Nuclear: Therapy Flashcards
What radiopharmaceuticals have been approved for treating bone pain associated with metastatic disease from breast and prostate cancer?
- Strontium-89 chloride (Sr-89)
- Samarium-153 EDTMP (Sm-153)
- Radium-223 dichloride (Ra-223)
Can pts receive radiopharmaceuticals to treat bone pain while receiving external radiation treatment?
Yes, external radiation is not a contraindication
Absolute contraindications for Sm-153 EDTMP treatment of bone pain
- Pregnancy
- Breastfeeding
- Renal failure (GFR < 30)
Note: These are contraindications for bone pain treatment with either Sr-89 or Sm-153.
How does strontium-89 chloride (Metastron) work?
It complexes with the hydroxyapatite in areas of high bone turnover and is a pure beta emitter
Note: It has high bone marrow toxicity and isn’t used as much as the newer agents (Sm-153 and Ra-223).
Which is better for treating bone pain: Sr-89 or Sm-153 EDTMP?
Sm-153 EDTMP (less bone marrow toxicity and also emits gamma rays that can be used for imaging)
Note: “Samarium is a Good Samaritan”.
Side effects of Sm-153 EDTMP
Myelosuppression (mostly thrombocytopenia and leukopenia)
Note: This is transient and goes away faster than with Sr-89.
How does Samarium-153 EDTMP (Quadramet) work?
It complexes with the hydroxyapatite in areas of high bone turnover and is a beta and gamma emitter (allowing for imaging)
What is the mechanism of excretion of Sm-153?
Renal (primarily)
Note: This is why renal failure (GFR < 30) is an absolute contraindication.
What is the best radiopharmaceutical to use for bone pain?
Radium-223 (Xofigo)
Note: It has the least bone marrow toxicity (as an alpha emitter it has a shorter range of damage) and a long half life that makes shipping easy.
How does radium-223 work?
It behaves like calcium and gets absorbed into the bone matrix at sites of active bone mineralization, where it emits alpha particles
Side effects of radium-223 therapy
- Diarrhea
- Fatigue
- Nasea/vomiting
- Bone pain
Note: These are more significant than the minimal bone marrow suppression (due to the short range of alpha particles).
What is the route of excretion for radium-223?
Gastrointestinal
What precautions should be taken for a pt taking radium-223?
- Soiled clothing and boldly fluids should be handled with gloves
- Clothes should be laundered seperately
Note: The general population is safe due to the low gamma radiation (Radium-223 is mostly an alpha emitter).
How long after taking radium-223 should a pt use contraception?
For at least 6 months
Does radiopharmaceutical therapy for bone mets improve survival?
Generally no
Note: The exception is using Radium-223 to treat prostate cancer bone mets, which does seem to improve survival.
How does Yttrium-90 work?
It is a beta emitter, destroying tissue near where it is injected
What is the maximum tissue penetration of Y-90?
10 mm
Note: This is why Y-90 treatment spares most of the surrounding healthy liver tissue.
Why is it important to do a Tc-99m MAA hepatic arterial injection prior to treatment with Y-90?
To identify a lung shunt fraction (should be less than 10% ideally, not more than 20%)
Note: If the lung shunt fraction is > 20%, the risk of radiation pneumonitis is too high.
What does the lung shunt fraction need to be in order to do Y-90?
Less than 20% (less than 10% is ideal, but 10-20% is ok you just have to reduce the Y-90 dose)
Note: If > 20%, the risk of radiation pneumonitis is too high.
What is the optimal particle size for Y-90 embolization?
20-40 micrometers
Note: This size allows particles to get stuck in tumor nodules without fully obstructing blood flow (some blood flow is needed to help generate free radicals).
What is the typical dose used for Y-90 embolization?
100-1000 Gy
What are the Y-90 photopeaks that can be used for imaging?
- 175 keV
- 185 keV
What is the half life of Y-90?
2.67 days
What is radioimmune therapy?
The use of Y-90 labeled monoclonal antibodies to treat cancer
Note: This is mostly used for refractory non-Hodgkin lymphoma.
How do you perform radioimmune therapy?
First, In-111 labeled monoclonal antibodies are given for imaging (to ensure the biodistribution is good, that the antibodies only go where you want them to go)
Then, you give Y-90 labeled monoclonal antibodies to treat that distribution
Which monoclonal antibody is often used for radioimmune therapy of refractory non-Hodgkins lymphoma?
Ibritumomab tiuxetan (Zevalin)
Note: This antibody binds to the CD-20 receptors on B-cells.
What does platelet level need to be to receive radioimmune therapy for non-Hodgkins lymphoma?
Greater than 100,000
What is the most common side effect of radioimmune therapy for non-Hodgkins lymphoma?
Thrombocytopenia and neutropenia (90% of cases)
What is considered altered distribution of In-111 Zevalin (meaning that you should not treat with Y-90 Zevalin)?
- Bone marrow uptake > 25%
- Fixed uptake in the bowel (or bowel uptake greater than liver)
- Uptake in the kidneys greater than the liver on day 3
- Uptake in the lungs greater than the heart on day 1
- Uptake in the lungs greater than the liver on days 2 or 3
Does radioimune therapy for non-Hodgkin lymphoma need to occur as an inpatient? Or can the pt be released home?
They can be released home (dose to the general population is low enough)
Note: They should sleep alone and take other precautions for the first week or so.
Protocol for radioimmune therapy for non-Hodgkins lymphoma
- Give rituximab (to block the CD20 receptors on circulating B cells and in the spleen)
- Give In-111 Zevalin to see if there is altered biodistribution (get delayed images at 90-120 hours if you think it might be altered)
- If normal biodistribution, give Y-90 Zevalin
