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MRI-Based Post Dosimetry for Prostate Seed Implant

J Li

J Li*, M Lin, L Chen, C Ma, Fox Chase Cancer Center, Philadelphia, PA

SU-E-T-352 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To investigate the feasibility of using the MR images only for the post dosimetry evaluation of transrectal-ultrasound-guided prostate seed implant.

Methods: Post dosimetry evaluation for prostate seed implant is important to ensure the target dose coverage and the normal tissue sparing. CT is primarily used for this procedure and MR image is used in some institutions for target delineation because of its advantages on soft tissue discrimination. It will reduce the cost and increase the efficiency and the accuracy as well to use the MR images alone for the post dosimetry. The barrier for performing MRI based post dosimetry is the accuracy of seed finding. Ten patients with both CT and MR images were recruited for this study. The seeds were found manually based on the MR images only and compared with the CT-based seed finding for every patient. The dose parameters calculated based on the found seeds were compared.

Results: Iodine-125 seed were used for the implant and the average seed number is 77 for the selected patients. About 92% of the seeds found on the MR images are confirmed by the CT images. The standard deviation of the confirmation rate is 2.9%. The dose parameter V100 and D90 of the target were compared based on the seeds found on MR and CT images. The difference on V100 is 0% with a standard deviation of 4%. The difference on D90 is 2.7% on average with a standard deviation of 11%.

Conclusion: Most of the seeds can be found on MR images accurately and the MRI-based post dosimetry is feasible as proven by the V100 that has no significant difference comparing with the CT-based dosimetry. Efforts on MR imaging could improve the accuracy of seed detecting and the radioactive seed with MRI marker could fundamentally solve the problem.

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