Yttrium

Dosage for Yttrium-90 is not calculated in milligrams, but in Gigabecquerels (GBq) or Millicuries (mCi), which measure radioactive activity.

• For Liver Cancer (SIRT): The dose is highly individualized. Healthcare providers use the 'Body Surface Area (BSA) model' or the 'Partition model' to calculate the required activity. A typical dose range may be between 1.0 GBq and 3.0 GBq, depending on the volume of the tumor and the health of the surrounding liver tissue.
• For Non-Hodgkin Lymphoma (Zevalin): The standard dose is 0.4 mCi/kg (14.8 MBq/kg) for patients with normal platelet counts, up to a maximum of 32 mCi.

Yttrium-90 is not routinely approved for pediatric use. However, in specialized oncology centers, it may be used off-label for pediatric liver tumors (hepatoblastoma). Dosing in these cases is strictly determined by pediatric interventional radiologists based on tumor volume and shunting studies. Safety and efficacy have not been formally established in patients under 18 years of age by the FDA.

Renal Impairment

For microsphere therapy, renal impairment does not typically require a dose adjustment because the Yttrium is not excreted by the kidneys. However, for systemic Yttrium-90 (Zevalin), caution is advised as the chelate may have altered clearance in patients with severe kidney disease.

Hepatic Impairment

This is a critical area for Yttrium SIRT. Patients with a bilirubin level >2.0 mg/dL may be at higher risk for radiation-induced liver disease (RILD). Healthcare providers may reduce the dose or withhold treatment if liver function is severely compromised (Child-Pugh Class C).

Elderly Patients

Clinical trials have shown that patients over 65 respond similarly to younger patients. However, because elderly patients are more likely to have reduced hepatic reserve, healthcare providers often monitor liver function more frequently post-procedure.

Yttrium is never self-administered. It is a complex procedure performed in a hospital setting:

1. 1Pre-procedure Mapping: One to two weeks before the Yttrium dose, a 'dummy run' with a tracer (Tc-99m MAA) is performed to ensure the spheres won't travel to the lungs.
2. 2The Procedure: An interventional radiologist inserts a catheter into the femoral artery (groin) and threads it into the hepatic artery. The Yttrium microspheres are then slowly infused.
3. 3Post-Procedure: Patients are monitored for several hours. Because Y-90 is a beta emitter with low external penetration, strict 'radiation isolation' is usually not required, but close contact with children or pregnant women should be avoided for 3-7 days.

Because Yttrium is a scheduled hospital procedure, a 'missed dose' involves a missed appointment. If the procedure is delayed, the radiopharmaceutical must often be re-ordered because the isotope decays quickly (half-life of 64 hours). If you miss your appointment, contact your oncology team immediately to reschedule and manage the logistics of the radioactive material.

An overdose of Yttrium radiation can lead to severe radiation-induced liver disease (RILD) or 'Post-Radioembolization Syndrome.' Symptoms include severe abdominal pain, rapid liver failure, or fluid in the abdomen (ascites). Treatment is supportive, focusing on managing liver inflammation and maintaining fluid balance. Emergency measures include the administration of corticosteroids to reduce radiation-induced swelling.

> Important: Follow your healthcare provider's dosing instructions and pre-procedure guidelines exactly. Do not attempt to adjust your treatment schedule without medical guidance.

Most patients receiving Yttrium-90 microspheres experience Post-Radioembolization Syndrome (PRS). This is a cluster of symptoms caused by the localized radiation and the embolization of the tumor's blood supply.

• Fatigue: This is the most common symptom, often described as a profound sense of tiredness that can last for 2 to 4 weeks after the procedure.
• Abdominal Pain: A dull ache or pressure in the upper right quadrant of the abdomen, usually manageable with over-the-counter or mild prescription pain relievers.
• Nausea and Vomiting: Typically occurs in the first 24-48 hours. Healthcare providers usually prescribe anti-nausea medication (antiemetics) before the procedure.
• Low-Grade Fever: A mild elevation in temperature as the body responds to the dying tumor cells.
• Loss of Appetite (Anorexia): Temporary changes in taste or desire to eat, which usually resolve within 10 days.

• Mild Liver Function Abnormalities: Temporary elevations in AST, ALT, or bilirubin levels seen on blood tests.
• Leukopenia/Thrombocytopenia: A drop in white blood cell or platelet counts, more common when Yttrium is used for lymphoma (Zevalin) than for liver cancer.
• Diarrhea: Often transient and related to the body's inflammatory response.

