Room: ePoster Forums
Purpose: Image-guidance has been widely used in the clinic for accurate radiotherapy. However, a practical and effective method to evaluate the effect of image-guidance in the radiotherapeutic management of cancers is absent. 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 metric termed image-guidance index (IGI), has been 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 to the square sum of dose summation between the two matrixes, summing over all dose scoring voxels. Ranging from 0 to 1, larger IGI values indicate larger benefit out of image-guidance. An in-house MATLAB code with matrix operation was developed for the calculation of IGI. With IRB approval, IGI values were calculated based on the DICOM RT files of 675 head and neck cancer patients treated with various IGRT techniques. Finally, the IGI values were calculated and compared among the various site groups and various techniques of 3DCRT, IMRT and VMAT.
Results: Overall, IGI increases monotonously as shift increases, with different slopes among various directions and various groups. For intracranial tumor, the ratios of the medians of IGI among VMAT, IMRT and 3DCRT were 0.45:0.60:1.00 in AP direction, 0.63:0.89:1.00 in RL direction, and 0.83:0.58:1.00 in SI direction, respectively. The differences in the median values of IGI among different directions are greater than would be expected by chance for whole brain with 3DCRT, intracranial site with VMAT and IMRT, clavicle with 3DCRT (P<0.001).
Conclusion: IGI values vary significantly among various cancer types and IGRT techniques. Our results indicate that IGI can be used as an effective tool to quantify the benefit of image guidance in IGRT.
Funding Support, Disclosures, and Conflict of Interest: Funding support from Sichuan University.
Not Applicable / None Entered.