Bone density scans (Dexa)

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Many treatments for cancer can effect the amount of protein and calcium in the bone (the bone density). This may range from a mild reduction in the calcium density, measured on a bone density scan, to a moderate reduction called osteopenia through to a significant bone mineralisation loss with its associated risks of collapsed vertebrae and fractures. The amount of mineralisation of the bones can be measured with a dexa scanner.

Having a dexa scan

A DEXA scan is a painless test that measures the density of bones. DEXA stands for dual energy x-rays absorptiometry. There are two different types of DEXA scanning devices, central and peripheral. Central DEXA devices are large machines that can measure bone density in the centre of your skeleton, such as your hip and spine. Peripheral DEXA devices are smaller, portable machines that are used to measure bone density on the periphery of your skeleton, such as your wrist, heel or finger.

During a DEXA scan, you will be asked to lie on your back on a couch and to keep still while the scan is being taken. The scan usually takes between 10 and 20 minutes, depending on which part of your body is being examined, and whether a central or peripheral scanner is being used.

In order to check for osteoporosis, the doctor commonly scans the lower back bones (vertebrae) and hips. The forearm may also be scanned, because it has a different level of calcium content from other body parts.

No preparation for the test is required and, depending on which part of your body is being scanned, you may be able to remain fully dressed, in clothes without metal fastenings. It is a painless procedure and you can go straight home afterwards.

The information from the scanner is sent to a computer which calculates a score for the density of your bone. A low score indicates that the bone is less dense than it should be, and is more likely to break. If a DEXA scan shows that you have osteoporosis, you may be given advice and treatment to help strengthen your bones.

Who is eligible for a baseline DEXA scan

·       All post menopausal who are taking an Aromatase Inhibitor  (anastrazole, letrozole, exemestane) and the proposed treatment length is two years or more (first scan at the onset of treatment)

·       Postmenopausal women who have received chemotherapy not on tamoxifen

·       Pre-menopausal women who are taking tamoxifen.

·       Premature menopause (<45 years particularly induced by Zoladex, chemotherapy or oophorectomy)

·    Co-morbidities long term steroids, hypothyroidism, chronic renal failure

The management and rescanning interval is determined by the T-score:  

  * Z score (age adjusted) if < -2 refer patient to endocrine physician to investigate for endocrine abnormalities.

Other comments:

·       Oral Bisphosphonate prescribing; eg Risedronate 35mg or Aledronate 70mg PO once weekly. Always co-prescribe a calcium/vitamin D supplement such as Adacal-D₃ one per day.

·       Weekly bisphosphonate dosing is effective, better tolerated than daily (avoids daily insult to oesophagus) with better compliance. 

·       Dosing instructions are critical and should be reinforced at follow-up visit: take first thing in the morning, follow by drink of water, sit upright for 30 minutes, do not take lying down and do not eat or drink for 30 minutes after taking the tablet.. 

·       DEXA response to bisphosphonates is virtually universal (failure of response is a sign of non-compliance), so no need to rescan until end of five year course (more valuable to spend time ensuring compliance at each follow up visit).

·       Bisphosphonates are absolutely contraindicated in pregnancy so make sure younger patients are aware of this and taking appropriate precautions, even if apparently menopausal. A 6 month washout period is needed after risedronate if attempting to conceive (which is the same as the recommended tamoxifen washout period).

·       Patients who cannot tolerate oral bisphosphonates and have T scores less than -2.5 should be given monthly pamidronate infusions for five years.  Other intravenous preparations as they become licensed may become preferable.