Performance and analysis of vertebral ⁹⁹Tc^m-MDP uptake after chest tumor radiotherapy

Objective To analyze the changes in vertebral ⁹⁹Tc^m-medronate (MDP) uptake and the correlation with clinical radiotherapy parameters in chest tumor patients.

Methods A retrospective study was conducted in 110 patients (including 62 males and 48 females aged 58.2 ± 11.9 years) who underwent chest tumor radiotherapy in Shandong Cancer Hospital from April 20, 2014 to October 31, 2018, and whole-body bone scan was performed before and after radiotherapy. The clinical information, tumor factors, and radiotherapy plan were analyzed using semiquantitative analysis. The results of the bone scan were divided into normal and abnormal vertebral uptake groups. In accordance with the time interval of bone imaging before and after radiotherapy, the patients were further classified into groups, namely, 60–120 (23 cases), 121–180 (30 cases), 181–240 (27 cases), and 241–365 (30 cases) days. The comparison among groups were analyzed using the χ² test, and the statistical results were analyzed using the binary classification logistic regression. The change in the vertebral body ⁹⁹Tc^m-MDP uptake and the correlation with clinical radiotherapy parameters in chest tumor patients were discussed. The (T/N_before) − (T/N_after)/(T/N_before) was calculated, and the receiver operating characteristic curve was drawn. The best diagnosis threshold of vertebral ⁹⁹Tc^m-MDP uptake abnormality was found.

Results In 110 patients, 48 (43.6%) had local poor vertebral radioactivity uptake with minimum, maximum, and average vertebral exposure doses of 1039.5, 4488.7, and (2139.5±839.8) cGy, respectively. The shortest, longest, and median imaging interval was 61, 326, and 160 days, respectively. The remaining 62 patients (56.4%) had no obvious abnormal radioactive uptake. The degree of vertebral body uptake was correlated with the radiotherapy dose (χ²=4.401, P=0.036), radiotherapy frequency (χ²=2.241, P=0.027), vertebral body irradiation dose (χ²=5.913, P=0.015), and imaging interval before and after radiotherapy (χ²=12.542, P=0.013). No statistical correlation with age, gender, body mass index, single radiotherapy dose, planning target volume, planning target volume dose, vertebral irradiation volume, and distance from the radiotherapy center to the vertebral center was observed. In the grouped imaging intervals and compared groups, a difference was observed among 60–120, 121–180 days and 181–240, 241–365 days in vertebral body uptake (χ²=3.850–15.492, all P>0.05), and the abnormal vertebral ⁹⁹Tc^m-MDP uptake at intervals less than 180 days accounted for 66.7% (32/48). The sensitivity and specificity of evaluating the ⁹⁹Tc^m-MDP uptake abnormality were 74.6% and 82.9%, respectively. The area under the curve was 0.934 by the the receiver operating characteristic curve, indicating that (T/N_before)−(T/N_after)/(T/N_before) was good at evaluating the change rate of vertebral ⁹⁹Tc^m-MDP uptake, and the optimal diagnostic threshold for vertebral ⁹⁹Tc^m-MDP uptake abnormality was 0.161.

Conclusions Early imaging time after radiotherapy results in high detection rate of vertebral injury. The change in vertebral body ⁹⁹Tc^m-MDP uptake can reflect the degree of radioactive vertebral damage to some extent.