Program Information
Use of MR for Permanent Prostate Implant Preplanning
V Narayana1,2*, B Yao1 , P McLaughlin1,2 , (1) Assarian Cancer Center, Novi, MI, (2) University of Michigan, Ann Arbor, MI
Presentations
SU-F-J-167 (Sunday, July 31, 2016) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: To study the feasibility using MR imaging to improve target definition on ultrasound during permanent prostate implants and aid in source strength determination for treatment planning in the OR.
Methods: Patients who receive permanent prostate implants undergo MR and CT imaging prior to the implant procedure to determine the volume of the prostate, bony restriction to the procedure, bladder extension, external sphincter length and neurovascular bundle. The volume of the prostate is generally used to order seeds for the procedure. In 10 patients, the MR was used as the preplanning study with the PTV defined as a 2 mm expansion of the MR prostate in all directions except the posterior. Various dose volume parameters for the MR prostate and the PTV were compared to the actual preplan developed and executed in the OR. In addition, there parameters were compared to the post implant dosimetry performed 3 weeks after the implant procedure.
Results: The results show that the number of seeds used using MR and US (ultrasound) planning was generally with 2 seeds and the maximum difference was 7 seeds. There is no significant difference between any of the dose index parameters of V100, V150, V200, D99 and D90 parameters between MR planning, US planning and postimplant evaluation There was a significant difference between planned D99 (avg of 105%) and achieved D99 (avg 91%).
Conclusion:MR imaging is an invaluable tool to improve target definition for permanent prostate implants. Use of MR images for preplanning improves the confidence with which source can be ordered for the procedure that is OR planned. Ordering a maximum of 10 seeds more than planned would be sufficient to deliver a plan in the OR using US. Moving ahead to non-rigid registration between MR ad US images could further increase the confidence level of MR planning.
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