Most cancers of the prostate are what we call multifocal. This means that the cancer involves several areas of the prostate and therefore requires therapy that treats the whole prostate or what is called whole gland therapy.
Increasingly, there is evidence that there is a subgroup of patients who have prostate cancer where only a small area of the prostate is occupied by a significant cancer which does not require whole gland therapy but only the cancerous area to be treated and leave the rest of the prostate alone (similar to a lumpectomy in breast cancer).
Focal therapy involves the destruction of the small area of localised cancer and the preservation of the rest of the prostate. Focal therapy has become possible because of improved assessment of the prostate with imaging such as multiparametric MRI and thorough biopsy sampling often with transperineal template biopsy techniques.
The various forms of focal therapy include:
- Cryotherapy (freezing)
- High Intensity Focused Ultrasound (HIFU)
- TOOKAD (light stimulated destruction of tumour)
- Focal Brachytherapy using radioactive seeds
- Irreversible Electroporation (NanoKnife therapy)
All of these treatments aim to destroy the significant localised prostate cancer and a margin of tissue around it, sometimes incorporating half of the prostate but preserving the rest of the prostate. Each of these energy sources have their benefits and disadvantages.
What is focal NanoKnife (IRE) ablation?
NanoKnife (or irreversible electroporation – IRE) focal ablation is the use of high-powered pulsed electricity to destroy the small section of the prostate involved with the cancer. As with all other forms of focal therapy, it aims to preserve the remainder of the prostate, decreasing treatment side-effects such as impotence and incontinence. As it does not rely on heat or freezing, it has the unique potential to preserve adjacent structures, thus improving the likelihood of preservation of continence and potency.
The NanoKnife uses an electrical field that can be precisely targeted to create tiny holes in tumour cells while not affecting adjacent organs. Ultra-precision allows treatment of particular areas within the prostate that are difficult to reach by other minimally invasive techniques. Better treatment appears to be produced in small tumours.
What are the risks and benefits of focal NanoKnife therapy?
As with all focal therapies, there are less side effects compared to radical prostatectomy surgery and radiotherapy. In particular, there is a much lower chance of incontinence, impotence, bowel damage and other complications often associated with surgery or radiotherapy. The treatment is much simpler to perform and is generally performed as a day only or short stay procedure.
The particular advantage of NanoKnife therapy over other energy sources appears to be its non-reliance on thermal energy, therefore its relative preservation of adjacent structures such as the erection nerves and the urethra and can be repeated if required, as well as being able to be used after previous radiotherapy.
The disadvantages of all focal therapy programs including NanoKnife therapy is that there is no long-term data on cancer outcomes and it requires much closer follow-up. Guidelines are still being currently developed to select the correct patients for focal therapy treatments, and as such, there is always a risk that the cancer will reappear in another part of the prostate. Also, there is a theoretical concern that if subsequent surgery is required, the previous focal therapy may make that surgery more difficult. To date this has not been borne out in the small numbers of cases reported.
The procedure
The procedure is done under a general anaesthetic and takes approximately 45 minutes to perform. Four to six electrodes are placed through the skin behind the scrotum (the perineum) into the prostate under ultrasound guidance.
A pulsed high energy electricity current is then passed sequentially between each of the electrodes enabling the area of the prostate mapped out to be destroyed. The extent of the treatment depends on the results of the MRI and biopsies but will always incorporate a 1cm safety margin around the cancer. The electrodes are also placed to avoid damage to adjacent structures.
Professor Mark Frydenberg performs NanoKnife focal therapy at Cabrini Hospital.