Characterization of radiation-induced photopenic abnormalities on bone scans.

Photopenic abnormalities induced by radiation therapy are important to recognize on bone scans, since they often affect longitudinal or lateral symmetry. This phenomenon was studied in 43 patients treated through 67 ports (including the axial skeleton). Bone doses spanned 450-6,700 R (mean +/- S.D. = 3,600 +/- 1,700 R), and the interval from the midpoint of therapy to the time of the scan was 1-19 months. Photopenic defects appeared between 4 and 6 months after therapy. Of 20 patients (31 ports) studied more than 4 months after therapy, 14 (45%) had such defects. None was detected in regions receiving less than 2,000 R. The authors conclude that knowledge of a patient's radiotherapy history is an important prerequisite to interpretation of subsequent bone scans.