Abstract
BackgroundThe aim of this study was to quantify the variability in spinal radiosurgery (SRS) planning practices between five international institutions, all member of the Elekta Spine Radiosurgery Research Consortium.MethodsFour institutions provided one representative patient case each consisting of the medical history, CT and MR imaging. A step-wise planning approach was used where, after each planning step a consensus was generated that formed the basis for the next planning step. This allowed independent analysis of all planning steps of CT-MR image registration, GTV definition, CTV definition, PTV definition and SRS treatment planning. In addition, each institution generated one additional SRS plan for each case based on intra-institutional image registration and contouring, independent of consensus results.ResultsAveraged over the four cases, image registration variability ranged between translational 1.1 mm and 2.4 mm and rotational 1.1° and 2.0° in all three directions. GTV delineation variability was 1.5 mm in axial and 1.6 mm in longitudinal direction averaged for the four cases. CTV delineation variability was 0.8 mm in axial and 1.2 mm in longitudinal direction. CTV-to-PTV margins ranged between 0 mm and 2 mm according to institutional protocol. Delineation variability was 1 mm in axial directions for the spinal cord. Average PTV coverage for a single fraction18 Gy prescription was 87 ± 5 %; Dmin to the PTV was 7.5 ± 1.8 Gy averaged over all cases and institutions. Average Dmax to the PRV_SC (spinal cord + 1 mm) was 10.5 ± 1.6 Gy and the average Paddick conformity index was 0.69 ± 0.06.ConclusionsResults of this study reflect the variability in current practice of spine radiosurgery in large and highly experienced academic centers. Despite close methodical agreement in the daily workflow, clinically significant variability in all steps of the treatment planning process was demonstrated. This may translate into differences in patient clinical outcome and highlights the need for consensus and established delineation and planning criteria.
Highlights
Cancer patients with systemic tumor spread frequently develop skeletal metastases
Patient cases All centers were experienced in spine RS planning and delivery and were members of the Elekta Spine Radiosurgery Research Consortium which included University Hospital Wuerzburg, University of Pittsburgh School of Medicine, William Beaumont Hospital, Princess Margaret Hospital, University of Virginia School of Medicine
Step 4 delineation of PTV CTV-to-PTV margins ranged between 0 mm and 2 mm according to institutional protocol [17, 25]
Summary
Cancer patients with systemic tumor spread frequently develop skeletal metastases. Many of these occur within the spine [1,2,3]. Radiotherapy (RT) is an established and recommended component of the multidisciplinary treatment of spine metastases with regard to prevention of pathologic fractures or neurological deficits and pain palliation [4,5,6]. The use of SRS as an alternative treatment to conventional RT has been increasing rapidly. The aim of this study was to quantify the variability in spinal radiosurgery (SRS) planning practices between five international institutions, all member of the Elekta Spine Radiosurgery Research Consortium
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