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NMT » Case Studies » Current Case

Evaluation of Colorectal Cancer with PET/CT

Dorothy Pettay

Senior Nuclear Medicine Student Technologist
Medical College of Georgia

Asad Nasir M.D.
PET Fellow
Emory University Hospital

 

Chart

Patient History

The patient is a 57 year old female with known colorectal cancer Stage III (cancer has spread to lymph nodes either regional or apical/vascular trunk nodes). She has had a right hemicolectomy (surgical removal of half or less of the colon). This exam was compared to a PET/CT scan done 3 months prior. She has been receiving chemotherapy. This study is a restaging scan to determine the effectiveness of the chemotherapy.

Instrumentation

 

PET/CT General Electric LS (Light Speed CT) Camera

BGO crystal

 

 

Processing

GE SOFTWARE performs the processing (PET/CT fusion and CT attenuation correction for the PET) and the display software is Xeleris.

 

Radiopharmaceutical:

F-18 FDG: 2-[F-18]-fluoro-2-deoxy-D-glucose. F-18 is produced by a cyclotron and has a half-life of 110 minutes.

 

Biodistribution F-18 FDG is excreted through the renal system. There is normal high uptake in the brain, kidneys, bladder, sometimes the heart (left ventricle) and less uptake in the salivary glands, tonsils, thyroid, breasts, liver, spleen, bowel and stomach. {Also see the Imaging chart}

RpH characteristics:

18-F FDG is an ideal oncology agent. Cancer cells use more energy than regular cells since they go through rapid division. Because of the increase need of glucose, more 18-F FDG is taken up in malignant cells. 18-F FDG is processed like glucose. The process of glycolysis begins with hexokinase (first enzyme in this process) adding a phosphate group to the glucose part of 18-F FDG. The glycolysis of 18-F FDG stops at this point, and cannot pass through the cell membrane, thus is trapped inside.

 

Patient Prep:

Nothing to eat or drink except water after midnight. [Fasting causes the cells to increase their uptake of glucose, especially the malignant cells.] No intense physical activity for 24 hours prior to exam or there will be increased muscle uptake of the 18-FDG. [If patient is diabetic, they are advised to fast overnight and get an early morning appointment. If they cannot fast, then eat breakfast and take insulin, and schedule an early afternoon appointment.]

 

Procedure

 

Patient is brought into a room and a history is taken, positive ID, exam process explained and questions answered. Bottle of 450 ml of Oral contrast (barium) is given. This defines the GI tract and helps the reading physicians to determine anatomy. {In this particular case, oral contrast was not given because the patient refused.} A butterfly needle system is placed in a vein and blood is drawn to check the glucose amount. If blood glucose is too high, the tracer will not be taken up by the cells because of competition between blood glucose and F-18 FDG glucose. If the blood glucose value is below 180mg/dl, the injection of 15 +/- 10% mCi of 18-F FDG is then done. A syringe shield is used for the protection of the technologist. Saline is used to rinse the syringe, by use of a 3-way stopcock. The amount of tracer is carefully checked and time noted. The time of injection is noted and then residue of tracer (in syringe) is determined along with the time. This is entered in the computer at time of imaging along with the weight and height of patient. (Reason for this will be discussed with the SUV discussion). The patient is instructed to relax in recliner and rest. If too much movement, there will be muscle uptake of the tracer. A warm blanket is provided if desired. If head/neck cancer is being studied, a warn towel is place over head and around neck prior to injection and during the hour of wait. This decreases the uptake of tracer in brown fat. This uptake can look like lymphoma to an untrained eye. After 30 minutes the patient is given another bottle of barium, if they can tolerate it. After 1 hour, the patient is instructed to empty their bladder (tracer is excreted through the renal system and a full bladder will decrease visibility in the pelvic area).

 

Positioning

Patient lies supine on the PET/CT scanner table, with cushion under knees for comfort and blanket is provided if desired. A band is placed around head and table to help patient keep head straight (especially if they fall asleep). The top of head is “marked” by a laser light. This tells the scanner where to begin the images. The patient’s arms are placed above head so there is no added attenuation around the chest area. (If the study is a head and neck, the arms are down and placed on abdomen with hands over the pelvis area, so the head and neck area has no added attenuation, this is also done if the patient cannot tolerate arms above head for the scan). The patient is instructed to remain still during the scan.

A scout CT is done first and from this the number of beds are determined. Bed placement is placed at just above the eyes down to thighs. The brain is not included (unless head/neck cancer, melanoma or if MD orders to include head) because of normal high uptake of tracer. Each bed takes 4 minutes and covers ~15 cm of the body/bed. Then the CT scan (~1 minute) is done. It is before the PET because of the possibility of patient movement during the PET scan (20-30 minutes) and is also used in attenuation correction. This provides a “map” of the body. Then the PET scan is done. Average patient is 6-7 bed lengths when scanning eyes to thighs.

