Radioactive Strontium is Being Used to Treat Cancer

Isotus

What is Radiation? What Type of Radiation Does Strontium 89 Emmit?

When an atom is unstable, it will try to stabilize itself by emitting waves or subatomic particles. The energy includes things like light and heat, as well  as radio waves, microwaves, infrared, ultraviolet, and gamma rays. 

Strontium emits Beta negative type radiation, which are negatively charged electrons.

How Radioactive Isotopes Decay

Radioactive isotopes decay by releasing energy in the form of waves or particles. 

In the case of α type radiation, a nucleus is unbalanced because the ratio of protons to neutrons is uneven. The protons, which are positively charged, will push each other away without enough neutrons to stabilize it. 

The unstable nucleus will emit an alpha particle which is a atom that consists of two protons and two neutrons. By losing this alpha particle, the original atom loses four atomic weight and two atomic numbers, meaning the element type moves back the periodic table by two. This is shown in the diagram below.

Alpha Decay - Alpha Radioactivity

Alpha Radiation n.d., Image, Radiation Dosimetry, viewed 19 September 2020, <https://www.radiation-dosimetry.org/what-is-alpha-decay-alpha-radioactivity-definition/>.  

In the case of β radiation, a neutron changes to a proton by releasing a negative charge, or an electron. The original nucleus therefore gains one proton, but loses an neutron, which means the mass stays the same, but the element number increases by one, moving the element up one space of the periodic table.

beta decay

Beta Radiation n.d., Image, Radiation Dosimetry, viewed 19 September 2020, <https://www.radiation-dosimetry.org/what-is-beta-particle-definition/>.  

About Strontium 89

Strontium 89 has a half life of 50.6 days, after which it decays to Yttrium 89. It has an average β radiation  of 1.46 MeV.When used medically, Strontium 89 takes the form of Metastron, which is a “sterile, non-pyrogenic, aqueous solution of Strontium-89 Chloride for intravenous administration. The solution contains no preservative.” (Metastron, 2013). Strontium 89 is produced by nuclear fission. It can also be formed from the beta decay of Germanium 89, Arsenic 89, Arsenic 90, and Arsenic 91, which is shown in the diagram to the right.

Isotope Sr-89 Chloride for Injection

Strontium 89 n.d., Image, ISMI, viewed 19 September 2020, <https://www.ismi.ie/medical-solutions/isotopes/sr-89.html>.  

Decay Chain Image

Decay path of Strontium 89 n.d., Image, Wolfram Research, Inc., viewed 19 September 2020, <https://periodictable.com/Isotopes/038.89/index2.html>.  

How Strontium 89 is Used in Medicine

Strontium 89 is used for the treatment of bone metastases. A metastasis is a cancer that has originated in a part of the body and has spread to somewhere else. In the case of a bone metastasis, the original site of the cancer is usually the prostate, as prostate cancer has an affinity to travel to the bone. With bone metastases, there are usually multiple sites of the cancer. Because of this, it is not viable to use radiotherapy as there is too much risk to irradiate other parts of the body. This is why Strontium 89 is very useful. The radioactive Strontium is administered intravenously. As it is chemically similar to calcium, which is an important element for bone growth, it is absorbed by the bone in and around the metastatic region. The β radiation then kills off the cancerous cells before being eliminated through the kidneys.

Possible Side Effects

As the Strontium is administered intravenously, most patients will experience a 20-50% drop in platelet count. About 10% of patients may experience a short increase in bone pain about 1-2 weeks after the administration of the Strontium. Bone marrow toxicity is also prominent in patients, especially with platelets and white blood cells. Other common side effects include facial flushing and diarrhea

Necessary Precautions

As it is eliminated through the kidneys, it is important to carefully dispose of the patient’s urine for 7-10 days after the administration of Strontium 89. The maximum range of the radiation in tissue is 8mm, and the average range is 2.4mm, this means that there is minimal risk to tissues distant from the cancerous area. There is also no risk to family members or staff as Strontium 89 primarily emits β radiation which can be stopped by a thin sheet of aluminum or other similar materials. 

It is also not advised to use Metastron in patients with badly damaged bone marrow. Because bone marrow toxicity is a prominent side effect, it is advised to monitor the patient’s blood cell counts every second week.

How Strontium 89 Compares to Other Treatment Methods

Strontium 89 was approved as a treatment for metastatic prostate cancer in 1993. At the time, it was very useful as it provided a safer alternative to traditional methods. Strontium 89 provided an alternative to using radiotherapy to treat multiple areas of the body, which poses a significant risk to other organs, especially when multiple areas have to be treated. This method allowed for multiple areas to be targeted with minimal risk of radiation exposure to vital organs, staff, and family members.

However, this method is now outdated, as newer treatments such as hormone therapy have proved to be more effective. Hormone therapy doesn’t use radiation, so there is no risk of radiation damage to vital organs, staff, or family members. However the hormone used does block testosterone, which results in many undesirable side effects such as hot flushes, mood swings, irritability, and impotency in men. However, when the cancer is hormone resistant, radioactive Strontium is an available alternative.

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