I'll Be Back - 2014

Sorry... I have been neglecting my BLOG.... not really, but I have some interesting cases to post for the students.  Just getting the time to work through the cases is difficult - but I'm still keen.

My last post was March 2013... shame, I know.  My New Years resolution is to update this Blog on a regular basis, since in the New Year I'll have some flexibility in developing educational content for the school that I am moonlighting with now.

Fig. 1  Here is something that we do not see very often.  Really interesting location for lymphoma.  I assure you that this was not from a spill practical training course.

In-111 Pentetreotide Imaging

I have had a lot questions with regards to In-111 pentetreotide imaging by my students since we have block bookings once a month to accomodate some of the physicians' requests for these scans.  Sometimes when I start talking about somatostatin and somatostatin receptors I get this glazed look in their eyes.

The best place to start would be to look at the Society of Nuclear Medicine procedural guidelines (SNM), since it would provide a grand overview of what this type imaging is all about.

We need to make the distinction between pentetreotide versus octreotide when discussing the imaging aspects, however.  In nuclear medicine the In-111 pentetreotide is the compound that we work with, because it has a DTPA chelator attached to it to allow it to bind to the indium-111 isotope.  Essentially pentetreotide (In-111-DTPA-D-Phe) is a conjugated form of a somatostatin analog.  Octreotide on the other hand is just a peptide (an octapeptide to be exact) that mimics the natural somatostatin that is found within our bodies.  Basically, octreotide is a synthetic version of the natural ones within our bodies.

Fig. 1  This is the pentetreotide peptide.  For those who would want to know what it looks like.

Fig.  2  This is the structure for Octreotide.  I will say this:  I am not a radiochemist, or a radiopharmacist and I did not take organic nor inorganic chemistry.  However, I made sure our radiopharmacist was okay with these images before posting.

Here are some images that we have acquired recently.  It will help us with the discussion.

Fig. 3  A 24 hour In-111 pentetreotide scan of a patient with gastrinoma.  Notice a focal uptake in the midline of the body, along with a faint uptake in the liver.  You can see it better in the whole body images on the right.

Fig. 4  Another 24 hour whole body imaging.  Note the focal uptake in the midline of the body.  This patient was being worked up for insulinoma.

Fig. 5  As above, imaging was performed at 24 hours.  However note the uptake in the thyroid.

Majority of the patients that come to see us receive an In-111 pentreotide injection for some type of neuroendocrine imaging.  Most of them involve the gastroenteropancreatic (GEP) tumours such as the insulinomas, gastrinomas, VIPomas (vasoactive intestinal polypetide secreting tumour) and other times we get the occasional request for carcinoids.  

Patient preparation is fairly straight forward, but one thing that is interesting is the decision to infuse glucose in patients in those suspected of insulinoma.  This is to prevent the potential problem of hypoglycemia during the injection.  It is not common practise and it is the decision of the radiologist to incorporate this in their standard of practise with these cases.  We do not do it at our site.  The one thing that we do screen for are medications, such as the use of Octreotide as a therapeutic agent.  Since Octreotide is the synthetic form of somatostatin within our bodies, it's more potent and effective in suppressing gastrin, cholecystokinin, glucagon, TSH, pancreatic polypeptide, secretin, growth hormone, TSH and vasoactive intestinal peptide.  Careful consideration of the time when the patient had taken the Octreotide is important as we want to ensure good uptake of the In-111 pentetreotide.  More patient preparation information can be reviewed in the SNM guidelines, or in the European Association of Nuclear Medicine guidelines as well.

The imaging of these patients are fairly straight forward as well.  Whole body scanning is generally done at 24 hours, but before when we had purchased our SPECT/CT, the standard of practise was to perform whole body imaging as well as, a standard SPECT at 48 hours.  The SPECT/CT was a bit of a game changer for us, since our radiologists were comfortable with the images obtained at 24 hours that included the SPECT/CT.

