Central Nervous System

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MO_2_2503 - Consensus Guidelines for Target Volume Definition of the Sacrum in Spinal Stereotactic Body Radiation Therapy (SBRT)

Monday, October 22
10:45 AM - 12:15 PM
Location: Innovation Hub, Exhibit Hall 3

Consensus Guidelines for Target Volume Definition of the Sacrum in Spinal Stereotactic Body Radiation Therapy (SBRT)
E. M. Dunne1, A. Sahgal2, S. S. Lo3, A. Bergman1, R. Kosztyla1, E. L. Chang4, U. Chang5, S. T. Chao6, A. J. Ghia7, K. J. Redmond8, S. G. Soltys9, S. Faruqi2, and M. C. Liu1; 1Department of Radiation Oncology, BC Cancer - Vancouver Centre, Vancouver, BC, Canada, 2Department of Radiation Oncology, Sunnybrook Odette Cancer Centre, University of Toronto, Toronto, ON, Canada, 3University of Washington, Department of Radiation Oncology, Seattle, WA, 4University of Southern California Keck School of Medicine, Los Angeles, CA, 5Korea Institute of Radiological & Medical Sciences, Seoul, Korea, Republic of (South), 6Department of Radiation Oncology, Taussig Cancer Center, Cleveland Clinic, Cleveland, OH, 7Dept. of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, 8Department of Radiation Oncology and Molecular Radiation Sciences, Johns Hopkins University School of Medicine, Baltimore, MD, 9Department of Radiation Oncology, Stanford Cancer Institute, Stanford, CA

Purpose/Objective(s): To develop consensus contouring guidelines for spinal stereotactic body radiation therapy (SBRT) for metastatic disease to the sacrum to improve uniformity in clinical target volume (CTV) delineation.

Materials/Methods: Nine radiation oncologists with spinal stereotactic radiotherapy expertise representing 9 international centres in 3 countries independently contoured gross tumour volume (GTV), CTV and neural elements (cauda equina, thecal sac or sacral canal) for 10 representative clinical scenarios in metastatic disease to the sacrum. Contours were imported into an in-house software program, and agreement between physicians calculated with an expectation minimization algorithm using simultaneous truth and performance level estimation (STAPLE) and with kappa statistics (<0, poor agreement; 0.01-0.20, slight agreement; 0.21-0.40, fair agreement; 0.41-0.60, moderate agreement; 0.61-0.80, substantial agreement; 0.81-1.00, almost perfect agreement). Optimized confidence level consensus contours were obtained using a voxel-wise maximum likelihood approach. Clinicians also completed an 18-question survey about sacral metastatic disease SBRT practice including dose/fractionation schedule, margin expansion for GTV to CTV and CTV to planning target volume (PTV), the practice of contouring the sacral plexus and/or peripheral nerve roots and acceptable dose constraints for neural elements and small/large bowel.

Results: The mean STAPLE agreement sensitivity and specificity was 0.73 (range, 0.59-0.86) and 1.00 respectively for GTV and 0.59 (range, 0.47-0.69) and 1.00, respectively for CTV. The mean kappa agreement was 0.76 (range, 0.60-0.89) for GTV and 0.60 (range, 0.45-0.72) for CTV (P<.001 for GTV and CTV in all cases). Different dose/fractionation schedules used included 16-24 Gy/1 fraction, 24 Gy/2 fractions, 24-27 Gy/3 fractions, 30-36 Gy/4 fractions and 35 Gy/5 fractions, primary histology of the tumour was a factor in certain cases when choosing a schedule. Six experts applied an anatomic approach to the CTV, in some cases adding an extra margin for soft tissue extension/extra-osseous disease. Median PTV expansion was 1 mm (range, 0 – 3 mm). Six experts contoured the thecal sac as a surrogate for the cauda equina. In the majority of cases the sacral plexus and peripheral nerves were contoured however the lack of consensus contouring guidelines and low rates of clinical plexopathy observed in practice were reasons why contouring these critical normal structures wasn’t universal practice.

Conclusion: There was substantial agreement for GTV and moderate agreement for CTV contours with the majority of international experts applying an anatomic approach when contouring the CTV. Final consensus guidelines will be demonstrated in illustrations at the meeting.

Author Disclosure: E.M. Dunne: None. A. Sahgal: Research Grant; Elekta AB. Honoraria; Elekta AB, Varian. Travel Expenses; Elekta AB. Ex Officio; International Society of Stereotactic Radiosurgery. AO Spine Tumor Forum committee member; AO Spine. S.S. Lo: Chair; American College of Radiology. Radiation Oncology Track Chair; Radiological Society of North America (RSNA). R. Kosztyla: Vice President; BC Association of Medical Physicists. E.L. Chang: Honoraria; Brainlab. Track Member; ASCO. U. Chang: President; Korea Spinal Oncology Research Society. S.T. Chao: Honoraria; Varian Medical Systems, Zeiss, Abbvie. Consultant; Abbvie. A.J. Ghia: None. K.J. Redmond: Research Grant; Elekta AB, Accuray. Honoraria; AstraZeneca, Accuray. Travel Expenses; Elekta AB, Accuray. S.G. Soltys: Consultant; Inovio Pharmaceuticals, Inc. M. Liu: None.

Emma Dunne, PhD, MBBS, FRCR

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