Interventional Radiology Treatment of Liver Lesions
Review of high yield interventional radiology and nuclear medicine concepts regarding treatment of liver lesions for radiology board examination review.
Show Notes/Study Guide:
What options do IR doctors have to treat liver masses?
Y90: Use trans-arterial instillation of Y90 particles to embolize and radiate an HCC.
Trans-arterial chemoembolization (TACE): for palliative HCC therapy, has iodized oil that appears dense on CT
Radiofrequency ablation (RFA): Use RF coils to head tissue to cause cellular damage of tumor cells. This can be performed percutaneously unlike TACE or Y90.
Cryoablation is another possible option.
What factors should you consider when deciding between Y90, TACE, or RFA for treatment of malignancy in the liver?
If there is 1 tumor under 5 cm or 3 or fewer tumors under 5 cm in size, you can consider percutaneous RFA. If HCC is larger than 5 cm and/or you have more than 3 tumors, you can do Y90 or TACE. Also, large lesions (about 3 cm or greater in size) may need a combination of therapy such as RFA and TACE.
What preparation is required to plan for a Y90 treatment?
First is a planning angiogram to assess anatomy and perform Tc99 MAA lung shunt fraction needs to be determined prior to Y90 treatment. Also, prior to treatment the gastroduodenal artery (GDA) and/or the right gastric artery (a branch of the left hepatic artery) may be embolized to prevent formation of non-healing gastric ulcers.
The Milan criteria is used for what? What are the Milan criteria rules?
Milan criteria is used for evaluation of liver transplantation candidacy in the setting of HCC. According to the Milan criteria you can be considered for liver transplantation if you have 1 HCC under 5 cm in size or up to 3 HCCs under 3 cm in size. You are not allowed to have any extrahepatic disease to be considered for liver transplantation.
What material is best for shielding Y90 particles?
For Y90 plastic or glass shielding is necessary as shielding with lead or tungsten will cause bremsstrahlung from interaction with high energy beta particles and formation of x-rays.
True or false? the beta radiation from Y90 can penetrate outside of the patient’s body.
False. The beta radiation cannot pass through the patient’s body. However, the bremsstrahlung x-rays from Y90 (that are used to create nuclear medicine images) can penetrate the patient body and cause exposure to others. But the beta particles themselves travel only a short distance in the body (about 5 mm which equals a few hundred cell distance) before they deposit their energy—thereby killing cells adjacent to where they are located.
What is the classic indication for Y90 therapy in the liver?
Y90 is classically indicated for locoregional palliative treatment of unresectable malignancy in the liver. The goal of therapy can be to obtain local control of disease, to bridge to transplant or make the patient an improved candidate for other interventions. Y90 is classically not used for curative intent historically but this is now questionable.
Fill in the blanks: Normal hepatic parenchyma derives most of its blood supply from _____ and hepatic malignancies typically derive most of their blood supply from ______.
Normal liver parenchyma derives most blood supply from the portal vein whereas hepatic malignancies most commonly derive blood supply from the hepatic artery. Hence trans-arterial treatments of liver tumors as this preferentially deposits more therapeutic/radioactive agents in areas of malignancy versus normal hepatic parenchyma. Y90 agents are injected intra-arterially selectively to the hepatic artery and then embolize in tissue capillaries where they get stuck and radiate the surrounding tissue (preferentially areas of metastatic disease given the hepatic arterial supply that is greater to metastases in the liver compared to normal liver parenchyma).
Tips: if portal vein thrombosis is present you need to be cautious in your approach, so you don’t cause significant liver infarction.
Name some common contraindications to Y90 therapy.
Marked liver failure (look for very abnormal LFTs, abdominal ascites, clinical signs of liver failure in a question stem), lung shunt fraction that exceeds 20%, diffuse hepatic malignancy, contrast contraindication precluding angiography.
True or false? a pre-treatment planning Tc99-MAA planning study is required for Y90 therapy.
True.
What is the purpose of the pre-treatment MAA study prior to Y90 therapy?
To evaluate, after intra-hepatic arterial MAA injection, for significant shunt fraction to the lungs, verify that there is desired uptake in the liver lesions (therefore Y90 would be delivered successfully) and no abnormal/unexpected uptake elsewhere (such as other solid organs, the stomach, etc.). Pre-treatment MAA study can be used to identify need for pre-Y90 coil embolization procedures to try to lower shunting from hepatic artery to areas like lung, gut, stomach and then the MAA study procedure may be performed after the coiling procedure to document and ensure that shunting is now minimized and within acceptable ranges to proceed with Y90 therapy.
What are some basic differences between TheraSpheres™ and SIR-Spheres™?
Materials: TheraSpheres™ use glass beads whereas SIR-Spheres™ use resin beads. TheraSpheres™ are FDA approved for unresectable HCC and SIR-Spheres™ are FDA approved for colon cancer metastases to the liver. TheraSpheres™ have much higher activity per bead than SIR-Spheres™ so you can inject fewer particles with TheraSpheres™ to deliver the same dose of radioactivity.
Which artery is commonly coiled prior to Y90 therapy to prevent delivery of particles to the stomach?
Gastroduodenal artery (GDA)
What is the upper limit for lung shunt fraction on a pre-Y90 therapy MAA study above which Y90 therapy typically may not be considered?
A lung shunt fraction over 20% is typically a contraindication to Y90 therapy. The goal is to prevent severe radiation pneumonitis. Shunt fractions approaching 20% may indicate dose reduction or performing pre-therapy embolization to minimize collaterals to the lungs.
True or false? For board exams lesions in the left and right lobes of the liver may be treated at the same timepoint with Y90.
Generally false. To prevent liver failure, you only treat one lobe at a time, separated by about 4 weeks to allow liver recovery/assessment of response prior to treating the other lobe of the liver.
Does the common hepatic artery most commonly arise from the celiac axis or the superior mesenteric artery?
The common hepatic artery is most commonly a branch of the celiac axis. Know what conventional celiac axis anatomy looks like and be able to identify the major branch vessels for the Core Exam.
On a Y90 pre-therapy planning angiogram why might you evaluate the superior mesenteric artery anatomy?
Prior to Y90 therapy you should evaluate the superior mesenteric artery anatomy to evaluate for and exclude a replaced or accessory hepatic artery that arises from the SMA. This is important to identify prior to Y90 therapy to prevent non-target embolization and to deliver the Y90 to hepatic lesions through the most appropriate feeding arterial vessels.
MAA particle size is approximately how big?
I've covered this before, but MAA particles are approximately 10-100 micrometers in size. This is large enough for particles to get wedged in small capillaries but not large enough to cause significant arterial embolization of larger arteries/branches.
What variables are considered for Y90 dose calculation?
Dose calculation formulas for Y90 are something that I didn't memorize for the ABR Core Exam, but I think it is important to know what factors influence the dose calculation. These are the desired dose to the target, the mass of the liver which can be calculated from 3D volume rendering, the lung shunt fraction, and the anticipated residual waste.
