Development and QA of a Novel Framework to Quantify Normal Tissue Toxicity Using the Jacobian Map
J Niedzielski*, J Yang, L Zhang, M Martel, T Briere, D Gomez, L Court, MD Anderson Cancer Center, Houston, TXTU-G-108-7 Tuesday 4:30PM - 6:00PM Room: 108
Purpose: To develop and validate a novel computational method that quantifies the dose-response of tissues on a voxel-to-voxel level.
Methods: An algorithm was created to calculate the Jacobian Map (JM) from the deformation computed between a planning CT image and treatment image. This Jacobian Map represents local volume change at the voxel level. The relationship between the JM and the local radiation dose can be used to investigate the dose-response of tissues on a voxel level. To validate the algorithm, a mathematical phantom simulating swelling of known quantities was used. The algorithm was then used to investigate esophageal swelling associated with grade 3 esophagitis for five non-small cell lung cancer patients previously treated with external beam radiotherapy. The JM was calculated for CT images of the first and final week of treatment, deformed from the planning CT image. The JM for the first week is a control to assess patient specific uncertainties in this framework. The mean JM of the final week and dose to the esophagus for each axial slice were analyzed for each patient.
Results: The phantom test showed the accuracy and precision of the algorithm to calculate the JM. The five patients analyzed showed a similar behavior as the phantom: an increasing JM corresponds to increasing dose. Week 1 mean JM values were 0.95-1.1 with standard deviations of 0.08-0.12, indicating no quantifiable swelling. Final week JM values showed a quadratic trend with dose with a mean correlation coefficient of 0.78 (range 0.70-0.85). The amount of expansion was patient dependent (range 40%-200%) and greatest at maximal doses.
Conclusion: The computational framework developed in this study shows viability to quantify esophageal expansion throughout the course of radiotherapy as an objective test for normal tissue toxicity. This method may be applied to other organs as well as tumor response.