Validity of Current Stereotactic Body Radiation Therapy Dose Constraints for Aorta and Major Vessels

Understanding dose constraints for critical structures in stereotactic body radiation therapy (SBRT) is essential to generate a plan for optimal efficacy and safety. Published dose constraints are derived by a variety of methods, including crude statistics, actuarial analysis, modeling, and simple biologically effective dose (BED) conversion. Many dose constraints reported in the literature are not consistent with each other, secondary to differences in clinical and dosimetric parameters. Application of a dose constraint without discriminating the variation of all the factors involved may result in suboptimal treatment. This issue of Seminars in Radiation Oncology validates dose tolerance limits for 10 critical anatomic structures based on dose response modeling of clinical outcomes data to include detailed dose-volume metrics. This article presents a logistic dose-response model for aorta and major vessels based on 238 cases from the literature in addition to 387 cases from MD Anderson Cancer Center at Cooper University Hospital, for a total of 625 cases. The Radiation Therapy Oncology Group (RTOG) 0813 dose-tolerance limit of Dmax = 52.5Gy in 5 fractions was found to have a 1.2% risk of grade 3-5 toxicity, and the Timmerman 2008 limit of Dmax = 45Gy in 3 fractions had 2.3% risk. From the model, the 1% and 2% risk levels for D4cc, D1cc, and D0.5cc are also provided in 1-5 fractions, in the form of a dose-volume histogram (DVH) Risk Map.