We sought to determine the role of MRI-guided biopsy to confirm visible tumours in the treatment planning process of focal radiotherapy boost for prostate cancer.
32 patients with localized prostate cancer and a visible dominant tumour nodule on MRI corresponding to histopathology on prior diagnostic TRUS-guided biopsy were prospectively enrolled between 2012 and 2015.
Patients underwent a confirmation MRI-guided tumour biopsy using an integrated diagnostic and interventional MRI technique in a 3T scanner (Verio, Siemens) using an endorectal coil system (Sentinelle, InVivo) and transperineal template under online stereotactic navigation (Aegis, Hologic).
Images were acquired with needles in situ to evaluate tumour-targeting accuracy.
Tumours were scored according to PIRADS v2 classification and PIRADS=3-5 lesions were targeted for biopsy.
Malignancy was confirmed in all (13/13) PIRADS=5 tumours, 32/35 PIRADS=4 tumours, and 1/4 PIRADS=3 tumours.
The three negative single core samplings of PIRADS=4 tumors are suspected to be marginal misses.
Few patients (n=3) were upgraded to high-risk Gleason 8 disease.
Biopsy confirmation of PIRADS= 4 and 5 lesions is not necessary in the treatment planning process for focal radiotherapy boost, but remains relevant for PIRADS=3 lesions.
Our observation of needle deflection by tumours highlights errors in limited sampling, and potential challenges if using alternate US/MRI fusion guidance strategies.
Strategies to mitigate this problem include multiple sampling of tumors, and imaging confirmation of successful central tumor targeting.
MRI-guided biopsy had limited impact on the treatment planning process for focal radiotherapy boost in prostate cancer.
Our clinical trial has been amended to omit mandatory MRI-guided biopsy prior to focal boost therapy