Not all these tumours are created equally.  In order to be visualized they require a number of somatostatin receptors on the tumours themselves. There are 6 known receptors:  SSTR1, SSTR2a, SSTR2b, SSTR3, SSTR4, SSTR5.  Note there are also subtypes as well.  With the "lock and key" method of visualization, the sensitivity of the tumours will vary.  For example, there is better sensitivity in gastroenteropancreatic neuroendocrine tumors (download the PDF, it's free), except for insulinomas as the result of the lower incidence of somatostatin receptors, especially those of the SSTR2.  The sensitivity is approximately 25-60% in comparison to the other tumours in this category.  The best practise for our department is that our radiologists screens the requisitions before we begin the bookings and the ordering of indium-111 for compounding.  

I want to touch upon one thing however and it is the biodistribution of the In-111 pentreotide.  Generally the normal uptake of In-111 pentreotide occur in the pituitary glands, the thyroid, liver, spleen, kidney, bladder and sometimes gallbladder.  Bowel is also seen but more so after 24 hours post injection.  If you look at Figure 5 in comparison to the other images, there is the obvious uptake in the thyroid bed.  I personally have not seen this very often, so my initial inclination was "abnormality" since medullary thyroid cancers and pituitary adenomas express high amounts of somatostatin receptors.  Upon reviewing the finalized report, it did not mention the uptake in the thyroid bed, but rather indicating no evidence of any octreotide avid pancreatic tumours or metastases; the biodistribution was normal.  Further review into the patient history, just recently, had the patient to undergo an urgent thyroid ultrasound and aspiration for pre-op staging.  This patient had a previous biopsy of the left thyroid as well, but it had unsatisfactory cellularity in the sample for any type of determination.  The CT work up report for this patient also noted a left thyroid nodule.

I'm not aware of any recent results in regards to the identification of the nodule, but this is something that I will be following up for my own education.  This may be a potential occurrence of an incidental finding for thyroid carcinoma.... who knows?

Ewing's Sarcoma

Sorry about the long hiatus, but here is something that came up a couple of weeks ago which was a bit tragic for the patient, but at the same time quite an interesting case.

I personally have not seen a gallium whole body scan like this, and likewise with the other technologists in the department.  This patient was being worked up for Ewing's sarcoma.  

When the patient arrived in our department, they were in a considerable amount of pain.  We limited the SPECT/CT to only 1 bed as oppose to our regular whole body SPECT/CT which covers 2 to 3 bed positions on our Symbia T6.  Having said that, it was quite obvious where the tumour was located.

Fig. 1  Ga-67 whole body image of a patient being worked up for Ewing's sarcoma.  The right  thoracic area has intense gallium uptake.

The right thorax contained majority of the gallium uptake, with little evidence of metastases outside of the area.  However, the CT demonstrated a much clearer extent of the disease involvement with the spine and the surrounding bony structures.  The patient originally was asymptomatic, but as the disease started to spread, a rapid loss in weight occurred and discomfort emerged from the right posterior region of the back.

Fig. 2  Transaxial CT slice.  Notice the periosteal reaction in the posterior rib and spine.

Fig. 3  Sagittal slice with an almost complete opacification of the right lung.  Most of the lung has collapsed due to the right sided mass and effusion.

Fig. 4  A coronal slice further depicting the multiple lytic changes in the right sided ribs as well as the invasion of the tumour into the spinal canal.

Overall the disease state was quite extensive with an extra large parenchymal mass filling up much of the right hemithorax, measuring up to 13 cm in thickness.  The disease may have started in the spine or in one of the ribs and over time became invasive.  A further MRI of the spine was performed to assess the spinal canal and spinal cord as the patient began to have bilateral leg weakness and tingling in the feet.

Generally with Ewing's sarcoma it often occurs during childhood and can start anywhere in the body.  However it tends to target the long bones, that are hard, dense bones that provide strength, structure, and mobility.  Almost a third of the patients have some metastases to other locations, generally to the lungs and in to other bones.  Click on the above link (Ewing's sarcoma) for more information.

Liver Spleen Scan Using Denatured Red Blood Cells

Denatured red blood cell scans are few and far between, but when something like this comes along, it piques everyone's interest. 

With this case here, the ordering physician was inquiring about the multiple intra abdominal deposits and had asked whether these deposits were related to splenules, caused by some kind of splenosis.  We are uncertain about the patient history since the technologist performing the scan did not inquire about the previous history of trauma or any iatrogenic events that may have potentially caused the spleen to rupture.  Previous ultrasounds or CT imaging were not performed at our facility and the patient did not bring any CD's with previous imaging from outside sources.  But thinking back, this patient must have some form of imaging done or otherwise, how did the physician know of the abdominal deposits?  At any rate this is what we got with respect to the imaging.  

