The advantage of 3D conformal treatment of lumbar spine metastases in comparison to traditional PA or AP-PA techniques: restoring an intermediate niche of therapeutic sophistication

BACKGROUND: To evaluate the effect of the 3D radiation field design on normal tissues compared with commonly used appositional fields in patients with lumbar spine metastases. METHODS AND MATERIALS: Ten comparative treatment plans for radiation of lumbar spine metastases were compared for posterior and anterior- posterior fields with 3D plans. RESULTS: The PTV coverage in all comparative plans was similar. V 15 of the bowel in 3D, AP-PA and PA plans was 6.7 Gy (SD 6.47), 39.8 Gy (SD 11.4) and 37.3 Gy (SD15.7), respectively (p < 0.0001). The mean dose to both kidneys was 9.6 Gy (SD 4.8), 4.1 Gy (SD 3.9) and 4.6 Gy (SD 4.4) for appropriate plans (p = 0.002). Maximal dose to the spinal cord was 30.6 Gy (SD 2.1), 33.1 Gy (SD 9.8) and 37.7 Gy (SD 2) for 3D, AP-PA and PA plans. CONCLUSION: 3D conformal treatment planning of lumbar vertebral metastases was significantly better in term of bowel and spinal cord exposure compared to AP-PA and PA techniques. The exposure of the kidneys in 3D plans, while greater than in the comparative plans, did not violate accepted dose-volume thresholds.