Usefulness of Quantitative Bone Single-Photon Emission Computed Tomography/Computed Tomography for Evaluating the Treatment Response of Bone Metastasis in a Lung Cancer Patient

We report a case of bone metastasis arising from lung cancer, including quantitative values obtained with bone single-photon emission computed tomography/computed tomography (SPECT/CT), which were useful to evaluate the treatment response. The first bone SPECT/CT during pembrolizumab therapy for lung cancer recurrence showed intense ^99mTc-HMDP uptake of the right femur head and mild uptake of the left ribs. After the palliative radiotherapy for the right femur head metastasis and chemotherapy, the second bone SPECT/CT showed a decrease in focal uptake of the right femur hip and increasing uptake of the left ribs. There was also new uptake appearance in the sternum, right rib, spine (Th2, Th9, Th12, L4, S1), and bilateral pelvic bone (left ilium, acetabular cartridge, femur, right ilium and ischium). The change of maximum standardized uptake values (SUVmax) for the right femur head and left third and eighth rib bony metastases were −72.6% (from 22.96 to 6.28), +407.7% (from 2.97 to 15.08), and +229.2% (from 2.60 to 8.56), respectively. The change of whole-lesion metabolic bone volume and total bone uptake was +235.4% (from 22.75 to 76.3 cm³) and +219.1% (from 205.0 to 654.09), respectively. Two quantitative bone SPECT/CT images clearly showed the good response of femur head metastasis due to radiotherapy, and progression of other bone metastases regardless of chemotherapy.