Digital tomosynthesis for follow-up imaging of upper thoracic spine metastases: A novel case application

Abstract

We report a case demonstrating the utility of digital tomosynthesis (DTS) for follow-up imaging of a metastatic tumor in the upper thoracic spine. A 64-year-old woman presented with progressive lower extremity numbness and gait disturbance. Imaging revealed a pathologic fracture of the T3 vertebra secondary to metastatic lung cancer. The patient was treated with a cervicothoracic brace, radiation therapy, denosumab, and osimertinib. DTS performed 2 weeks after admission revealed a lytic lesion, and follow-up DTS at 16 weeks demonstrated bone sclerosis, indicating a positive treatment response. The patient remained neurologically intact and was able to discontinue brace use. Conventional radiography is limited in visualizing the upper thoracic spine due to shoulder overlap, while CT involves higher radiation exposure. DTS enabled early detection of lytic changes and subsequent sclerosis, demonstrating its value in visualizing treatment response during follow-up. This case highlights the potential of DTS as a practical follow-up imaging modality in oncologic spine care.

Introduction

Metastatic spinal tumors are a common and serious complication of advanced malignancies, often leading to pain, neurological deficits, and spinal instability. Early detection and continuous monitoring of vertebral metastases are essential to prevent deterioration and guide treatment decisions [1]. However, imaging of the upper thoracic spine remains technically challenging due to anatomical overlap from the shoulder girdle [2].

Computed tomography (CT) offers high-resolution bone detail but is associated with high radiation exposure, while magnetic resonance imaging (MRI) is limited in bone assessment and cost-effectiveness for serial use. Digital tomosynthesis (DTS) has recently emerged as a promising imaging modality that combines tomographic reconstruction with low radiation exposure [3].

In this report, we present a case of upper thoracic spinal metastasis from lung cancer in which DTS was used effectively to monitor treatment response. This case highlights the clinical applicability of DTS in oncologic spine care and discusses its technical advantages, limitations, and potential role in follow-up imaging algorithms.

Case presentation

A 64-year-old Japanese woman with no significant prior medical history presented with back pain. She was referred to our clinic due to progressive lower extremity numbness, weakness, and gait disturbance. Muscle strength was graded as 4/5 in the right and 5/5 in the left lower extremity. Sensory deficits in pain and touch were noted below the T5 level. Upon admission, the patient was afebrile with stable vital signs. Neurologically, she exhibited hypoesthesia below the T5 dermatome and mildly reduced strength in the right lower limb, without bowel or bladder dysfunction.

Thoracic spine X-ray imaging demonstrated an obscured pedicle sign and a compression fracture at the T3 vertebra (Fig. 1A and B). A chest radiograph obtained at admission (Fig. 1C) revealed an infiltrative shadow in the right lower lung field, suggestive of a primary pulmonary lesion. Computed tomography (CT) confirmed the compression fracture and revealed lytic changes in the T3 vertebra and spinous process (Fig. 1D). Magnetic resonance imaging (MRI) showed a pathologic fracture of the T3 vertebral body, spinal cord compression, and signal alterations in the adjacent posterior soft tissue (Fig. 1E). Enhanced CT further confirmed a metastatic thoracic tumor, originating from a primary lung cancer (Fig. 1F and G). A bronchoscopy biopsy of the right lower lobe lesion revealed squamous cell carcinoma of the lung, confirming the histological diagnosis.

Fig. 1.

Multimodality imaging at presentation. (A, B) Thoracic spine X-rays in anteroposterior and lateral views show partial obscuration of the T3 pedicle (arrowhead), suggesting structural compromise. (C) Chest X-ray (anteroposterior view) demonstrates an infiltrative opacity in the right lower lung field (arrow), corresponding to the primary lung tumor. (D) Sagittal CT image reveals a compression fracture and lytic destruction of the T3 vertebral body (arrowhead). (E) Sagittal T2-weighted MRI shows a low-signal T3 vertebral body with epidural compression and adjacent posterior soft tissue changes and (F, G) Enhanced CT in coronal and axial planes confirms a lytic lesion in T3 (arrowhead) and a solid mass in the right lower lobe of the lung (arrow). Findings are consistent with metastatic spinal involvement from primary lung cancer.

According to the new Katagiri prognostic scoring system for skeletal metastases [4], her score was 6, corresponding to a 68% 1-year survival rate and a 55% 2-year survival rate. The Spine Instability Neoplastic Score (SINS) was 11, indicating mild instability [5].

Management and outcome

The management plan is summarized in Fig. 2. She was fitted with a cervicothoracic orthosis (Aspen CTO®) and underwent radiation therapy to the T3 vertebra (total 50 Gy over 5 sessions), along with monthly denosumab (Ranmark®) administration for 5 months. Six weeks later, chemotherapy with osimertinib (Tagrisso®) was initiated.

