In-bore MRI targeted biopsy

Abstract

Clinical suspicion of Prostate Cancer (PCa) is largely based on increased prostate specific antigen (PSA) level and/or abnormal digital rectal examination (DRE) and/or positive imaging and, up today, biopsy is mandatory to confirm the diagnosis. The old model consisted of Standard Biopsy (SBx), that is random sampling of the prostate gland under ultrasound guidance (TRUS), in subjects with clinical suspicion of PCa. This involves the risk of not diagnosing a high percentage of tumors (up to 30%) and of an incorrect risk stratification. Multiparametric Magnetic Resonance Imaging (mpMRI) has transformed the diagnostic pathway of PCa, not only as an imaging method for detecting suspicious lesions, but also as an intraprocedural guidance for Target Biopsy (MRI-TBx), thus bridging the diagnostic gap. Several single and multicenter randomized trials, such as PROMIS, MRI first, PRECISION and that reported by Van der Leest et al. have confirmed the superiority of the "MRI pathway", consisting of mpMRI and MRI-TBx of suspicious lesions, over the "standard pathway" of SBx in all patients with elevated PSA and/or positive DRE. MRI-TBx appears to be advantageous in reducing the overall number of biopsies performed, as well as in reducing the diagnosis of clinically insignificant disease while maintaining or improving the diagnosis of clinically significant PCa (cs-PCa). Moreover, it shows a reduction in the diagnosis of ins-PCa, and therefore, of overdiagnosis, when using MRI-TBx without sacrificing performance in the diagnosis of cs-PCa.

Fig. 1.

“Manual System for In-Bore MRI-TBx” – Insertion of introducer in rectum of patient in prone position (A); Device movement determined by applying two rotations and longitudinal translation (B); Axial (C) and para-sagittal (D) T2 weighted (T2W) images are obtained for initial guidance. These images were sent to a dedicated planning workstation where the radiologist identifies the current needle guide position and the target lesion. The software then calculates the adjustments needed to reposition the needle guide such that the needle trajectory arrives at the target lesion.

Fig. 2.

“Manual adjustment of needle trajectory” - Manual in-bore MRI-TBx performed in Patient with the target lesion located on the base of the right Peripheral Zone (PZ) of the gland. Note the needle guide pointing at the suspicious lesion and, from left (A) to right (B), with fine manual adjustments, it has been possible to sample the most suspicion area of the lesion.

Fig. 3.

“In-bore Robotic System” – A. Robotic arm; B. The same initial planning images are obtained and sent to the dedicated workstation where the radiologist indicates the needle guide and target lesion locations. On command from the radiologist, the robot then repositioned the needle guide to point in the direction of the lesion.

Fig. 4.

“Robotic adjustment of needle trajectory” – The software automatically simulated the predicted needle position and overlaid this on the images, providing an estimate of position of the sampling part of the needle relative to the lesion without having to insert the needle. After the movement of the robot, further images are acquired to check if the projection of the sampling part of the needle is correctly positioned within the lesion (totally or at least in part) (A, B). If the predicted needle position did not correspond to the lesion, the radiologist could repeat the above procedure of target definition and repositioning of the needle guide until an acceptable correspondence was reached

Clinical Case 1.

70-year-old man, with PSA 9.2 ng/mL, negative DRE and Atypical Small Acinar Proliferation (ASAP) finding at TRUS-SBx in 1/14 cores. At pre-biopsy mpMRI a 4 mm lesion, with a Prostate Imaging Recording and Data System (PI RADS) score of 4, was found in the left PZ, characterized by circumscribed hypointensity <15mm on T2W sequence (A), focal markedly <15mm hypointensity on Appearent Diffusion Coefficent (ADC) map/ hyperintensity on Diffusion Weight Images (DWI) high b-value image (B, D) and no focal early enhancement (C). An in-bore MRI-TBx was performed: the first core was acquired near the lesion, with pathological next result of normal parenchyma (E); after manual adjustment, the second core was acquired directly into the target, with the following pathological result of 70% of Adenocarcinoma, Gleason Score (GS) 3+4 (F, G).

Clinical Case 2.

65 years old man, with PSA 3.2 ng/mL steadily increasing, negative DRE and no previous biopsy; at pre-biopsy mpMRI a 5mm PI RADS 4 lesion was found in the right anterior PZ, with circumscribed hypointensity <15mm on T2 (A), focal markedly <15mm hypointensity on ADC map/hyperintensity on DWI (B, D) and focal early enhancement (C). During pre-biopsy MRI, the lesion was firstly identified on ADC map and axial T2W plan (E, F), then reached by the needle (G, H), with a final diagnosis of GS 4+3. Final histology after prostatectomy disclosed a pT3aN0 stage and confirmed the GS 4+3 (I, L).

Clinical Case 3.

70 years old man, with PSA 7.98 ng/mL, negative DRE and diagnosis of GS 3+3 in 3/14 at SBx, suitable to Active Surveillance (AS, <20% +ve cores, <50% core involvement, GS 3+3, PSA <10ng/mL, cT1c) [6]; at pre-biopsy mpMRI a 15mm PI RADS 5 lesion was found in the right Central Zone (CZ), with circumscribed hypointensity > 15mm on T2W images(A), focal markedly > 15mm hypointensity on ADC map/hyperintensity on DWI (B, D) and focal early enhancement (C), with suspicious seminal vesicle infiltration. After discussion of the case at multidisciplinary team, a MRI-TBx was perfomed (E), resulting in a GS 4+3 and thus fitting the patient for surgery, with a final staging of pT3b N0 M0.