Decoding Radium 223 for Prostate Cancer

Radium 223 (also known as radium 223 dichloride or Xofigo) is a radioactive isotope, an unstable version of a chemical element which decays over time, emitting radiation. The alpha particle radiation it releases is used as radiation therapy to target and eliminate bone metastases. It is approved by the FDA for treatment in metastatic castration resistant prostate cancer which has noticeably spread to the bones, but has not yet shown visceral metastasis.

With features that mimic natural calcium, radium 223 then replaces calcium as it is preferentially picked up by hydroxyapatite, a mineral in the bones critical for bone regeneration. This binding process releases a high amount of energy, which then damages cancer cells by introducing double-stranded DNA breaks. This disables their ability to self-repair, thus hindering their ability to spread further.

Furthermore, alpha particle radiation can only travel up to about six cell diameters wide, limiting its reach to other healthy tissues, and reducing the potential damage it could cause.

As a radioactive material, radium 223 may pose risks to your caregivers, family and medical staff. During the treatment course and for a short time after completing it, radiation exposure is possible through bodily fluids (e.g. urine, feces or vomit).

While there is no need to restrict personal contact, some good guidelines to follow post-treatment (for at least a week after treatment completion) include:

• Flushing the toilet several times after each use
• Protective glove use and regular hand washing by your caregivers
• Washing clothes soiled with your fecal matter or urine quickly and separately from other clothes
• Contraceptive use for male patients, as well as partners of reproductive potential, due to the risk of fetal harm (this should be done until six months after treatment completion)

Other key features you should know about your radium 223 treatment:

• The recommended dose schedule is currently a total of six intravenous injections, with intervals of four weeks in between
• A recurring check of your blood count will likely be recommended to ensure that your blood cell production recovers to acceptable levels after treatment
• Signs of bleeding, infections, dehydration or issues with fully emptying your bladder should be reported to your healthcare provider
• If you intend to conceive after, you should note that there is a risk of infertility for you. Unfortunately, this risk is generally commonly associated with prostate cancer treatments, as most target the reduction of the sex hormones, or the removal of the prostate in order to limit cancer spread

Some commonly reported side effects affecting more than one in ten people include:

• Nausea, diarrhea, vomiting
• Swelling in the extremities of the body (e.g. arms, legs, hands, feet)
• Low blood cell counts (e.g. red blood cells, white blood cells, and platelets)

Other side effects may include dehydration, redness, pain or swelling at the injection site, and reduced fertility. As a radiotherapy-based treatment, radium 223 may also increase your long-term cumulative radiation exposure, which is associated with an increased risk of secondary cancers. Unfortunately, there is limited data on this, as these cancers are expected to take a longer time to develop than the length of most clinical trials.

Radium 223 is now known as a well-established life-prolonging option for one subset of castration-resistant metastatic prostate cancer patients, those with metastasis mainly limited to the bones. However, our next challenge would then be to ensure the most optimal patient selection for this treatment. The answer to this may lie in new research on biomarkers, which may allow clinicians to predict patient responses to radium 223 more effectively and accurately in the future.