Validation of radiation treatment planning with a pseudo-CT derived from MR images

Abstract

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT REQUEST OF AUTHOR.] Historically CT has been the necessary for radiation therapy dose calculation due to its inherent density information. However there is increased interest in using solely MR for treatment planning. This study describes the DRR generation and evaluates the accuracy of dose calculation for radiation oncology planning using pseudo-CT created solely from MRI. Four types of data sets were created for each of seven patients for dose comparison. 1) The regular CT, 2) the pseudo-CT created from MRI, 3) T2 image for bulk density assignment and 4) the same CT image as above with a homogenous density assigned. 3D and VMAT plans were generated for each image set using the regular CT (reference image) in a commercial planning system. The plan was then transferred onto the three other methods (pseudo-CT, bulk density assignment and homogenous), and the dose was recalculated by keeping the same field parameters and monitor units. Dose point calculation and gamma index was used to access the dose accuracy. The point dose calculation agreement and the percentage of points passing the gamma index are excellent for the pseudo-CT and bulk methods with very minimal difference compared to the reference CT. The dose calculation for bulk density method is considered precise in the literature but very labor intensive and not clinical feasible. This work shows the accuracy of dose calculation with pseudo-CT is as precise as assigned bulk density method and is much easier to implement into clinical practice.