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Assessment of Bone Electron Density Effects On Dose Calculation and Optimization Accuracy for MRI-Only Treatment Planning for Cervical Carcinoma in 1.5 T MR-Linac

S Ding1,2*, H Liu1,2, Y Li1,2, B Wang1,2, B Liu1,2, X Qi1,2, X Cao1,2, X HUANG1,2, (1) Sun Yat-sen University Cancer Center, Guangzhou,CN, (2) State Key Laboratory of Oncology in South China,Guangzhou,CN


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

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.

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Funding Support, Disclosures, and Conflict of Interest: National Natural Science Foundation of China (No. 11805292); Natural Science Foundation of Guangdong, China (No. 2018A0303100020)


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