Does a DEXA scan show cancer?
No, DEXA scans cannot detect cancer. However, DEXA scans may be important for cancer patients to monitor losses in bone density due to treatment. Keep reading to learn more about how DEXA scans work and what conditions they can effectively detect.
What is a DEXA scan?
A DEXA scan, also called a bone densitometry scan, is a radiological exam used to determine bone mineral density (BMD) [1]. DEXA scans are non-invasive and can be performed quickly (approximately 10-20 minutes) in an outpatient radiology clinic [1]. During the scan, individuals lie on a padded table with a maneuverable x-ray detector arm positioned above them. The technician moves the detector over various areas of the body—typically the lower (lumbar) spine, pelvis, and hip—to capture densitometry readings [2].
How does a DEXA scan work?
During the procedure, the DEXA machine emits low levels of x-ray radiation of two distinct energy levels, one of which is absorbed by soft tissue and the other by bone. The amount of x-ray energy absorbed by soft tissue is subtracted from the total amount of energy absorbed by the body to calculate the approximate amount of energy absorbed by bone. This number is then processed by specialized computer software to calculate the bone density of the region [2].
The results of a DEXA scan are reported in the form of T scores and Z scores. The T score compares an individual’s bone density to that of a young adult of the same gender with peak bone mass [2]. The Z score compares an individual’s bone density to other individuals of approximately the same size, gender, and age group as the patient [2]. Thus, T scores and Z scores are relative (i.e., based on comparison to an average) rather than absolute measures of bone density.
What conditions can a DEXA scan detect?
DEXA scans can detect the following conditions [2]:
- Osteopenia: osteopenia is a condition of moderately low bone mass and is defined by a T score between –1.1 and –2.4.
- Osteoporosis: osteoporosis is a more severe form of low bone mass and is defined by a T score of –2.5 or greater.
The results of a DEXA scan may be used to predict an individual’s risk of future bone fracture and guide appropriate treatment aimed at increasing bone density [3].
Will a bone density scan show cancer?
No, a DEXA scan cannot indicate cancer. A different type of bone scan called bone scintigraphy may be used to detect bone cancers and metastases [4]. In bone scintigraphy, patients are injected with a small amount of a radioactive substance that accumulates within areas of the bone that have undergone abnormal physical or chemical changes [4]. These areas are termed “hot spots.” As the radioactive substance decays, it emits gamma rays from the hot spots. These gamma rays can be detected by a scanner and used to locate areas of concern [4].
Bone scintigraphy is distinct from DEXA scanning and is used to identify different conditions. Notably, bone scintigraphy is considered invasive because it involves the injection of a radioactive substance rather than external x-ray radiation. In contrast to DEXA scans, bone scintigraphy can detect malignant bone cancers or metastatic bone cancer [4]. Bone scintigraphy can also detect other bone disorders such as arthritis, bone infection, avascular necrosis (death of bone tissue due to loss of circulation), and Paget’s disease [4].
Nevertheless, patients receiving cancer treatment may undergo DEXA scanning to assess their bone density. This is because certain cancer treatments such as chemotherapy, radiation, and hormonal drugs can lead to decreased bone mass [1]. For example, aromatase inhibitors have been associated with bone loss and therefore DEXA scans are often recommended for women with breast cancer [1]. Thus, DEXA scans may be used to monitor patients’ bone mass during and following treatment, but are not used to detect cancer or assess cancer progression.
DEXA scans and cancer risk
Because DEXA scans involve exposing the body to x-ray radiation, there is a small risk of inducing potentially oncogenic mutations. This risk exists for any procedure that involves exposure to radiation or radioactive substances. However, because the level of radiation used in DEXA scanning is low and the procedure is performed infrequently, the risk of cancer development associated with DEXA scans is considered minimal [2].
Conclusion
DEXA scans are a type of radiologic exam used to assess bone mineral density. It is most frequently prescribed to individuals at risk of bone loss or who have experienced unexplained fractures. The procedure uses low levels of x-ray radiation to determine an individual’s bone density and compares the results against a reference population, which generates two outputs: T scores and Z scores. These quantities can reveal conditions such as osteopenia and osteoporosis. DEXA scans cannot detect cancer, but may be recommended to cancer patients who are at risk of bone loss due to treatment.