 

 

Considerations for the reader

WHAT’S IMPORTANT FOR THE READING PHYSICIAN? WHAT DO THEY LOOK FOR WHEN READING THIS PATHOLOGY? ANY TECHNICAL CONCERNS? The Nuclear Medicine physician looks at the images alongside the most recent previous images if available. They mainly look at the transverse images. They start with the brain and go to the end looking at the fused PET/CT and the CT at the same time. If there are any areas with an increase of F-18 FDG uptake, they look at the CT to see what tissue is involved and if it appears to be normal uptake or suspicious tissue. They compare the liver to the spleen. Spleen should have less uptake than the liver. They look at the SUV (standardized uptake value). SUV is calculated by mean selected region activity (mCi/ml)/[Injected dose (mCi)/body weight (kg)]. SUV normalizes the FDG accumulation in a region of interest to the total injected dose and body weight. It provides a means of comparison of FDG uptake between patients. An SUV greater than 2.5 is considered to be an indicator for malignancy (www.auntminnie.com). Since this patient has had colorectal cancer, the physician looks closely at the area of the colectomy for any increased uptake, and then the lymph nodes of the abdomen. Any areas in prior scans with increased uptake are compared to evaluate an increase or decrease SUV to determine if chemotherapy is working. This patient has been receiving chemo treatments and the scans are for restaging.

 

 

Findings—Report reads:

Impression:

1. Increased size and FDG uptake in the retroperitoneal nodal conglomerate suspicious for progression of disease. [In the report it was noted that the size is now 5.5 cm and the prior was 5.0 cm and an increase of SUV uptake from 7.0 to 9.0.] See images below.

 

Small arrows pointing to the periaortic retroperitoneal lymph node conglomerate in the coronal, sagittal and transaxial views.
Red arrow: heart.
Blue arrow: bladder.
Green arrow: kidney of the MIP image. The MIP image has the body turned a little to the right to visualize the lymph node conglomerate. This could be mistaken for the right kidney, thus it is important to look at all views. The transaxial view shows the conglomerate in relation to the kidneys. This is also seen well in the next image below.

 

White arrow: lymph node conglomerate. Green arrow: right kidney

2. Whole-body FDG PET-CT from the skull base to the mid-thighs demonstrates 2 new pulmonary lesions, one of which has a speculated margins and demonstrates mild increased FDG uptake, suspicious for new pulmonary metastatic deposits. [In the image, the nodule looks the same as the other lung markings, however if you go up and down through the images, you will see the lung markings following a “line” where the nodule is alone.] See images below.

 

Black arrows: small lung nodule.
Red arrow: heart.

 

3. Linear focus of uptake within the anterior intra spinal canal at the thoracolumbar junction extending over 2 to 3 vertebral bodies. The finding is not associated with CT abnormalities and may be a functional abnormality related with tumor involvement of the celiac plexus. (No images)

 

 

Prior Studies

 

The patient had a PET/CT 3 months and 5 months prior to this one. These two were compared.

Impression:

 

1. A stable right periaortic hypermetabolic lymph node conglomerate. No other areas of abnormal FDG uptake identified.

 

2. In view of neuroendocrine feature in histology, consider In-OctreoScan/ or I-123 MIBG to evaluate for Sandostatin or I-131 MIBG therapy.

 

 

Patient had an I-123 MIBG Whole Body Scan:

 

Impression:

 

1. Bilateral physiologic adrenal gland uptake.

 

2. Possible faint uptake in previously demonstrated PET avid periaortic lymph node, below threshold for treatment with MIBG.

 

3. No focal MIBG avid lesions in the liver.

 

 

Discussion

Colorectal cancer is the third most common cancer in Western countries and is the second leading cause of cancer related deaths (Wikipedia.com). It is seen most often in the age group of 60-75. Colon cancer is most common in women and rectal cancer is most common in men. Most cases are adenocarcinomas (epithelial-glandular tissue) (Merck.com). Adenomatous polyps in the colon start out as benign but in some cases the polyps will develop into cancer over a period of a few years. This is why colonoscopies are recommended for people over the age of 50 (younger if family history of colorectal cancer). If a polyp is found during the exam, it can be removed, thus removing the possibility of cancer development. Metastatic colorectal cancer is found most often in the liver and sometimes in the lungs, bones or brain (WebMD).

 

Copyright 2009 Medical College of Georgia All rights reserved.

Biomedical & Radiological Technologies | School of Allied Health Sciences Please email comments, suggestions or questions to: Mary Anne Owen, mowen@mcg.edu. April 14, 2009