Lyman-Kutcher-Burmanp Pelvic Radiation Dosimetric Prediction Model of Acute Hematologic Toxicity for Rectal Cancer Patients

Abstract

head) to 1.11 (rectum) for the composite plan and from 1.00 to 1.27 for individual treatment beams. For the thorax, estimates of the tumor RBE ranged from 1.05 to 1.06; composite plan RBE estimates for OARs (heart, lungs, spinal cord, esophagus, breast, brachial plexus) ranged from 1.02 (breast) to 1.2 (spinal cord). Biological hot spots (RBE up to 1.27) were noted to arise near the distal edge of the Bragg peak. Conclusion: Patient-and tumor-specific RBE estimates from a model that accounts for spatial variations in LET are within +5% of a constant clinical RBE of 1.1. Estimates of the RBE among patients can differ from 1.1 by as much at 15% (RBE w 1.0 to 1.3) for some OAR. The OAR RBE values for individual beams can differ substantially from the RBE for the composite plan, which suggests that beam by beam optimization of (variable RBE x dose) might be exploited to reduce treatment complications (reduce the OAR RBE from w 1.3 to 1.0). This could potentially allow room to increase the therapeutic ratio by 10% to 20% of the total treatment dose.