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Quantification of Image-Guidance Benefit in Image-Guided Radiotherapy of Cancers

L Zhou

L Zhou1,2*, J Deng2 , (1) Division of Radiation Physics, State Key Laboratory of Biotherapy and Cancer Center, West China Hospital, Sichuan University, Chengdu 610041, China(2) Department of Therapeutic Radiology, Yale University, New Haven, CT


SU-F-J-209 (Sunday, July 31, 2016) 3:00 PM - 6:00 PM Room: Exhibit Hall

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.

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