Image-Guided IRE for Prostate Cancer: Why Electrode Placement Matters

Irreversible electroporation (IRE) is a focal prostate cancer treatment that uses short, high-voltage electrical pulses to disrupt cell membranes and cause cell death without relying primarily on thermal energy. Its primarily nonthermal mechanism may help limit injury to connective tissue and blood vessels, but the energy source alone does not make the procedure precise.

The treatment field is created between needle electrodes inserted around the tumour. Their position determines which tissue receives a sufficient electrical field and which tissue remains outside it. Accurate imaging therefore does more than guide the needles into the prostate gland. It defines the target, shapes the treatment plan and helps the operator balance cancer coverage against preservation of surrounding tissue.

MRI Defines the Treatment Target

In patients with clinically localized prostate cancer, multiparametric magnetic resonance imaging (mpMRI) helps define the tumour and its relationship to surrounding anatomy. It can show whether a lesion lies within the peripheral or transition zone, how far it extends through the gland and whether it approaches structures involved in urinary and sexual function.

This information is particularly important during focal treatment. Unlike radical prostatectomy or whole-gland radiation therapy, focal IRE aims to treat a defined area while preserving suitable surrounding prostate tissue. The operator must therefore understand the tumour’s relationship to the capsule, urethra, urinary sphincter and neurovascular bundles.

MRI findings should also be correlated with prostate biopsy results. A visible lesion may not represent all clinically significant disease within the prostate, while systematic or template biopsy may identify cancer beyond the apparent MRI target.

The planned treatment area should therefore reflect the combined distribution of imaging and histological findings rather than the visible lesion alone.

Electrode Placement Creates the Treatment Field

During IRE treatment, electrodes are introduced transperineally under real-time ultrasound guidance. Electrical pulses are delivered between selected electrode pairs, producing overlapping treatment zones around the cancer.

Several variables influence the resulting electrical field:

The number and spacing of the electrodes
The exposed length of each active tip
The insertion depth and angle
The pulse sequence delivered between electrode pairs

Small changes in these variables can alter the size and shape of the treated area.

An electrode that appears correctly positioned in a transverse ultrasound view may still be too shallow or too deep to cover the lesion along its full craniocaudal extent. Electrode position should therefore be assessed in more than one imaging plane before treatment begins.

The ablation zone is also not limited to the area visibly enclosed by the electrode shafts. It results from the interaction of the electrical fields generated between different electrode pairs. Treatment planning must account for how these fields overlap throughout the target volume.

Why Standardized Placement May Be Insufficient

Prostate tumours do not have a uniform shape. A small rounded lesion presents a different planning challenge from an elongated tumour extending toward the apex or capsule.

Lesions near critical structures can be particularly difficult to treat. An apical tumour may approach the external urinary sphincter, while a posterolateral lesion may lie close to a neurovascular bundle. Tumours near the urethra, bladder neck or rectum create different anatomical constraints.

A fixed grid can help maintain consistent electrode spacing, but predefined entry points may not reproduce every tumour’s three-dimensional shape. Individually selecting electrode angles and depths provides greater flexibility when the treatment field must be adapted to irregular anatomy.

Some specialist centres therefore place electrodes individually under continuous ultrasound guidance rather than relying exclusively on predetermined grid positions. This allows the configuration to be adjusted according to the tumour’s location, shape and relationship to nearby structures.

The purpose of individualized electrode placement during prostate IRE is to translate the MRI- and biopsy-defined target into a corresponding treatment configuration inside the gland.

The significance of this technique is not simply the method used to insert the needles. It is the operator’s ability to reproduce a three-dimensional treatment plan within the patient’s actual anatomy.

Real-Time Ultrasound During Treatment

MRI provides detailed information before treatment, but ultrasound offers the real-time feedback needed during electrode insertion.

The operator can use biplane ultrasound to monitor the position and depth of each electrode while viewing the prostate from different directions. This makes it possible to identify variations in electrode angulation and confirm that the active portions of the needles extend across the intended target.

Real-time imaging is also valuable because the prostate may deform or shift during the procedure. Pressure from the ultrasound probe, patient positioning and the insertion of multiple electrodes can affect the relationship between the planned target and the anatomy seen during treatment.

Continuous ultrasound guidance allows the operator to respond to these changes rather than assuming that the pretreatment plan remains perfectly aligned throughout the procedure.

The Limitations of Image Guidance

Image guidance improves treatment planning, but it does not eliminate uncertainty.

MRI can underestimate the true histological volume of a tumour, and biopsy can miss clinically significant disease. Registration between MRI and ultrasound may also be affected by deformation of the prostate.

The operator must account for this uncertainty when choosing the treatment margin. A larger field may improve the likelihood of covering microscopic extension but will treat more uninvolved tissue. A smaller field may preserve additional tissue while increasing the risk of leaving cancer near the edge of the target.

The appropriate balance depends on the reliability of the imaging, the distribution of the biopsy findings and the anatomical position of the tumour.

Even advanced imaging and accurate electrode placement cannot compensate for incomplete disease assessment or unsuitable patient selection. Whole-gland evaluation remains important because prostate cancer is frequently multifocal, and clinically significant disease may exist outside the MRI-visible index lesion.

Imaging After IRE

MRI remains useful after treatment. It can document the location of the ablation zone, establish a new anatomical baseline and identify findings that require further investigation.

Posttreatment imaging can be difficult to interpret, particularly during early healing. Edema, haemorrhage, inflammation and peripheral enhancement may occur after ablation. Over time, the treated area may contract and develop fibrosis or reduced signal intensity.

Focal nodular enhancement, persistent restricted diffusion or an enlarging soft-tissue focus may raise concern for residual or recurrent disease. However, a normal or non-suspicious MRI cannot reliably exclude persistent cancer.

Follow-up should therefore combine imaging with PSA monitoring and biopsy when clinically appropriate. The untreated portion of the prostate must also remain under surveillance because focal therapy treats a defined target rather than the entire gland.

Precision Depends on the Entire Workflow

IRE is often discussed in terms of its electrical pulses and primarily nonthermal mechanism. In practice, its precision depends on the imaging and procedural workflow surrounding the device.

The tumour must first be localized and mapped. Imaging findings must then be reconciled with biopsy results. Finally, the electrodes must be positioned so that the resulting electrical field covers the target without unnecessarily extending into surrounding tissue.

For patients and referring clinicians evaluating an IRE programme, the quality of this imaging-led planning may be as important as the treatment platform itself.