Permanent prostate brachytherapy postimplant magnetic resonance imaging dosimetry using positive contrast magnetic resonance imaging markers

Abstract

Background/Purpose Permanent prostate brachytherapy dosimetry using CT-MRI fusion combines the anatomic detail of MRI with seed localization on CT, but requires multimodality imaging acquisition and fusion. The purpose of this study was to compare the utility of MRI only post-implant dosimetry to standard CT-MRI fusion based dosimetry. Methods Twenty-three patients undergoing permanent prostate brachytherapy with use of positive contrast MRI markers were included in this study. Dose calculation to the whole prostate, apex, mid-gland, and base was performed via standard CT-MRI fusion and MRI only dosimetry with prostate delineated on the same T2 MRI sequence. The 3-dimensional distances between seed positions of these 2 methods were also evaluated. Wilcoxon matched-pair signed-rank test compared the D90 and V100 of the prostate and its sectors between methods. Results The day zero D90 and V100 for the prostate were 98% vs. 94% and 88% vs. 86% for CT-MRI fusion and MRI only dosimetry. There were no differences in the D90 or V100 of the whole prostate, mid-gland or base between dosimetric methods (p >0.19), but prostate apex D90 was higher 13% with MRI dosimetry (p = 0.034). The average distance between seeds on CT-MRI fusion and MRI alone was 5.5 mm. After additional automated rigid registration of 3D seed positions the average distance between seeds was 0.3 mm, and the previously observed differences in apex dose between methods was eliminated (p>0.11). Conclusion Permanent prostate brachytherapy dosimetry based only on MRI using positive contrast MRI markers is feasible, accurate, and reduces the uncertainties arising from CT-MRI fusion abating the need for post-implant multimodality imaging.

MRI-assisted radiosurgery: A quality assurance nomogram for palladium-103 and iodine-125 prostate brachytherapy

“…One major difference compared with TRUS-planned implants evaluated on postimplant CT is the improved accuracy of prostate delineation and reproducible postimplant dosimetry. Unlike postimplant CT, which is complicated by edema (requiring a second CT at $ 30 days), we have found that differences in dosimetric coverage do not seem to be significant over time for MR-based dosimetry (1,2). Ultimately, coverage (V100 and D90) for Day 0 remained excellent and consistent with high-quality BT.…”

Postimplant Dosimetry of Permanent Prostate Brachytherapy: Comparison of MRI-Only and CT-MRI Fusion-Based Workflows

“…Previous studies on MRI-only postimplant dosimetry using contrast-enhanced T1-weighted images had poor results on the detection of seeds at the boundaries of the prostate and extraprostatic seeds, therefore, were not deemed clinically reliable. 8,26 Frank et al 11 have reported excellent performance of an MRI-only workflow using C4 MR markers with the application of endorectal coil (without any loose or clumped seeds).…”

“…Also, glucagon is commonly administered to prostate patients at many clinics (including the study by Frank et al) before prostate MRI to suppress rectal movements and avoid image distortions. 11 Administration of glucagon to reduce the motion of prostate adjacent structures, including rectum, bladder, and small bowel may be considered. In addition, it is strongly recommended to scan patients with empty rectum for optimal QSM results.…”

“…10 Martin et al have compared the MRI-only LDR postimplant dosimetry (using stranded seeds with cobaltdichloride-N-acetyl cysteine [C4] MR-markers as spacers) to the standard MR-CT fusion-based approach. 11,12 They have demonstrated that MRI-only dosimetry using C4 MR markers is feasible and accurate; however, there are some limitations associated with C4 application such as higher cost compared with conventional seeds, the necessity of endorectal coil for marker visualization, and nonapplicability to plans with nonspaced or loose seeds. 11 It should be considered that in all the aforementioned approaches, the implanted seeds still appear as dark voids, making it challenging to be differentiated from other voids such as calcifications and small blood vessels, especially in the case of extraprostatic seeds.…”

“…11,12 They have demonstrated that MRI-only dosimetry using C4 MR markers is feasible and accurate; however, there are some limitations associated with C4 application such as higher cost compared with conventional seeds, the necessity of endorectal coil for marker visualization, and nonapplicability to plans with nonspaced or loose seeds. 11 It should be considered that in all the aforementioned approaches, the implanted seeds still appear as dark voids, making it challenging to be differentiated from other voids such as calcifications and small blood vessels, especially in the case of extraprostatic seeds. MRI-based positive contrast seed visualization would make it easier for the physicist or the radiation oncologist to review and approve the postplan after running the automated seed finder.…”