Room: AAPM ePoster Library
Purpose: assess the impact of undelinated bone regions on dose calculation and optimization results of MRI-only based cervical IMRT plans.
Methods: retrospective cervix patients who were treated on the 1.5T MR-Linac with their original CT and MRI datasets were used. All the plans were created using TPS Monaco 5.40. The synthetic CT (s-CT) for MRI was generated using bulk ED assignment according to the mean ED values of the delineated structures. Another set of s-CT was generated with fully delineation of all the bone regions to investigate the dosimetric impact. The adaptive plans for the two s-CT sets,were created by copying from the original CT and recalculating, which denote as “BoneRC-MRI” and “NoBoneRC-MRI”.The above s-CT based adaptive plans were copied and reoptimized to evaluate the influence of optimization process, which denote as “BoneRO-MRI” and “NoBoneRO-MRI”.All the adaptive plans were recalculated on the original CT for comparison. DVH parameters (DVPs) and Gamma analysis were implemented for assessment.
Results: comparison of the recalculation plans on two s-CT sets, NoBoneRC-MRI plans significantly increase PTV dose. Comparing the recalculation plans on original CT and s-CT, the result showed that the BoneRC-MRI plans lead to smaller dose effect than NoBoneRC-MRI by comparing RC-CT. And gamma pass rate (GPR) of BoneRC-MRI was higher than NoBoneRC-MRI. Additionally, comparing the reoptimized plans on two s-CT sets, the DVPs were no significantly difference. However in comparison of reoptimized plans on original CT and s-CT, the result showed that the BoneRO-MRI plans also lead to smaller dose effect than NoBoneRO-MRI by comparing BoneRO-CT and NoBoneRO-CT. And the GPR of BoneRO-MRI was more higher than NoBoneRO-MRI.
Conclusion: commonly used bulk ED assignment with part of bone delineation is not sufficient for cervical cancer MRI-only planning. Fully delineation of the bones has the potential to reduce the error of s-CT generation.
Funding Support, Disclosures, and Conflict of Interest: National Natural Science Foundation of China (No. 11805292); Natural Science Foundation of Guangdong, China (No. 2018A0303100020)