After the initial reinjection of the denatured cells, a flow and blood pool images were acquired.  The delayed imaging was performed 20 minutes post injection, using a 2 bed SPECT/CT protocol.

Fig. 1 Anterior blood pool, after the denatured red blood cell injection.

Fig. 2 Posterior blood pool acquisition.

Fig. 3  Coronal slice.  Multiple foci of activity.  Note the activity over the dome of the liver and the perihepatic regions.

Fig. 4  Multiple uptake within the peritoneal cavity.

The MIP display above might not seem like very much, but there are multiple foci of tracer uptake scattered throughout the peritoneal cavity and the perihepatic region.  The largest and the most intense nodules occur in the splenic fossa along with multiple nodules tracking along the colon.

Fig. 5  SPECT/CT acquisition was performed to localize the denatured red blood cell uptake.

There is also focal activity in nodules adjacent to the liver as well as further nodules in the lateral right hepatic border and in the hepatorenal space.  Overall a lot of diffuse uptake can be observed, which is highly suggestive of splenosis.

We have a GMP approved radiopharmacy and all of the blood work is performed on site.  I must admit in the past, sometimes the labeling worked and sometimes it did not, however we have tweaked the procedure a little bit, and the information below is how we label and denature our red blood cells to ensure a quality scan.

Preparation of Radiolabeled Red Blood Cells Using the UltraTag In Vitro Method:

      Purpose:

The aim of this document is to provide information on the preparation and quality control of ^99mTc-labeled red blood cells using the UltraTag® in vitro method.

     Responsibilities:

It is the responsibility of the radiopharmacy technician to perform this procedure under strict aseptic conditions and as outlined in this protocol.

It is the responsibility of the radiopharmacist or the quality control technician to ensure that the correct RBC preparation procedure is followed and the final product meets the required specifications.

    Materials:

- lead glass syringe holder (3 mL size)

- syringe lead pig

- vial lead pig

- sterile 15 mL plastic centrifuge tubes

- sterile 18 or  21 gauge needles

- sterile 5 mL and 3 mL syringes

- sterile saline 0.9 % for injection USP

- UltraTag® kit

- ^99mTc sodium pertechnetate (370 – 1000 MBq)

    Procedure:

4.1.  Area setup:

·       Turn on laminar flow hood and wipe down surface of the hood with 70% isopropyl alcohol and a clean Kendall wipe. Spray and wipe with 70% IPA the materials needed to be placed in the hood.

·       Don hair cover, face mask, gloves and gown.

·       Turn on water bath and set the temperature at 50^oC, if preparing denatured RBC.

4.2.  Precautions:

·       During the labeling procedure, blood and blood components of the patient, who could potentially be infected with pathogens, need to be handled. To prevent contamination of the operator, double-gloving using waterproof gloves is recommended.

·       Since the cells have to be reinjected into the patient, strict aseptic conditions are required for the labeling procedure.

·       Simultaneous labeling of blood products from multiple patients is discouraged in order to prevent possible cross-contamination. At all times correct identification of the patient’s blood products should be guaranteed.

·       During the labeling care should be taken not to damage the cells, as this would result in leakage of the radioactivity from the cells, increased lung uptake and increased liver uptake.

4.3.  Radiolabeling of RBC with ^99mTc:

Note: The UltraTag® kit has 3 components:

a)     10 mL reaction vial containing stannous chloride, dihydrate (SnCl2•2H2O) 50 µg, minimum, stannous chloride, dihydrate (SnCl2•2H2O) 96 µg, theoretical, tin chloride (stannous, stannic) dihydrate, as stannous chloride, maximum dihydrate 105 µg, 3.67 mg sodium citrate dihydrate and 5.50 mg anhydrous dextrose.

b)     Syringe I: 0.6 mL contains 0.6 mg sodium hypochlorite (NaOCl). Protect from light.

c)   Syringe II: 1 mL contains 8.7 mg citric acid monohydrate, 32.5 mg sodium citrate dihydrate and 12.0 mg anhydrous dextrose.

