Multiparametric MRI before and after Focal Therapy for Prostate Cancer: Pearls and Pitfalls for the Reporting Radiologist

Abstract

In this era of personalized precision medicine, the accuracy of multiparametric MRI (mpMRI) and targeted biopsy in helping detect low-volume clinically significant prostate cancer has rekindled interest in focal therapy for primary prostate cancer. Such therapy may reduce the debilitating morbidity of radical whole-gland treatment. Post-focal therapy mpMRI surveillance is critical for assessing oncologic efficacy. Radiologists interpreting post-focal therapy mpMRI must be familiar with expected posttreatment changes and pitfalls in assessing posttreatment recurrence. In this review, the authors present their experience with mpMRI before and after focal therapy. While cryotherapy and irreversible electroporation are the primary modalities of focal therapy offered in their institution, the authors aim to provide a comprehensive overview of the more common focal therapy modalities in use. Pertinent considerations of mpMRI in pretreatment patient selection and treatment planning are discussed. The recently proposed standardized post-focal therapy assessment systems, Prostate Imaging after Focal Ablation (ie, PI-FAB) and Transatlantic Recommendations for Prostate Gland Evaluation with MRI after Focal Therapy (ie, TARGET), as well as pearls and pitfalls in the detection of tumor recurrence and medium- and long-term mpMRI surveillance of the post-focal therapy prostate, are also discussed. This review aims to provide a valuable reference for radiologists involved in the care of patients in the evolving field of prostate cancer focal therapy. Keywords: MR Imaging, Urinary, Prostate, Neoplasms-Primary, Focal Therapy, Prostate Cancer, MRI, Surveillance, Tumor Recurrence Published under a CC BY 4.0 license.

Keywords: Focal Therapy; MR Imaging; MRI; Neoplasms-Primary; Prostate; Prostate Cancer; Surveillance; Tumor Recurrence; Urinary.

Figure 1:

Images in a 67-year-old male patient with biopsy-proven Gleason grade 3 + 4 prostate cancer. Case illustrates pretreatment DCE upstaging tumor and altering clinical management. (A–D) Images from pretreatment MRI. (A) Axial T2-weighted image, (B) high-b-value DW image, and (C) ADC map demonstrate a T2-weighted hypointense lenticular subcapsular lesion in the right anterior transition zone midgland with restricted diffusion (arrow). Based on biparametric MRI findings, this lesion is smaller than 1.5 cm and would thus be graded PI-RADS 4. However, on (D) DCE images, the enhancing area is found to be larger than 1.5 cm and extending to the periurethral transition zone (arrow). Findings from targeted biopsy of the lenticular subcapsular lesion and systematic biopsy of the periurethral transition zone adjacent to the lesion were positive for Gleason grade 3 + 4 prostate cancer. This patient had originally been considered for focal cryoablation. However, given the periurethral location of the lesion, cryoablation would be ineffective, as the urethral warming catheter would prevent periurethral tissue from reaching the minimum lethal freezing temperature. Hence, IRE was employed instead. (E–I). MR images 1 year after IRE of the right periurethral transition zone. (E) Axial and (F) sagittal T2-weighted images show hypointense scarring with a cystic cavity at the treatment site (arrow), representing a urinoma, characteristic of post-IRE changes. (G) High-b-value DW image and (H) ADC map demonstrate signal void at the treatment site and no residual restricted diffusion is seen. (I) DCE image shows no focus of enhancement to suggest residual or recurrent tumor. Post-IRE MRI finding is PI-FAB 1/TARGET 1. Findings from 1-year post–focal therapy surveillance targeted biopsy at the treatment site were negative, with no residual cancer. ADC = apparent diffusion coefficient, Ax = axial, DCE = dynamic contrast-enhanced, DWI = diffusion-weighted imaging, IRE = irreversible electroporation, PI-FAB = Prostate Imaging after Focal Ablation, PI-RADS = Prostate Imaging Reporting and Data System, T2WI = T2-weighted imaging, TARGET = Transatlantic Recommendations for Prostate Gland Evaluation with Magnetic Resonance Imaging After Focal Therapy.