Fig. 2.

Timeline of the patient’s treatment plan for metastatic spinal tumor and primary lung cancer. The patient received initial spinal stabilization with a cervicothoracic orthosis (CTO), followed by radiotherapy (RT), monthly denosumab, and later osimertinib therapy. Neurological status and bone remodeling were monitored throughout.

DTS imaging performed 2 weeks postadmission clearly visualized the lytic lesion at T3 (Fig. 3). Throughout the 4-month treatment course, serial DTS scans were performed at weeks 2 and 16. Progressive bone sclerosis in the T3 vertebra was clearly observed, corresponding with symptomatic improvement and brace discontinuation at week 20. Throughout treatment, the patient remained neurologically intact and was eventually able to discontinue use of the cervicothoracic brace.

Fig. 3.

Digital tomosynthesis (DTS) follow-up of the T3 vertebral lesion. DTS obtained at 2 weeks postadmission shows a sharply marginated lytic lesion in the T3 vertebral body (arrowhead), consistent with osseous metastasis. At 16 weeks, DTS reveals progressive bone sclerosis at T3 (arrowhead), indicating a favorable response to multimodal therapy. DTS provided clear visualization of cortical remodeling with lower radiation dose compared to conventional CT, allowing effective longitudinal monitoring.

Discussion

In this case, DTS was selected over CT for interim follow-up due to the patient’s need for frequent imaging and the anatomical challenge of upper thoracic visualization on plain radiographs. The clear demonstration of bone sclerosis on DTS directly supported clinical decisions, including the discontinuation of the brace.

Early detection and continuous monitoring are critical for optimizing the management of metastatic spinal tumors, aiming to achieve pain control, preserve or restore neurologic function, maintain spinal stability, and enhance health-related quality of life [1]. However, conventional radiography often provides limited visualization of the upper thoracic spine due to shoulder girdle overlap [2]. Although CT offers superior imaging detail, its use is constrained by concerns regarding radiation exposure and cost [6].

DTS addresses several limitations of conventional imaging modalities in the thoracic spine. It generates tomographic images with reduced anatomical overlap compared to standard radiography and entails substantially lower radiation exposure than CT, making it suitable for serial imaging. Previous studies have shown its utility in evaluating thoracic spine pathology, particularly in the elderly and in trauma settings[7]. In this case, DTS was performed using the Sonialvision Safire 17 system (Shimadzu, Kyoto, Japan). The scan was acquired in the supine lateral projection, with a slice thickness of 2 mm and an acquisition time of approximately 10 seconds. This setup provided sufficient spatial resolution to monitor osseous changes while minimizing motion artifacts. Compared to CT, DTS offers a favorable balance of image quality, radiation dose, and cost, supporting its use in serial oncologic surveillance.

In patients with lung cancer and spinal metastases, multidisciplinary therapy—including radiotherapy, chemotherapy, and bone-modifying agents—is essential to improve prognosis [8]. In this context, DTS offers a practical and low-dose imaging option for longitudinal monitoring of osseous metastases, aligning with the ALARA principle and potentially improving patient safety during follow-up.

While DTS may not replace CT or MRI in cases requiring detailed soft tissue assessment or evaluation of spinal canal compromise, it can be particularly valuable for follow-up of stable osseous lesions, patients with low-to-moderate instability, or those requiring frequent imaging with minimized radiation exposure. In contrast, high-risk cases with neurological involvement or dominant soft tissue pathology remain best evaluated by MRI or contrast-enhanced CT. These considerations may help guide the appropriate integration of DTS into clinical follow-up strategies.

While MRI remains indispensable for neural element assessment, DTS may offer a low-cost adjunct in the follow-up of stable spinal metastases, osteoblastic response monitoring, or sclerotic bone tumors such as prostate or breast cancer metastases. Future studies should aim to define precise clinical guidelines for DTS use across tumor types and spine regions.

Conclusion

This clinical report underscores the potential utility of digital tomosynthesis (DTS) as a low-radiation, cost-effective modality for longitudinal follow-up of metastatic spinal tumors. In particular, DTS may be beneficial in stable osseous lesions or in patients requiring frequent monitoring where minimizing radiation is critical. Its ability to visualize subtle changes in bone architecture enables early assessment of treatment response.

As imaging strategies evolve, DTS could play a valuable role within clinical algorithms for oncologic spine surveillance, especially when used in conjunction with CT and MRI. Further prospective studies are needed to define standardized indications, diagnostic performance, and integration with multidisciplinary care protocols.

Patient consent

Informed consent for publication of this case was obtained from the patient. All procedures were conducted in accordance with institutional guidelines and ethical standards.