Evaluating Published Skin Dose Tolerance Limits for Stereotactic Body Radiation Therapy of Lung Cancer

Objectives: Published local control rates for certain stereotactic body radiotherapy (SBRT) lung cancer treatments have exceeded 97%, but several serious adverse events have been reported. No five-year normal tissue complication probability (NTCP) statistical analysis SBRT results have been published yet for skin. While we expectantly await these publications, the goal of this manuscript is to glean the published expert opinion and ongoing clinical trials for skin dose tolerance limits in one to five fractions for clinical application and research. Methods: All 42 lung tumors treated with the CyberKnife at Cooper University Hospital from July 2008 to May 2010 that had skin contours and Monte Carlo dose calculations with heterogeneity corrections were reviewed for toxicity. Twenty-one published dose tolerance limits for skin were partitioned into high-risk and low-risk categories. The DVH Evaluator software tool was developed by the first author and used to conveniently assess the dose tolerance limits for each case prior to treatment and to analyze the followup data. Results: Three of the 42 patients experienced mild Grade 1 erythema that resolved within a few months. No Grade 2 or higher adverse events of skin toxicity were encountered. A unified framework of high-risk and low-risk skin dose limits in one to five fractions at specific dose-volume levels is presented. Conclusions: When the dose tolerance limits are diligently studied and respected, SBRT has potential to be a safe and effective form of radiation therapy. Longer follow-up will still be required to statistically analyze late effects and long-term outcomes.