International Multi-institutional Patterns of Contouring Practice and Clinical Target Volume Recommendations for Stereotactic Body Radiation Therapy for Non-Spine Bone Metastases
Nguyen, Timothy K; Chin, Lee; Sahgal, Arjun; Dagan, Roi; Eppinga, Wietse; Guckenberger, Matthias; Kim, Jin Ho; Lo, Simon S; Redmond, Kristin J; Siva, Shankar; Stish, Bradley J; Chan, Rachel; Lawrence, Liam; Lau, Angus; Tseng, Chia-Lin
(2022) International Journal of Radiation Oncology Biology Physics, volume 112, issue 2, pp. 351 - 360
(Article)
Abstract
PURPOSE: Despite the increasing use of stereotactic body radiation therapy for non-spine bone metastases (NSBM), there is no established standard for target delineation. The objective of this study was to provide consensus recommendations on clinical target volume (CTV) delineation based on international expert contours. METHODS AND MATERIALS: Eleven cases of
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NSBM were contoured by 9 international radiation oncologists. For each case, the gross tumor volume was provided on the simulation computed tomography scans with accompanying magnetic resonance imaging. Participants contoured the CTV and completed a clinical survey. Agreement between CTV contours were analyzed with simultaneous truth and performance level estimation using the kappa coefficient and the Dice similarity coefficient (DSC) and summarized to establish contouring recommendations. A direction-dependent analysis was applied to the consensus contours to quantify margins. RESULTS: All CTV contours were completed. Six participants used a single-dose level, whereas 3 used a 2-dose level simultaneous integrated boost (SIB) technique. For the SIB cases, the largest volume receiving a stereotactic body radiation therapy (SBRT) dose was used for contour analysis. There was substantial agreement between contours across cases with a mean kappa of 0.72 (mean sensitivity 0.85, mean specificity 0.97). The mean DSC value was 0.77 (range, 0.67-0.87). Consensus CTV contouring recommendations were (1) an intraosseous CTV margin of 5 to 10 mm should be strongly considered within contiguous bone; (2) an extraosseous margin of 5 to 10 mm should be strongly considered where there is soft tissue disease or cortical bone disruption; (3) CTVs should be manually cropped to respect anatomic barriers to spread (eg, peritoneal cavity, pleura, uninvolved joint space and cortical bone). CONCLUSIONS: CTV contouring recommendations for NSBM-SBRT were established based on analysis of international expert consensus contours with a high level of agreement. These principles may provide guidance to treating physicians and inform future study until prospective clinical data can provide further refinement.
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Keywords: Radiation, Oncology, Radiology Nuclear Medicine and imaging, Cancer Research, Journal Article
ISSN: 0360-3016
Publisher: Elsevier Inc.
Note: Funding Information: The authors thank Dr Lucas Basler and Dr Minsun Kim for their contributions to this project. Disclosures: R.D. reports personal fees from Elekta and UptoDate outside the submitted work. W.E. reports personal fees from Elekta outside the submitted work. S.S.L. reports being a member of Elekta Gamma Knife ICON Expert Group, outside the submitted work. K.J.R. reports grants and personal fees from Accuray and Elekta and personal fees from BioMimetix and Brainlab outside the submitted work. S.S. reports grants from Varian Industries and Merck-Sharp-Dohme; grants, personal fees, and other from Astra Zeneca; and personal fees from Bristol Meyer Squibb, Astellas, Janssen, and Roche, outside the submitted work. A.S. has been an advisor/consultant with Abbvie, Merck, Roche, Varian (Medical Advisory Group), and Elekta (Gamma Knife Icon); an ex officio board member to International Stereotactic Radiosurgery Society; an honorarium for past educational seminars with Elekta AB, Accuray Inc, Varian (CNS Teaching Faculty), BrainLAB, and Medtronic Kyphon; a research grant from Elekta AB; and travel accommodations/expenses provided by Elekta, Varian, and BrainLAB. A.S. also belongs to the Elekta MR Linac Research Consortium, Elekta Spine, Oligometastases and Linac Based SRS Consortia. C-L.T. reports travel expense/accommodations and honoraria for past educational seminars for Elekta outside the submitted work, and has been a member of the Elekta MR-Linac Research Consortium. Funding Information: There is practice heterogeneity regarding the use of a CTV margin for bone SBRT. Although all participants in the present study advocated for a CTV margin beyond the GTV, there are active and completed clinical trials comparing cEBRT and SBRT for bone metastases with protocols that exclude a CTV margin. 25 , 26 Conversely, patients receiving SBRT on the VERTICAL trial were planned using an isotropic 1.5 cm CTV expansion within bone for both spine metastases and NSBM. Completed oligometastatic trials that included patients who received bone SBRT also show considerable variability. For example, in SABR-COMET no CTV margins were used, 13 whereas the BR-001 trial protocol specified the use of a manually adjusted, nonisotropic planning tumor volume (PTV) margin for spinal lesions that essentially served as a combined CTV and PTV. 27 In the oligometastatic lung cancer trial from Gomez et al, decisions regarding CTV margins were left to the discretion of the treating radiation oncologist. 14 Given the wide variability across studies, it further underscores the importance of establishing reasonable NSBM CTV recommendations to provide consistency in clinical practice and trial design. For spine SRBT, generating a CTV expansion beyond the GTV is supported by consensus guidelines from the International Spine Radiosurgery Consortium, wherein all participants provided unanimous support for this practice. 20 These recommendations stipulate that the CTV should include anatomic bony segments adjacent to the gross disease to reduce the risk of marginal failure from subclinical disease. 28 CTV consensus recommendations for delivering SBRT to sacral metastases are also available and similar to the International Spine Radiosurgery Consortium report, the authors advise the CTV to include uninvolved bony segments that are adjacent to the gross disease. 29 Publisher Copyright: © 2021 Elsevier Inc.
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