Program Information
Dose Tolerance for SBRT/SABR
J Grimm*, Johns Hopkins University, Baltimore, MD
Presentations
WE-AB-207B-1 (Wednesday, August 3, 2016) 7:30 AM - 9:30 AM Room: 207B
Purpose: Stereotactic body radiation therapy (SBRT) / stereotactic ablative body radiotherapy (SABR) is gaining popularity, but quantitative dose tolerance has still been lacking. To improve this, the April 2016 issue of Seminars in Radiation Oncology will have normal tissue complication probability (NTCP) models for 10 critical structures: optic pathway, cochlea, oral mucosa, esophagus, chestwall, aorta, bronchi, duodenum, small bowel, and spinal cord.
Methods: The project included more than 1500 treatments in 1-5 fractions using CyberKnife, Gamma Knife, or LINAC, with 60 authors from 15 institutions. NTCP models were constructed from the 97 grade 2-3 complications, predominantly scored using the common terminology criteria for adverse events (CTCAEv4). Dose volume histogram (DVH) data from each institutional dataset was loaded into the DVH Evaluator software (DiversiLabs, LLC, Huntingdon Valley, Pa) for modeling. The current state of the literature for the critical structures was depicted using DVH Risk Maps: comparative graphs of dose tolerance limits that can include estimated risk levels, reported complications, DVH data for study patients, as well as high- and low-risk dose tolerance limits.
Results: For relatively acceptable toxicity like grade 1-3 rib fractures and chestwall pain, the high-risk limits have 50% risk and the low-risk limits have 5% risk. Emami et al (IJROBP 1991 May 15;21(1):109-22) used 50% and 5% risk levels for all structures, whereas this effort used clinically acceptable ranges for each: in structures like aorta or spinal cord where complications must be avoided, the high- and low-risk limits have about 3% and 1% risk, respectively, in this issue of Seminars. These statistically based guidelines can help ensure plan quality for each patient.
Conclusion: NTCP for SBRT is now becoming available. Hypofractionated dose tolerance can be dramatically different than extrapolations of conventional fractionation so NTCP analysis of the SBRT/SBRT data is important to ensure safe clinical practice.
Funding Support, Disclosures, and Conflict of Interest: Dr. Grimm, designed and holds intellectual property rights to the DVH Evaluator software tool which is an FDA-cleared product in commercial use, and was used to analyze the data.
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