Therasphere Part Deux

Our first patient, who has a long standing history of hepatocellular carcinoma (HCC), was excluded as a surgical candidate to remove the tumour in the right lobe of the liver because the patient suffers from portal hypertension and low platelets.  The alternative consideration was for transcatheter arterial chemoembolization (TACE) to treat the tumour,  however somehow this patient ended up in the trial study of Yittrium-90 Theraspheres at our facility (click on link for further reading)

A mesenteric angiography and embolization was performed as the first step of the selective internal radiation therapy.  The reasoning is to ensure the blood flow localizes into the tumour site while sparing normal healthy sites when the Y-90 is delivered.   The mircocatheters where inserted through the right femoral artery and threaded to the right hepatic and left hepatic arteries for the arteriography.  The right gastric artery, which arose from proximal left hepatic artery, was embolized with vortex coils.  Furthermore the gastroduodenal artery was emoblized as well, leaving patent the common hepatic artery, the left and right hepatic arteries.

Fig. 1  Infusion of contrast through the right hepatic artery.  Note the embolization coils below.

Fig. 2  Infusion of contrast through the right hepatic artery, outlining the tumour in the right lobe.

Fig. 3  The right lobe tumour is now fully visualized, with limited shunting.  However there is still extraneous vascularity.  Thus the lung shut fraction is calculated to quantitate the amount.

After the embolization process, Tc-99m MAA was injected through the microcatheter for the lung shunt study.  After the injection, the patient was stabilzed for transport to Nuclear Medicine, and the following images were taken.

Fig. 4  Anterior and posterior images were taken to determine any major shunting of blood to the lungs or stomach.

Fig.  5  Regions of interest were drawn over the lungs and liver and a geometric mean was calculated to determine the lung shunt fraction (LSF).

Lung shunt fraction was calculated to be 3.0%.  There is no cut off with regards to the LSF value to be excluded from the treatment.  However it is the discretion of the interventional radiologist who will be administering the Y-90 to determine the patient's inclusion within the treatment study.

Two weeks after the initial angiography and embolization, the Y-90 theraspheres were adminstered.  Based on the size and volume of the tumour which the interventional radiologist calculated prior to the administration, we wanted to give approximately 2.5Gbq of Y-90 to deliver 120Gy to the tumour site.

Nordion which supplies the theraspheres, has an excel worksheet to help with the ordering of the Y-90 dose to ensure the proper calibration of the actual dose.
In the end, the amount that we calculated (approximation) of the dose delivered to the tumour site was about 2.49GBq, based on a 1.7% residual activity remaining in the Y-90 administration vial.  Overall the tumour received 120.7Gy with the lungs receiving approximately 3.73Gy, based on the LSF value.

Having worked through our first patient it is important to address the fact that most Nuclear Medicine technologists are accustomed to working with radioactive materials.  However the interventional radiology (IR) technologists and some IR doctors do not.  The dose rate is quite high with respect to the Y-90 vial.... but we normally do not tell them how high it really is.  Thus it is a good idea that you get them on board with respect to working with radioactive materials and how to handle these materials without causing too much of a mess.  The reason why, is that they are most likely going to set up the Y-90 administration set, since they have much more experience than Nuclear Medicine technologists in a sterile field.  Plus it will be the IR doctors (at least at our site), that will be injecting the Y-90.

Fig. 6  An unassembled administration set.  Everything is performed in a sterile field.  I will endeavour to update this image, once everything is connected together, when our next patient arrives.  Which should be in 2 weeks time.

Theraspheres

Just got back from Chicago... (fun town), on a training seminar in regards to TheraSpheres.  For those in the United States and Europe, this might be routine practise in treating liver cancers (hepatocellular carcinoma HCC), but not so much here in Canada.  There are only a few places in Canada that are performing these procedures (BC, Alberta) but not sure what type of volumes they have in regards to this type of treatment.  The Nordion sales reps have stated that they have some type of involvement within these regions.

At any rate what is a TheraSphere?  They are glass beads with Yittrium-90 attached to the surface.  The beads themselves are biocompatible and insoluble and have a mean size between 20 - 30um.  These beads are injected through a femoral line while undergoing a hepatic angiogram in Interventional Radiology (IR) and the beads are deposited close to the site of the liver lesion that you want to treat.

What's tricky about this is, figuring out the blood supply to the region of the liver in and around the tumour site(s).  For the most part the blood flow to the liver is fairly predictable, but with respect to some patients it's a bit more complicated because of a variety of arterial variants, parasitization of flow, accessory arteries, retrograde blood flow etc. that if not found with a thorough investigation, the deposition of the TheraSpheres will not go entirely to the tumour, but elsewhere within the body.  This is not a good thing, since adverse reactions may potentially occur.  The case studies illustrated these quite well at the training seminar.  However, for the most part Yittrium-90 radioembolization of the HCC tumours has several advantages in that it has a lower toxicity profile in comparison to transarterial chemoembolization.