• Radiation Pneumonitis: Inflammation of the lungs if the Yttrium microspheres 'shunt' or leak from the liver to the lungs. This causes shortness of breath and a dry cough.
• Radiation-Induced Gastritis: If microspheres accidentally travel to the stomach or duodenum, they can cause severe ulcers that are difficult to heal.
• Cholecystitis: Inflammation of the gallbladder if the Yttrium is accidentally delivered to the cystic artery.

> Warning: Stop following your normal routine and call your doctor immediately or seek emergency care if you experience any of these:

• Severe Abdominal Pain: Especially if it is sharp or worsening, which could indicate a gastric ulcer or gallbladder perforation.
• Jaundice: Yellowing of the eyes or skin, indicating acute liver failure or Radiation-Induced Liver Disease (RILD).
• Difficulty Breathing: A possible sign of radiation pneumonitis (lung injury).
• Persistent Vomiting: Inability to keep fluids down, leading to dehydration.
• Signs of Infection: High fever (over 101°F), chills, or severe shaking.

• Radioembolization-Induced Liver Disease (REILD): A form of delayed liver injury that can appear 1 to 6 months after treatment. It is characterized by ascites (fluid in the belly) and jaundice.
• Portal Hypertension: Increased pressure in the veins of the liver, which can lead to spleen enlargement or esophageal varices (swollen veins in the throat).
• Secondary Malignancies: As with all radiation, there is a theoretical long-term risk of developing a new cancer, though this is rare in the context of treating an existing advanced malignancy.

For Ibritumomab tiuxetan (Yttrium-90 Zevalin), the FDA has issued a Black Box Warning regarding:

• Serious Infusion Reactions: Some patients may experience severe allergic reactions during the infusion.
• Prolonged and Severe Cytopenias: Drastic drops in blood counts that can last for weeks, increasing the risk of hemorrhage or fatal infection.
• Severe Cutaneous Reactions: Rare but fatal skin reactions (like Stevens-Johnson Syndrome) have been reported.

Report any unusual symptoms to your healthcare provider immediately. Early intervention is key to managing Yttrium-related complications.

Yttrium-90 is a radioactive material. While the radiation it emits (beta particles) has a short range, patients must follow specific safety protocols to protect others. For the first 3-7 days after a Yttrium procedure, you should avoid prolonged close contact (closer than 3 feet) with pregnant women or children. Always wash your hands thoroughly after using the bathroom, as trace amounts of radiation may be present in bodily fluids.

As noted in the side effects section, Yttrium-labeled Zevalin carries Black Box Warnings for Severe Infusion Reactions, Severe Cytopenias (blood cell loss), and Severe Mucocutaneous Reactions. There are currently no Black Box Warnings for Yttrium microspheres (TheraSphere/SIR-Spheres), though they are restricted to specialized medical facilities.

• Lung Shunting: Before receiving Yttrium, a Tc-99m MAA scan must be performed. If the scan shows that more than 20% of the spheres would travel to the lungs (a 'shunt'), the Yttrium procedure cannot be performed due to the risk of fatal lung inflammation.
• Gastrointestinal Reflux: The interventional radiologist must ensure that the Yttrium does not flow backward into the arteries supplying the stomach or intestines. This can cause severe, non-healing radiation ulcers.
• Liver Reserve: Patients with very poor liver function (Child-Pugh Class C) are at high risk for total liver failure after Yttrium treatment.

Following Yttrium therapy, patients require rigorous monitoring:

• Liver Function Tests (LFTs): Bilirubin, Albumin, AST, and ALT should be checked every 2 weeks for the first 3 months.
• Complete Blood Count (CBC): To monitor for drops in white blood cells or platelets.
• Imaging: A CT or MRI scan is typically performed 4 to 8 weeks after the procedure to evaluate the tumor's response to the radiation.

You should not drive yourself home after a Yttrium procedure due to the sedation used during the catheterization. In the days following, fatigue is common. Do not operate heavy machinery if you feel excessively tired or are taking prescription pain medications (opioids) for abdominal discomfort.

Alcohol should be strictly avoided for at least several weeks following Yttrium therapy. The liver is already under significant stress from the radiation and the dying tumor; alcohol can increase the risk of Radiation-Induced Liver Disease (RILD) and permanent scarring (cirrhosis).