Figure 2:

Images in a 77-year-old male patient with prostate cancer. Case illustrates adequate treatment with expected post–focal therapy changes. (A–D) Images from pretreatment MRI. (A) Axial T2-weighted image, (B) high-b-value DW image with (C) corresponding ADC map, and (D) DCE image show focal T2-weighted hypointense lesion with restricted diffusion and early enhancement in the anterior transition zone to the right of the midline (arrow). The lesion was assigned PI-RADS category 5. Targeted biopsies showed Gleason gradeç 3 + 4 prostate cancer. Patient underwent focal cryoablation of bilateral anterior transition zones. (E–H) MR images 1 year after focal cryoablation. (E) Axial T2W image shows hypointense scarring with linear margins in bilateral anterior transition zones (arrowheads) with associated volume loss, capsular retraction, and adjacent periprostatic fibrosis. Previously seen PI-RADS 5 lesion is no longer visualized. (F) High-b-value DW image and (G) ADC map demonstrate signal void at the treatment site with no residual restricted diffusion. (H) DCE image shows no focus of enhancement to suggest residual or recurrent tumor. ADC = apparent diffusion coefficient, DCE = dynamic contrast-enhanced, DWI = diffusion-weighted imaging, PI-RADS = Prostate Imaging Reporting and Data System, T2WI = T2-weighted imaging.

Figure 3:

Images in a 76-year-old male patient with prostate cancer. Case illustrates treatment failure with in-field residual tumor. (A–D) Images from pretreatment MRI. (A) Axial T2-weighted image, (B) high-b-value DW image with (C) corresponding ADC map, and (D) DCE image show focal hypointense lesion with restricted diffusion and enhancement (arrow) in the right posterior peripheral zone. Lesion was assigned PI-RADS category 4. Targeted biopsies showed Gleason grade 3 + 4 prostate cancer. Patient underwent focal cryoablation of the right posterolateral peripheral zone. (E–H) MR images 1 year after focal cryoablation. (E) Axial T2-weighted image shows ill-defined intermediate to low signal intensity at the site of the tumor (arrowheads) with absence of volume reduction, raising concern for inadequate treatment. Furthermore, (F) axial high-b-value DW image, (G) ADC map, and (H) DCE image show that the lesion in the right posterior peripheral zone at the ablation zone has increased in size (arrow) with persistent restricted diffusion and enhancement. Post–focal therapy MRI finding is PI-FAB 3/TARGET 5. Histopathology revealed Gleason grade 3 + 4 in-field residual tumor. In this case, the initial tumor could have been preferentially treated with another modality such as high-intensity focused ultrasound, given its small size and posterior location near the neurovascular bundle. ADC = apparent diffusion coefficient, DCE = dynamic contrast-enhanced, DWI = diffusion-weighted imaging, PI-FAB = Prostate Imaging after Focal Ablation, PI-RADS = Prostate Imaging Reporting and Data System, T2WI = T2-weighted imaging, TARGET = Transatlantic Recommendations for Prostate Gland Evaluation with Magnetic Resonance Imaging After Focal Therapy.

Figure 4:

Images in a 75-year-old male patient with prostate cancer. Case illustrates in-field recurrence. (A–E) Images from pretreatment MRI. (A) Axial and (B) sagittal T2-weighted images, (C) high-b-value DW image, (D) ADC map, and (E) DCE image show a hypointense right transition zone periurethral tumor with restricted diffusion and enhancement (arrow). The lesion was assigned PI-RADS category 4. The patient underwent IRE of the right periurethral transition zone. (F–J) MR image 1 year after IRE. (F) Axial T2-weighted image shows hypointense scarring in the right anterior transition zone (arrowheads). However, a new lesion is seen at the margin of the treatment site (arrow) demonstrating (F) T2-weighted hypointense signal, (G) hyperintense signal on DW image, (H) hypointense signal on ADC map, and (I) focal enhancement on DCE image, suspicious for in-field recurrence. Post-IRE MRI finding is PI-FAB 3/TARGET 5. On (J) PSMA PET/CT image, the lesion corresponds with a PSMA-avid focus. Biopsy after IRE revealed Gleason grade 4 + 4 with tertiary Gleason pattern 5. The patient will be undergoing radical treatment. ADC = apparent diffusion coefficient, Ax = axial, DCE = dynamic contrast-enhanced, DWI = diffusion-weighted imaging, IRE = irreversible electroporation, PI-FAB = Prostate Imaging after Focal Ablation, PI-RADS = Prostate Imaging Reporting and Data System, PSMA = prostate-specific membrane antigen, Sag = sagittal, T2WI = T2-weighted imaging, TARGET = Transatlantic Recommendations for Prostate Gland Evaluation with Magnetic Resonance Imaging After Focal Therapy.

