SU‐F‐J‐209: Quantification of Image‐Guidance Benefit in Image‐Guided Radiotherapy of Cancers

Abstract

Purpose:Image‐guidance has been widely used in radiation oncology for accurate radiotherapy. The goal of this study is to quantify the benefit of image‐guidance in image‐guided radiotherapy (IGRT) of cancers.Methods:In this study, a new index termed image‐guidance benefit (IGB), was proposed to quantify the benefit of image‐guidance in cancer radiotherapy. It is calculated as a ratio of the square sum of dose differences between planning dose matrix and actual delivery dose matrix post image‐guidance to the square sum of dose summation between the two matrixes, summing over all dose scoring voxels. Ranging from 0 to 1, larger IGB values indicate larger benefit out of image‐guidance. With IRB approval, the DICOM RT files and 3D couch shifts applied during IGRT of 2219 patients were collected, based on which patient‐specific IGB values were calculated with an in‐house MATLAB code.Results:In this study, the mean IGB value was found to be 0.0398 (0.000583–0.999) with a positive correlation between IGB value and 3D couch shift vector at 0.0435 per cm (P<0.0001). With 2 mm shift as a threshold above which an image‐guidance is deemed clinically necessary, the corresponding mean IGB value was 0.00457, much less than 0.0398 (P<0.001). However, the IGB values of 56 cases based on couch shifts were less than those based on 2 mm shift.Conclusion:The IGB values were patient‐specific and site‐dependent. Using 2 mm shifts as criterion for applying image‐guidance, the applied image‐guidance procedures were found clinically necessary and highly beneficial in 97.5% of cancer patients. However, image‐guidance procedures were found over‐used in about 2.5% of cancer patients in our current practices of IGRT, which should be avoided as they added no benefit in improving delivery accuracy while increasing cancer risk.