Yttrium microsphere therapy is a one-time or few-time procedure, not a daily medication. There is no 'withdrawal' syndrome. However, if you are scheduled for multiple sessions (e.g., treating the right lobe then the left lobe), the second session may be canceled if your liver function does not recover sufficiently from the first dose.

> Important: Discuss all your medical conditions, especially any history of lung disease or stomach ulcers, with your healthcare provider before starting Yttrium.

• Live Vaccines: Because Yttrium (especially Zevalin) can suppress the immune system, live vaccines (e.g., MMR, Yellow Fever) should not be administered. The vaccine virus could replicate uncontrollably, leading to severe infection.
• Concurrent External Beam Radiation: If a patient is already receiving high-dose external radiation to the liver, Yttrium-90 SIRT is generally contraindicated as the cumulative radiation dose would likely cause total liver necrosis.

• Sorafenib (Nexavar): Many liver cancer patients take this oral chemotherapy. Some studies suggest that taking Sorafenib too close to Yttrium therapy can increase the risk of liver toxicity. Most protocols recommend stopping Sorafenib 1-2 weeks before and after the Yttrium procedure.
• Hepatotoxic Drugs: Medications known to stress the liver (e.g., high-dose acetaminophen, certain anti-fungals like ketoconazole) should be used with extreme caution during the 3 months following Yttrium therapy.

• Anticoagulants (Warfarin, Eliquis): Because the Yttrium procedure involves an arterial puncture, blood thinners must be stopped several days prior to prevent severe bleeding at the catheter site.
• Corticosteroids: While often used to treat side effects, long-term use can mask signs of infection that might occur if Yttrium causes low white blood cell counts.

• Alcohol: As mentioned, alcohol increases liver stress and should be avoided.
• Grapefruit Juice: While not a direct interaction with Yttrium itself, grapefruit juice inhibits CYP3A4 enzymes. If you are taking other chemotherapies or pain medications alongside Yttrium, grapefruit could dangerously increase their levels in your blood.

• St. John's Wort: This herbal supplement can induce liver enzymes, potentially altering the metabolism of other drugs you are taking to manage your cancer.
• Milk Thistle: Often taken for 'liver health,' milk thistle can interfere with certain metabolic pathways. Patients should consult their oncologist before taking any herbal supplements during radiation therapy.

• Tumor Markers (AFP, CEA): These markers may temporarily spike immediately after Yttrium treatment as the dying tumor cells release proteins into the bloodstream. This does not necessarily mean the cancer is growing.
• Thyroid Scans: If Yttrium is present in the body, it may interfere with other nuclear medicine scans for several days due to background radiation.

For each major interaction, the mechanism usually involves additive toxicity (two things hurting the liver at once) or pharmacodynamic interference (competing for the body's recovery resources).

> Important: Tell your doctor about ALL medications, supplements, and herbal products you are taking, including those for blood pressure, diabetes, or pain.

Conditions where Yttrium must NEVER be used include:

• Pregnancy: Yttrium-90 is highly teratogenic. Radiation exposure to a fetus can cause severe birth defects, miscarriage, or fetal death.
• Excessive Lung Shunting: If the pre-treatment scan shows that a significant amount of the dose (>20%) would reach the lungs, the procedure is strictly forbidden due to the risk of fatal radiation pneumonitis.
• Severe Hepatic Failure: Patients with 'liver failure' (e.g., Child-Pugh Class C, bilirubin >3 mg/dL) cannot tolerate the additional stress of radiation.
• Gastrointestinal Reflux: If the arterial anatomy is such that microspheres cannot be prevented from entering the stomach or bowel, the procedure must be aborted.

Conditions requiring careful risk-benefit analysis:

• Portal Vein Thrombosis: If the main vein to the liver is blocked, the liver is already struggling for blood. Adding Yttrium (which blocks the artery) can cause a total loss of blood flow to the liver.
• Prior Liver Radiation: Previous treatments increase the risk of the liver not being able to regenerate.
• Limited Pulmonary Reserve: Patients with severe COPD or lung fibrosis may not tolerate even a small amount of lung shunting.

• Glass or Resin Allergies: While extremely rare, some patients may have sensitivities to the materials used to create the microspheres.
• Murine (Mouse) Protein Allergy: For Yttrium-90 Zevalin, because the antibody is derived from mouse cells, patients with a known allergy to mouse proteins (HAMA) may have a severe allergic reaction.