Figure 5:

Images in a 77-year-old male patient with prostate cancer. Case illustrates out-of-field tumor recurrence. (A–D) Images from pretreatment MRI. (A) Axial T2-weighted image, (B) high-b-value DW image, (C) ADC map, and (D) DCE image show a hypointense lesion in the right anterior peripheral zone midgland with restricted diffusion and enhancement (arrow). The lesion was assigned PI-RADS category 4. The patient underwent cryoablation of the anterior aspect of bilateral prostate lobes. (E–H) MR images 1 year after focal cryoablation. (E) Axial T2-weighted image demonstrates volume loss, capsular retraction, and hypointense scarring in bilateral anterior peripheral zones (arrowheads) in keeping with expected postablation changes. No focus of enhancement or restricted diffusion is seen in the postablation zone to suggest residual tumor. In the left posterior peripheral zone apex outside of the ablation zone, there is a new lesion (arrow) with (E) T2-weighted hypointense signal, (F) hyperintense signal on high-b-value DW image, and (G) hypointense signal on ADC map with (H) enhancement, suspicious for tumor recurrence. Post–focal therapy MRI findings are PI-RADS score 4. Histopathology revealed Gleason grade 3 + 4 out-of-field recurrence. ADC = apparent diffusion coefficient, DCE = dynamic contrast-enhanced, DWI = diffusion-weighted imaging, PI-RADS = Prostate Imaging Reporting and Data System, T2WI = T2-weighted imaging.

Figure 6:

Images in a 62-year-old male patient with prostate cancer. Case illustrates challenges of targeted biopsy after focal therapy with out-of-field recurrence despite prior negative biopsy findings. (A–D) Images from pretreatment MRI. (A) Axial T2-weighted image, (B) high-b-value DW image, (C) ADC map, and (D) DCE image show T2-weighted hypointense lesion in the subcapsular right anterior peripheral zone midgland with restricted diffusion and enhancement (arrow). Lesion was assigned PI-RADS category 4. Patient underwent focal cryoablation of the right anterolateral apex and midgland. (E–H) MR images 1 year after focal cryoablation. (E) Axial T2-weighted image shows hypointense scarring in the right anterior peripheral zone with volume loss and capsular retraction (arrowheads). No focus of restricted diffusion or enhancement is seen at the ablation zone to suggest residual tumor. However, there is interval development of a PI-RADS 3 lesion in the left anterior transition zone (arrow) with (E) T2-weighted hypointense signal, (F) moderately hyperintense signal on DW image, (G) hypointense signal on ADC map, and (H) enhancement. Findings from 1-year postablation surveillance targeted biopsy at the left anterior transition zone were negative. (I–L) MR images 3 years after focal cryoablation. (I) Axial T2-weighted image, (J) high-b-value DW image, (K) ADC map, and (L) DCE image show that the lesion in the left anterior transition zone (arrow) has increased in size with persistent restricted diffusion, now PI-RADS 4. Biopsy was performed and histopathology revealed Gleason grade 4 + 3 out-of-field recurrence. Earlier negative biopsy findings may have been due to sampling error because of postablation scarring and fibrosis. ADC = apparent diffusion coefficient, DCE = dynamic contrast-enhanced, DWI = diffusion-weighted imaging, PI-RADS = Prostate Imaging Reporting and Data System, T2WI = T2-weighted imaging.

Figure 7:

Images in a 62-year-old male patient with prostate cancer. Case illustrates in-field recurrence apparent at 5-year postcryoablation surveillance mpMRI despite prior negative findings at mpMRI and biopsy of the ablation site. (A–D) Images from pretreatment MRI. (A) Axial T2-weighted image, (B) high-b-value DW image, (C) ADC map, and (D) DCE image show hypointense lesions in the right and left anterior peripheral zone apex with restricted diffusion and enhancement (arrows). Lesions were assigned PI-RADS category 4. Patient underwent focal cryoablation of bilateral anterior apex and midgland. Findings from 1-year postablation MRI (not shown) were negative for residual or recurrent tumor. Systematic biopsy findings 1 year after focal therapy were also negative. (E–H) MR images 3 years after focal cryoablation. (E) Axial T2-weighted image shows hypointense scarring in bilateral anterior peripheral zone with volume loss and capsular retraction (arrowheads). No suspicious focus is seen on (F) high-b-value DW image, (G) ADC map, and (H) DCE image to suggest residual or recurrent tumor. (I–L) MR images 5 years after focal cryoablation. A lesion is now seen in the right anterior peripheral zone apex (arrow). (I) On T2-weighted image, the lesion is obscured by hypointense scarring, but it demonstrates (J) hyperintense signal on high-b-value DW image, (K) hypointense signal on ADC map, and (L) enhancement on DCE image. Post–focal therapy MRI finding is PI-FAB 3/TARGET 5. Histopathology revealed Gleason grade 3 + 4 in-field recurrence. ADC = apparent diffusion coefficient, DCE = dynamic contrast-enhanced, DWI = diffusion-weighted imaging, PI-FAB = Prostate Imaging after Focal Ablation, PI-RADS = Prostate Imaging Reporting and Data System, T2WI = T2-weighted imaging, TARGET = Transatlantic Recommendations for Prostate Gland Evaluation with Magnetic Resonance Imaging After Focal Therapy.