercising skeletal muscle
Technology and advantages of PET/CT:
Both PET and CT gantries in same physical location
PET scan immediately follows CT scan
similar stomach/colon/bladder content on both scans for accurate fusion of abdominal images
Common table for both scans
patient position similar for both acquisitions
no significant shift internal organs/change in body curvature
no need for external markers/extensive computer fusion algorithms
calibration of imaging coordinates of both scanners
Automated intermodality registration
improved alignment of data to within few millimeters in 3 translation dimensions
improved alignment of data to within few degrees in 3 rotation dimensions
more precise anatomic localization
increased reader confidence in lesion diagnosis
Use of CT for transmission scan
decreased study time
Technique for PET/CT:
fast 4 hours prior to scan – to lower insulin and blood sugar levels
avoid strenuous activity 1 day prior – to decrease skeletal muscle uptake
drink water for hydration – to enhance urinary excretion
recent surgery/biopsy – can increase uptake at surgical site
prior chemotherapy or radiation – can affect uptake
recent colony stimulating factors – can increase marrow uptake
administer 750 mL ionic oral contrast 1 hour prior to imaging – to opacify bowel on CT
inject 10-15 mCi 18FDG intravenously 1 hour prior to imaging – injection 1 hour prior to scanning improves tumor to background ratio
patient voids prior to imaging – to decrease bladder activity
patient positioned supine on table with arms up
iodinated intravenous contrast not administered as it may adversely affect attenuation correction map from transmission CT scan
scans acquired from skull base to mid thigh level during quiet respiration
CT performed with 4.25 mm thick contiguous slices, --- mAs, 140 kVp
PET performed with 5-10 minute acquisition per imaging level
Interpretation of PET/CT images
Normal activity on PET
most common sites – brain, myocardium, bladder 
workstation review of axial, coronal, sagittal images with varying gray scale, rotating views, and maximum intensity projection images 
review of CT, PET, and fused PET/CT images
qualitative determination of areas of pathologically increased uptake
calculation of standardized uptake value (SUV) of lesions 
SUV = [(mCi/mL in tissue) / mCi injected dose] X patient weight in gms
higher SUV (>3.25) suggestive of malignancy
rising SUV suggestive of tumor recurrence
SUV higher in obese patients and with smaller regions of interest (ROI)
Figure 1 59 year old woman with recurrent ovarian cancer. (a) Increased activity right and left pelvis greater than surrounding bowel on PET. (b) Small nodules in sigmoid mesocolon on CT but no definite mass right pelvis. (c) Fused image shows activity in sigmoid nodules and over cecum. Tumor found at both sites at surgery.
Figure 2 46 year old woman with recurrent ovarian cancer and elevated CA 125 to > 8000 U/mL. (a) Intense uptake in pelvis on PET. (b) Partially calcified masses on CT in left pelvis around bowel and superior to bladder. (c) Increased activity corresponds to pelvic masses compatible with tumor.
Figure 3 46 year old woman with recurrent ovarian cancer. (a) Increased uptake in left pelvis on PET - bowel implant vs node. (b) Enlarged left iliac nodes on CT. (c) Activity in left iliac nodes on fused image and nodes were malignant at surgery. Misregistration of bladder activity in right pelvis.
Figure 4 46 year old woman with recurrent ovarian cancer and elevated CA 125 to > 8000 U/mL. (a) Uptake in right upper abdomen along liver surface on PET. (b) Calcified liver implant on CT. (c) Uptake corresponds to tumor mass on fused image.
Figure 5 57 year old woman with recurrent ovarian cancer. (a) Curvilinear uptake in mass with cold center in right abdomen on PET. (b) Mass with cystic central and solid peripheral components on CT. (c) Solid areas demonstrate activity on fused image compatible with tumor.
Figure 6 59 year old with recurrent ovarian cancer. Increasing abdominal disease on CT and mediastinal adenopathy in setting of rising CA 125 likely due to metastatic disease. Increased uptake in enlarged nodes in the right paratracheal, bilateral hilar, subcarinal and prevascular regions on PET (a), CT (b), and fused (c) images.
Increased sensitivity for detection of disease on fused images
Figure 7 55 year old woman with ovarian cancer and rising CA 125. (a) Minimal nodularity left paracolic gutter on CT suspicious for implants. (b) Linear slightly increased uptake in same area on PET. (c) Increased activity on PET corresponds to nodules on CT and is suggestive of tumor implants.
Figure 8 59 year old woman with recurrent ovarian cancer. (a) No obvious mass adjacent to unopacified bowel on CT. (b) Small area of increased uptake midabdomen on PET. (c) Uptake localized to transverse colon on fused image. Tumor nodules involving transverse colon found at surgery.
Figure 9 46 year old woman with recurrent ovarian cancer and elevated CA 125 to > 8000 U/mL. (a) Inhomogenous distribution of oral contrast on CT results in some small bowel loops being unopacified. (b) Uptake in mass in midabdomen on PET. (c) Fused image localizes mass and allows distinction of tumor from adjacent bowel loops.
Figure 10 Pelvic recurrence vs postoperative collection. 75 year old woman with gross residual disease at second - look laparotomy 3 months prior to PET/CT. (a) Bilateral adnexal masses on CT. Mass on left is cystic and mass on right has near soft tissue attenuation. (b) Increased activity right pelvis on PET and photopenic area left pelvis. (c) Recurrent tumor right pelvis is hot on fused image and postoperative collection left pelvis shows no uptake.
Distinguishing pathologic from physiologic activity on PET
Figure 11 73 year old woman with primary surgery for ovarian cancer 4 weeks prior to PET/CT. (a) Surgical incision path seen in abdominal wall on CT. Increased uptake in abdominal wall on PET corresponds to the scar on axial (b) and coronal (c) fused images. Increased activity is due to inflammatory change secondary to recent surgery.
Figure 12 58 year old woman with recurrent ovarian cancer. (a) Cystic mass seen in left pelvis on CT. (b) Fused image shows activity right pelvis. (c) Inferior CT slice shows right pelvic activity is due to bladder. Activity seen on fused image in (b) is secondary to misregistration due to breathing. Left pelvic mass is a postoperative collection.
Figure 13 57 year old woman with recurrent ovarian cancer. (a) Increased uptake in left abdomen on PET. (b) Small peritoneal implant in same area on CT. (c) Activity on fused image is over the stomach and just medial to actual location of implant. Misregistration is due to breathing.
Figure 14 Foci of increased activity appear larger on PET than actual size on CT. (a) Both ureters are normal in size on CT. (b) Increased activity in the ureters causes larger areas of uptake to appear on the PET image. (c) Fused image shows ureteric activity superimposed on the left psoas muscle.
Anatometabolic imaging has the potential to improve the detection of metastatic ovarian cancer. Combined imaging can be used to diagnose disease with increased confidence on CT. Fusion of PET images with CT can improve localization of pathologic activity and distinction from physiologic uptake.
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