So what does TheraSpheres have to do with Nuclear Medicine?  Well for the most part we assay and deliver the Yittrium-90 to the angiography suite, and from there the IR techs and the IR doctors take care of the rest with respect to the injection and the clean up.  This will vary from site to site, depending upon the level of comfort and training in dealing with radioactive materials.

However even before this occurs, Nuclear Medicine is important in determining extra hepatic shunting to the lungs or gastrointestinal tract as part of the selection process in figuring out who are good candidates for this treatment.

150MBq of Tc-99m MAA is injected with a microcatheter into the hepatic artery after coil embolization of all visible non hepatic arterial flow.  Basically, whatever blood flow that doesn't deal with the liver, they get clamped down with coils, in order to figure extrahepatic flow.  The image below is an example of this type of imaging.

Fig. 1  ROI's drawn over the lungs and liver to determine the counts for geometric calculations to determine the Lung Shunt Function (LSF)

Anterior and posterior images are taken to determine regions of interest (ROI) to find out the Lung Shunt Fraction (LSF).  The geometric means are calculated from the lungs and liver using the numbers from the ROI's  and are used in this equation:

LSF = Lungs / (Liver + Lungs) *100

The reason why this is important is because it helps in determining the dosimetry calculations for pre and post treatment.  This is important since you need to know how much radiation to give given a specific volume of liver that you plan to treat without affecting other parts of the body (ie. lungs).

There is the question of planar versus SPECT/CT imaging with MAA.  At the training seminar, planar imaging was described, but others have suggested performing SPECT/CT.  Since at our site we have limited experience with this protocol, we would need to speak to the IR doctors and the Nuc Med doctors to figure out what they want.

The current imaging protocol for Tc-99m MAA:

Static Imaging Protocol (Northwestern Hospital, Chicago):

Dosage:

- 37 -185 MBq Tc-99m MAA, injected in IR and the patient delivered to Nuclear Medicine

Equipment:

- Any large FOV dual detector gamma camera, with LEAP or LEHR collimation

Imaging:

Option 1:  The patient is positioned supine under the gamma camera and 4 images are acquired.  Anterior and posterior images of the abdomen and of the thorax are acquired separately

Option 2:  The patient is positioned supine under the gamma camera and a whole body scan is acquired

Camera Parameters:

- Acquisition matrix = 256 X 256

- Zoom = 1.45 or less to ensure all activity visible in FOV; total counts >1M

- Counting time - 5mins per 74 MBq administration of Tc-99m

SPECT/CT Imaging Protocol (University Hospital Essen, Essen)

Dosage:

150 MBq Tc-99m MAA

Equipment:

- Dual headed gamma camera, with SPECT/CT capability

Imaging:

- 30 minutes post injection of Tc-99m MAA, anterior and posterior planar images of the whole body 

- SPECT/CT afterwards

Camera Parameters:

- SPECT - 128 X 128 matrix

- 128 frames (25 secs/frame)

- CT - 130 keV, 17 mAs, 5mm slices

There is also talk about PET/CT imaging as well.  Since Yittrium-90 is a beta emitter, having the patient come back the following day after treatment allows imaging of the distribution and deposition of the microspheres within the body.  

Anyway, there is a lot to know about this procedure and I am only scratching the surface. At our facility we have had some experience with this many years ago, but now there is a real push with some of the doctors at the hospital to revisit this type of treatment again.

Stay tuned........

Update:  Check out Theraspheres Part Deux, in this blog site.  We've performed out first LSF and treatment.

Collateral Blood Flow

What the .....?"  Yup, that's what the tech said after the injection of MAA into the left arm, after the initial ventilation scan.

Indication:  Rule out any significant pulmonary hypertension.  Pre-op assessment.

Findings:  Preliminary flow study demonstrates extensive collateralization of the left chest wall.  Matched and unmatched perfusion defects in both lungs.  Impression, low probability for pulmonary embolism.  Possible left subclavian obstruction.

Hx:  Pulmonary hypertension is not one of the indications for a VQ scan, unless they have had a chronic history of a pulmonary embolism (PE).  The thoracic surgeon ordered this test to ensure that there were no complications before they performed an open biopsy on the left lung.  The patient had previous non Hodgkin's lymphoma, was experiencing SOB, reduced lung capactiy from the PFT study, developed hemoptysis, fever and chills.  Based on the CT and a failed FNA, the open biopsy would help to figure out if there was a relapse in the lymphoma or lung fibrosis or some other inflammatory disease.