Quantitative Approach to Intensity-Modulated Radiation Therapy Quality Assurance Based on Film Dosimetry and Optimization

To accurately verify the dose of intensity-modulated radiation therapy (IMRT), we have used a global optimization method to investigate a new dose-verification algorithm. In practical application of this quality assurance (QA) procedure, verification of the dose using calculated and measured dose distributions involves a subtle problem in the region of high dose gradient. Consideration of systematic errors shows that the large dose differences in high-dose-gradient regions are due to the unexpected shift of measuring devices. We have proposed an optimization algorithm to correct this error, and an optimization method to minimize the average dose difference has been used in this study. The relationship between the dose-verification procedure and the applied optimization algorithm is explained precisely. Optimization dramatically reduced the difference between measured and calculated dose distributions in all cases investigated. The obtained results support the relevance of our explanations for the problem in the high-dose-gradient region. We have described this dose-verification procedure for IMRT and intensity-modulated radiosurgery. Through this study we have also developed an intuitive reporting method that is statistically reasonable.