[The early changes in bone mineral metabolism due to radiation--measurement of bone mineral density in lumbar vertebra by quantitative computed tomography].

Osteosclerosis, osteonecrosis and compression fracture are commonly observed several years after radiation. Since lumbago usually occurs several months after radiation, the possibility that bone mineral metabolism is disturbed during and immediately after radiation cannot be ruled out. However, there have been no reports concerning early changes in bone mineral metabolism due to radiation. The bone mineral density was measured by QCT (Quantitative Computed Tomography) in 30 normal non-radiated cases and 14 radiated cases to investigate the changes in bone mineral metabolism due to radiation. The bone mineral density (QCT-Value: QCT-V) in the 3rd lumbar vertebra (L3) of normal non-radiated subjects decreased linearly with age (Y = 291.114447-3.01473X). The QCT-V of the 5th lumbar vertebra (L5) of normal cases also decreased linearly with age (Y = 309.641397-3.03986X), resembling that of L3. The ratio of the QCT-V of L5 to L3 (L5/L3, expressed as a percentage) definitely increased with age (Y = 86.5657441 + 0.58885064X). In radiated cases, the QCT-V of L3 in the non-radiated field did not change appreciably. The QCT-V of L5 in the radiated field was decreased from 20GY and reached 53.08 +/- 17.37% of the pre-radiation value after 50GY. The L5/L3 ratio was also decreased from 20GY and reached 55.47 +/- 15.32% of the pre-radiation value after 50GY. It becomes apparent that the QCT-V of the radiated lumbar vertebra is decreased during radiation. It is suggested that bone mineral metabolism may be disturbed in the early phase of radiation.