Effective Dose and Effective Risk from Post–Single Photon Emission Computed Tomography Imaging of the Lumbar Spine

Purpose: Planar bone scans play an important role in the staging and monitoring of malignancy and metastases. Metastases in the lumbar spine are associated with significant morbidity; therefore, accurate diagnosis is essential. Supplementary imaging after planar bone scans is often required to characterize lesions; however, this is associated with additional radiation dose. This article provides information on the comparative effective dose and effective risk from supplementary lumbar spine radiographs, low-dose computed tomography (LDCT), and diagnostic CT (DCT). Method: Organ dose was measured in a phantom using thermoluminescent dosimeters. Effective dose and effective risk were calculated for radiographs, LDCT, and DCT imaging of the lumbar spine. Results: Radiation dose was 0.56 mSv for the anteroposterior and lateral lumbar spine radiographs, 0.80 mSv for LDCT, and 3.78 mSv for DCT. Additional imaging resulted in an increase in effective dose of 12.28%, 17.54%, and 82.89% for radiographs, LDCT, and DCT, respectively. Risk of cancer induction decreased as age increased. The difference in risk between the modalities also decreased. Males had a statistically significant higher risk than female patients (P =.023), attributed to the sensitive organs being closer to the exposed area. Conclusions: Effective dose for LDCT is comparable with radiographs of the lumbar spine. With the known benefits of image fusion, it is recommended that LDCT replace radiograph imaging for characterization of lumbar spine lesions identified on planar bone scans. DCT is associated with significantly higher effective dose than LDCT. Effective risk is also higher, and the difference is more marked in younger female patients.