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MRI-guided biopsy of visible tumors to guide focal therapy

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Objectives:

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.

Methods:

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.

Results:

•52 tumours were targeted for biopsy.
•8 of 35 PIRADS=4 lesions were negative on targeted biopsy, 5 of which were confirmed false negative with additional sampling, and the remaining three were suspected of marginal miss.
•All false negative samples occurred with dense tumours ≤1.2cm whereby needles were all deflected at the margin of the tumour. 
•The majority of needles (70%) were deflected at the margin of tumours.
•The negative biopsy rate fell from 40% for single sampling to 13% for those with multiple sampling.
•Cores visualised at the centre of a tumour yielded a negative rate of 11%, while cores visualised at the deflected margin of the tumour yielded a negative rate of 42%. 
 
Discussion:

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.

Conclusions: 

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

 

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