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Feasibility of MRI-Based Preplan On Low Dose Rate Prostate Brachytherapy

Y Huang

Y Huang*, J Tward , P Rassiah-Szegedi , H Zhao , V Sarkar , L Huang , M Szegedi , K Kokeny , B Salter , University of Utah Huntsman Cancer Institute, Salt Lake City, UT


SU-E-J-232 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall

To investigate the feasibility of using MRI-based preplan for low dose rate prostate brachytherapy.

12 patients who received transrectal ultrasound (TRUS) guided prostate brachytherapy with Pd-103 were retrospectively studied. Our care-standard of the TRUS-based preplan served as the control. One or more prostate T2-weighted wide and/or narrow-field of view MRIs obtained within the 3 months prior to the implant were imported into the MIM Symphony software v6.3 (MIM Software Inc., Cleveland, OH) for each patient. In total, 37 MRI preplans (10 different image sequences with average thickness of 4.8mm) were generated. The contoured prostate volume and the seed counts required to achieve adequate dosimetric coverage from TRUS and MRI preplans were compared for each patient. The effects of different MRI sequences and image thicknesses were also investigated statistically using Student’s t-test. Lastly, the nomogram from the MRI preplan and TRUS preplan from our historical treatment data were compared.

The average prostate volume contoured on the TRUS and MRI were 26.6cc (range: 12.6~41.3cc), and 27.4 cc (range: 14.3~50.0cc), respectively. Axial MRI thicknesses (range: 3.5~8.1mm) did not significantly affect the contoured volume or the number of seeds required on the preplan (R2 = 0.0002 and 0.0012, respectively). Four of the MRI sequences (AX-T2, AX-T2-Whole-Pelvis, AX-T2-FSE, and AXIAL-T2-Hi-Res) showed statistically significant better prostate volume agreement with TRUS than the other seven sequences (P <0.01). Nomogram overlay between the MRI and TRUS preplans showed good agreement; indicating volumes contoured on MRI preplan scan reliably predict how many seeds are needed for implant.

Although MRI does not allow for determination of the actual implant geometry, it can give reliable volumes for seed ordering purposes. Our future work will investigate if MRI is sufficient to reliably replace TRUS preplanning in patients where preplan TRUS may be technically challenging.

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