Evaluation of the heterogeneity corrections impact in lung stereotatic body radiation therapy

Abstract

Stereotactic body radiation therapy (SBRT) refers to an emerging radiotherapy that is highly effective in controlling early primary and oligometastic cancers at locations throughout the abdominopelvic and thoracic cavities, and at spinal and paraspinal sites. Some protocols have been developed for this procedure. In the special cases of lung, there are protocols in use that consider heterogeneity corrections and others that do not make use of heterogeneity correction. In this work, we recalculated, considering the different tissue densities plans initially optimized without heterogeneity corrections to evaluate the dosimetric changes that occurs, for example, PTV (planning target volume) coverage, dose to isocenter and dose to critical structures, and we calculated gamma function between the dose plans originated in the two conditions. We also performed the superposition between the calculated gamma function with the respective CT slice in order to evaluate in what conditions occur the major differences between the conditions of calculus considered. The results showed that relevant variations occur between the two situations of calculus. With the superposition of the image relative to γ index and its respective CT slice, we could visualize where the greatest discrepancies occur. These data allow us to evaluate with more accuracy the doses delivered to the target and organs at risk and compare different protocols, independently of the use or non-use of heterogeneity corrections.