| We are seeing a lot more metastatic bone disease today and dealing with the associated pain can be a major challenge in palliative care. Where does the use of Strontium 89 fit in to the therapeutic approach to bone pain? The following lecture notes will help us to understand the role of Strontium 89. ~ Dr Andrew Binns
Notes from the lecture delivered to the Fourth Annual Symposium of the Institute of Palliative Medicine in March 1995 by Dr Michael Boyer, staff specialist oncologist, RPAH. These notes have been reproduced from the society's October 1995 newsletter with permission from the management committee and the author.
Strontium 89 (Metastron) has been used around the world for some time, but it is only recently available in Australia. It is a pure beta emitter with a half life of 50 days. It is expensive, costing more than $2000 per dose. It is administered as an intravenous injection of an aqueous solution. Brays travel only to a depth of 1-2 mm in human tissue, can't be used for imaging and are little risk to others.
Strontium 'imitates' the behaviour of calcium: ie. is taken up and incorporated into bone. There is preferential retention in metastatic lesions compared to normal bone. It is not known why this occurs. The total body retention of strontium 89 therefore depends on the extent of the metastatic bone disease.
It has also been used in sclerotic metastases from other primaries including breast and unknown primary.
It is excreted in the urine (90%) and bile (10%). The majority of the dose is excreted in the first 48 hours after injection.
Results:
In single arm studies, improvement in pain from 'widespread' prostatic sclerotic bony metastases was demonstrated in 60-80% of treated patients.
Only one small (32 patients) double blind study comparing strontium 89 with placebo has been carried out. Complete relief of pain was achieved in 15% of treated patients vs 0% of the untreated group.
Randomised trials have shown results equal to the use of hemibody radiotherapy in terms of survival and pain relief, but better results with regard to the development of and number of new sites of pain (decreased by 20-30%).
Side effects:
There is less GIT toxicity than hemibody radiation and similar haematological toxicity.
The major toxicity is haematological, especially thrombocytopaenia. Typically there is a 20-40% fall in platelet count with the nadir at about six weeks after the injection.
There is occasionally a transient flare in pain.
Because of urinary excretion, low levels of radiation will be present in the urine for up to 10 days. Care must be taken in handling urine during this time. Patients need to take care with personal hygiene during this time and to double flush the toilet.
It is not considered to be 'environmentally damaging'.
In general it is suggested for patients with sclerotic metastases who cannot get relief any other way who have diffuse pain. It is not approved for use with lytic secondaries.
It is typically repeated once at three months.
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