Comparison of multiparametric MRI-based and transrectal ultrasound-based preplans with intraoperative ultrasound-based planning for low dose rate interstitial prostate seed implantation

Abstract

Purpose: Transrectal ultrasound images are routinely acquired for low dose rate (LDR) prostate brachytherapy dosimetric preplanning (pTRUS), although diagnostic multiparametric magnetic resonance imaging (mpMRI) may serve this purpose as well. We compared the predictive abilities of TRUS vs MRI relative to intraoperative TRUS (iTRUS) to assess the role of mpMRI in brachytherapy preplanning.

Materials and methods: Retrospective analysis was performed on 32 patients who underwent iTRUS-guided prostate LDR brachytherapy as either mono- or combination therapy. 56.3% had pTRUS-only volume studies and 43.7% had both 3T-mpMRI and pTRUS preplanning. MRI was used for preplanning and its image fusion with iTRUS was also used for intraoperative guidance of seed placement. Differences in gland volume, seed number, and activity and procedure time were examined, as well as the identification of lesions suspicious for tumor foci. Pearson correlation coefficient and Fisher's Z test were used to estimate associations between continuous measures.

Results: There was good correlation of planning volumes between iTRUS and either pTRUS or MRI (r = 0.89, r = 0.77), not impacted by the addition of hormonal therapy (P = 0.65, P = 0.33). Both consistently predicted intraoperative seed number (r = 0.87, r = 0.86). MRI/TRUS fusion did not significantly increase surgical or anesthesia time (P = 0.10, P = 0.46). mpMRI revealed suspicious focal lesions in 11 of 14 cases not visible on pTRUS, that when correlated with histopathology, were incorporated into the plan.

Conclusions: Relative to pTRUS, MRI yielded reliable preplanning measures, supporting the role of MRI-only LDR treatment planning. mpMRI carries numerous diagnostic, staging and preplanning advantages that facilitate better patient selection and delivery of novel dose escalation and targeted therapy, with no additional surgical or anesthesia time. Prospective studies assessing its impact on treatment planning and delivery can serve to establish mpMRI as the standard of care in LDR prostate brachytherapy planning.

Keywords: LDR; MRI; TRUS; brachytherapy; multiparametric; prostate.

Figure 1

Pearson product‐moment correlation coefficient of iTRUS‐based prostate volume with pTRUS (r = 0.89) and mpMRI (r = 0.77).

Figure 2

Targeted dose escalation of mpMRI‐identified PIRADS 5 lesion. Left: Preplan on T2 MRI sequence. Right: Intraoperative MRI/iTRUS fusion for real‐time planning. Contours: Royal blue, prostate; Red, PTV expansion; Yellow, Urethra; Magenta/Yellow arrow, PIRADS 5 lesion; Light blue, hydrogel spacer between prostate and rectum. Isodose lines: Green, 100% of prescription; Orange, 150%; Maroon, 200%.

Figure 3

Pearson product‐moment correlation coefficient of iTRUS‐based predicted seed quantity with pTRUS (r = 0.87) and mpMRI (r = 0.86).

Figure 4

Pearson product‐moment correlation coefficient of intraoperative real‐time prostate volume (cc) with postoperative volume (r = 0.98).