4.3.1.     Collect patient's blood sample (1 - 3 mL) using heparin or ACD as an anticoagulant. The amount of ACD should not exceed 0.15 mL of ACD per mL of blood. The recommended amount of heparin is 10-15 units per mL of blood. DO NOT USE EDTA OR OXALATE AS AN ANTICOAGULANT.

4.3.2.     Using a large-bore needle (19 to 21 gauge), transfer 1.0 to 3.0 mL of anticoagulated whole blood to the reaction vial and gently mix to dissolve the lyophilized material. Allow to react for 5 min at room temperature.

4.3.3.     Add contents of Syringe I, mix by gently inverting four to five times.

4.3.4.     Add the contents of Syringe II to the reaction vial. Mix by gently inverting four to five times.

4.3.5.     Place the vial in a lead shield fitted with a lead cap. Add 370 to 925 MBq (10 to 25 mCi) sodium pertechnetate Tc-99m (in a volume of up to 3 mL) to the reaction vial. Use fresh generator eluate to avoid in-growth of ⁹⁹Tc.

4.3.6.     Mix by gently inverting reaction vial four to five times. Allow to react for 20 minutes with occasional mixing.

4.3.7.     Take a sample to assay labeling efficiency immediately prior to injection (see 4.4.2).

If LE > 90%, proceed to step 4.3.8 for denatured RBC or step 4.3.9. for normal RBC.

4.3.8.     Heat the tagged cells in a water bath with a little agitation at 49 - 50^oC for no more than 15 min. Proceed to step 4.3.9.

4.3.9.     Mix gently prior to withdrawal of patient dose. Aseptically transfer the ^99mTc-labeled red blood cells to a syringe for administration to the patient. Use a large bore needle to prevent hemolysis.

4.3.10.  Assay for radioactivity. Prepare labels and paper work using Pinestar.

4.3.11.  ^99mTc-labeled red blood cells should be injected within 30 minutes of preparation or as soon as possible thereafter.

4.3.12.  Clean up the laminar flow hood. Place radioactive waste in the waste disposal bin in the hot lab and non-radioactive sharps waste and blood/plasma in the sharps waste container. Remove the equipment from the laminar flow hood and wipe the surface down with 70% isopropyl alcohol using a lint-free cloth.

4.4. Quality control:

4.4.1.     Visual inspection (performed routinely):

·         At the end of the procedure and before collecting the radiolabeled RBC in the syringe for patient administration, a visual inspection for clumps, clots and aggregates should be performed by gently rotating the tube.

·         In case of aggregates, they should be dissolved by gently shaking or pipetting the sample.

·         If clumps cannot be dissolved, the preparation should not be injected.

4.4.2.     Labeling efficiency (LE) (performed routinely):

·       Transfer 0.2 mL of the ^99mTc-labeled RBC to a 15 mL centrifuge tube containing 2 mL of 0.9% NaCl. Centrifuge for five minutes and carefully pipet off the diluted plasma. Measure the radioactivity in the plasma and red blood cells separately in a dose calibrator. Calculate labeling efficiency as follows:

% LE = (Activity RBC x 100)/(Activity RBC + Activity Plasma)

·         LE = 90 - 98 %

·         If LE < 90 %, further quality control should be performed, such as microscopic inspection and test for cell viability (see 4.4.3).

4.4.3.     Trypan blue exclusion test for cell viability (recommended periodically):

·       Take a small sample (0.2 mL) from the radiolabeled RBC and dilute it with 1 ml of saline for injection.

·         In a small tube mix 50 ul 0.4 % trypan blue solution and 50 ul of the radiolabeled RBC sample.

·         Put a drop of this mixture in a hemocytometer and place it under the microscope.

·         Check for clumps and microaggregates of cells.

·         Calculate the percentage of blue stained cells from the total cell number. This is the percentage of damaged cells.

·         If a preparation has > 10 % blue-stained cells, it should not be released for injection into the patient.

4.4.4.     Sterility (recommended periodically):

Sterility of the final preparation should be tested periodically, especially in case of any modification to the procedure.

So there you have it.

NB:  Someone had mentioned that I forgot to add steps 5.3.8, 5.4.2, 5.4.3. Everything is contained within the blog.  I just mislabeled the numbered steps.  The "5" should have been a "4" in the body of the blog.  Apologies, it has been corrected..