> Important: Your healthcare provider will evaluate your complete medical history, including your 'shunting' scan and liver function tests, before prescribing Yttrium.

Yttrium-90 is classified as FDA Pregnancy Category X. This means that studies in animals or humans have demonstrated fetal abnormalities and the risk of the drug in pregnant women clearly outweighs any possible benefit. Women of childbearing age must have a negative pregnancy test before the procedure. Effective contraception must be used for at least 6 months following treatment. If a patient becomes pregnant while carrying Yttrium microspheres, they must be counseled on the high risk to the fetus.

It is unknown if Yttrium-90 is excreted in human milk. However, because of the potential for serious adverse reactions and radiation exposure to the nursing infant, breastfeeding is strictly contraindicated. For systemic Yttrium (Zevalin), breastfeeding should be discontinued permanently. For microspheres, it should be discontinued for at least 2 weeks or until the radiation has decayed significantly.

Yttrium is not FDA-approved for use in children. The long-term effects of internal radiation on a developing child's liver and bones are not well-studied. In rare cases of pediatric liver cancer, Yttrium may be used under 'compassionate use' protocols in major academic centers, with doses adjusted for the smaller liver volume.

Clinical data indicates that elderly patients (over 65) do not experience more side effects than younger patients. However, the 'liver reserve' (the ability of the liver to bounce back) is often lower in the elderly. Healthcare providers must be cautious with dosing in patients over 80 or those with significant 'polypharmacy' (taking many other medications).

Since Yttrium microspheres are not cleared by the kidneys, patients with mild to moderate renal impairment can usually undergo the procedure safely. However, those on dialysis require special coordination between the interventional radiologist and the nephrologist to ensure the catheterization procedure is timed correctly with their dialysis schedule.

This is the most critical special population. Dosing is often reduced by 25-50% for patients with moderate hepatic impairment (Child-Pugh Class B). Patients with Class C should generally not receive Yttrium. The goal is to treat the tumor without pushing the patient into 'end-stage' liver failure.

> Important: Special populations require individualized medical assessment and often a multidisciplinary board (Tumor Board) review.

Yttrium-90 is a pure beta-emitter. It decays by emitting a high-energy electron (beta particle) from its nucleus.

1. 1Cytotoxicity: The beta particles cause 'double-strand breaks' in the DNA of cells. This prevents the cancer cells from replicating and eventually kills them.
2. 2Crossfire Effect: Because the beta particles travel up to 11mm (mean 2.5mm), a single microsphere can kill cancer cells in a sphere of tissue around it, even if the sphere didn't land directly inside that specific cell.
3. 3Embolization: The physical presence of the microspheres (20-60 microns in diameter) blocks the small 'capillaries' feeding the tumor, starving it of oxygen (ischemia).

• Onset of Effect: The radiation begins working immediately upon implantation. However, because cells take time to die and be cleared by the body, the tumor may not shrink on a scan for 4 to 12 weeks.
• Duration: The radiation is active for approximately 10 to 14 days (about 4-5 half-lives). After 30 days, 99% of the radiation has been spent.
• Tolerance: Unlike chemotherapy, tumors do not usually develop 'resistance' to radiation, though the healthy liver's tolerance for radiation limits how many times the procedure can be repeated.

| Parameter | Value |

|---|---|

| Bioavailability | 100% (Directly implanted) |

| Protein Binding | N/A (Microspheres) / High (Zevalin) |

| Half-life (Physical) | 64.1 Hours |

| Mean Tissue Penetration | 2.5 mm |

| Maximum Tissue Penetration | 11 mm |

| Excretion | Minimal (Physical decay to Zirconium-90) |

• Molecular Formula: $^{90}Y$
• Molecular Weight: 89.907 g/mol
• Solubility: Insoluble (as glass/resin spheres); soluble as Yttrium Chloride ($YCl_3$).
• Structure: Yttrium is a silvery-metallic element. In medicine, it is usually produced in a nuclear reactor by bombarding Yttrium-89 with neutrons.

Yttrium-90 belongs to the class of Therapeutic Radiopharmaceuticals. Within the liver-directed therapy area, it is the primary agent for Selective Internal Radiation Therapy (SIRT). It is chemically related to other lanthanides and often grouped with 'Rare Earth' elements.