Presenter(s)
K. J. Redmond1, S. Enyew2, M. Alonso-Basanta3, V. Gondi4, D. R. Grosshans5, L. M. Halasz6, M. D. Hall7, A. L. Holtzman8, S. Lillo9,10, S. S. Lo6, S. M. MacDonald11, A. Mahajan12, D. Mukherjee13, Y. Yamada14, and A. Sahgal15; 1Department of Radiation Oncology and Molecular Radiation Sciences, Johns Hopkins University, Baltimore, MD, 2Department of Radiation Oncology and Molecular Radiation Sciences, Johns Hopkins University School of Medicine, Baltimore, MD, 3Department of Radiation Oncology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, 4Northwestern University Feinberg School of Medicine, Chicago, IL, 5Division of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, 6Department of Radiation Oncology, University of Washington/Fred Hutchinson Cancer Center, Seattle, WA, 7Miami Cancer Institute, Miami, FL, 8Mayo Clinic, Rochester, MN, 9CNAO National Center for Oncological Hadrontherapy, Pavia, Italy, 10University of Pavia, Pavia, Italy, 11Southwest Florida Proton Center, Estero, FL, 12Johns Hopkins University, Baltimore, MD, 13Department of Neurosurgery, Johns Hopkins University School of Medicine, Baltimore, MD, 14Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, NY, 15Department of Radiation Oncology, Odette Cancer Centre, Sunnybrook Health Sciences Centre, University of Toronto, Toronto, ON, Canada
Purpose/Objective(s):
Base of skull (BOS) chordoma is a rare tumor of the notochordal remnant. Dose escalated radiation therapy plays a critical role in optimizing local control, but rates of local recurrence remain high. Particle therapy centers treating BOS chordoma are becoming more prevalent, yet few detailed radiotherapy guidelines exist. The purpose of this study was to develop consensus guidelines to promote safe, effective treatment of skull base tumors.Materials/Methods:
13 central nervous system specialists from 11 centers in the US, Canada, & Italy completed a 19-question survey about radiotherapy for BOS chordoma. Responses were defined as follows: 1) consensus: selected by =75% of respondents, 2) predominant: selected by =50% of respondents, 3) controversial: <50% agreement between respondents.Results:
Survey respondents report an average of 16 years in practice (range: 3-28 years) and treat of approximately 150 cases/year in aggregate. The majority (69%) of participants use proton therapy while the remainder use IMRT/VMAT (15%), carbon ion (8%) and radiosurgery (8%). Consensus GTV includes gross disease on high resolution pre- and post-operative MRI and coregistered CT. Consensus is to have multiple dose levels for CTV: 1) Consensus for high-risk CTV is to include the tumor bed and gross disease plus 5 mm margin, edited for anatomic boundaries and to include high risk regions based on surgical approach; 2) Low-risk CTV volume is controversial but often involves the entire clivus and involved foramina, bilateral cavernous sinuses or ipsilateral cavernous sinus if lateralized, and regions adjacent to those in direct contact of the tumor. Consensus for low-risk CTV is to carve off the adjacent brainstem. Consensus prescription dose for the high-risk CTV is 70-76 Gy in 1.8-2 Gy/fraction. Prescription dose to the low-risk CTV is controversial, ranging from 56-63 Gy in the same fractionation. Consensus is that the prescription be modified to meet critical normal tissue constraints or for toxicity. The predominant definition of peripheral brainstem is a 3 mm rim around the brainstem. The consensus constraint for the central brainstem is 50-56 Gy. The predominant constraint for the brainstem surface is 63-73 Gy. Cochlea constraint is controversial with tumor coverage often prioritized such that the dose to the ipsilateral cochlea may be exceeded in selected cases.Conclusion:
We present consensus guidelines for BOS chordoma based on a survey of experienced practitioners, which may be used to guide management of skull-based tumors at large. Future investigation will be critical in better understanding areas of controversy including delineation and prescription dose for the low-risk CTV for BOS chordoma.