Refining Treatment for Patients with Spinal Metastases

Chapter 1: Introduction
The increasing number of patients with spinal metastases requires more effective care. This thesis examines how emerging concepts in prognosis, radiotherapy, and image-guided spine surgery can help refine treatment strategies for these patients.

Chapter 2: Prognostic Models for Survival
This retrospective study evaluated twelve models predicting three, six, and twelve month survival in 953 patients with spinal metastases referred to the UMC Utrecht. Four models performed reasonably well, while most underestimated survival, especially in patients with poor predicted outcomes. Frequent recalibration using recent data is necessary to ensure that these models remain accurate and clinically useful.

Chapter 3: Stereotactic Radiotherapy for Painful Bone Metastases
A systematic review and meta-analysis of eighteen studies, including eight randomized trials, showed no difference in overall pain response between conventional and stereotactic radiotherapy at one, three, or six months. However, complete pain relief was more frequent after stereotactic treatment. Further analysis of individual patient data is needed to identify subgroups that benefit most.

Chapter 4: Intraoperative Three-Dimensional Imaging in Spine Surgery
In this survey, twenty-one spine surgeons evaluated pedicle screw positions in a simulated setting using both two-dimensional and three-dimensional imaging. Surgeons were more likely to decide to reposition screws after viewing three-dimensional images, even if the screws were already acceptably placed. These findings highlight both the potential of advanced imaging and the need for clear guidelines to avoid unnecessary interventions.

Chapter 5: Cervical Pedicle Screw Placement
A systematic review and meta-analysis of eighteen observational studies found no significant difference in accuracy between screw placement with or without intraoperative navigation. Still, navigation may support new possibilities, such as minimally invasive techniques, particularly in anatomically complex regions.

Chapter 6: Navigated Percutaneous Spine Surgery
This phantom study tested a new navigation system for percutaneous screw placement. A surgeon inserted screws in lumbar vertebrae using only the navigation interface. The system showed good usability, but improvements in accuracy and workflow are needed to ensure consistent performance in clinical settings.

Chapter 7: Three-Dimensional to Two-Dimensional Registration Using Skin Markers
This study assessed a new registration algorithm using non-invasive skin markers in three human cadavers. The algorithm achieved a median registration error of 0.51 millimeters and accurately registered up to five adjacent vertebrae. Integration into a full navigation system is the next step.

Chapter 8: General Discussion
Simple models such as the Bollen model can support shared decision-making but require regular updating. Stereotactic radiotherapy may provide more effective pain relief in selected patients, but broader use is limited by cost and complexity. Innovations including artificial intelligence based planning and synthetic imaging may improve feasibility. Navigation and advanced imaging technologies can expand surgical capacity and enable safer procedures, even for less experienced surgeons, provided they are applied with clear clinical justification.

Chapter 9: Conclusion
Inspired by Mondrian’s structured view of complexity, this thesis emphasizes that clinical innovation should simplify care rather than complicate it. Progress in treating spinal metastases depends on aligning advanced technology with clear purpose, practical workflows, and a strong focus on patient needs.