Contributed by Samuel Peretsman, MD
HIFU, or high intensity focused ultrasound, is a technique to generate heat in a very small area.
Now think about it, have you ever been harmed by sound?
Sound waves originate from a source. Typically, we encounter sound waves spreading out from a source and we only are bothered by amplitude of the sound (think sonic boom of a jet or a shrill fire alarm). However, sound can be collected from many adjacent sources at once, (like a transducer, for example) and all of the waves aimed at a single point.
These sound waves, concentrated in one spot, create tremendous vibration in the molecules they strike, thus generating heat. So all the good, as well as the side effects of HIFU, are created by this heat. As I say to many a HIFU candidates – this isn’t magic, just well-aimed heat!
Since we are killing the cancer by heating the tissue, the targeted tissue will swell. This swelling is totally normal, but can lead to compression on the urethra (as it passes through the prostate) until the swelling resolves. Hence, the patient awakens from HIFU therapy with a catheter draining the bladder. The catheter, either urethral or suprapubic, is removed once the swelling resolves. This may take a few days, or a few weeks, depending on the size of the gland that was treated.
So, in the ideal case, that’s it! A slightly weak urinary stream occurs from the swelling, but otherwise no pain and no adverse effects.
How can other side effects occur in some cases?
Based on the size and location of the cancer within the prostate, other structures may be very close, and will therefore be heated.
The urethra inside the prostate is a paper thin membrane and can slough off if exposed to too much heat (think of the superficial skin peeling off after a sunburn). Just like the top layer of skin regrows after a sunburn, the urethra regrows inside the ablated prostate. Urethral heating is less of an issue with focal HIFU or partial gland treatment because less of the urethra is typically affected by the heat. In the traditional, whole prostate treatments, this was more common. If the urethra and adjacent tissue slough, it can block urine flow. If this happens a patient may need to visit the urologist to have this tissue removed and clear the passageway for urine from the bladder. Over time, the urethra heals back over and the issue will be resolved.
Another potential side effect is a bladder neck contractures, or apical prostatic strictures, which may result in a weak urinary stream. These are now rare and are created by too much heat directed at these two ends of the prostate. They can be remedied by the urologist dilating or incising the scar tissue using an endoscope.
Erectile dysfunction, following HIFU, is a result of heating the adjacent penile blood vessels and nerves, particularly near the apex of the prostate as it forms the urethra in the penis. Overall, erectile dysfunction is 0-20% after HIFU, much lower than with other therapies.
This would be the result of intentionally aiming the heat near these nerves due to the fact that the cancer may lie against the prostate capsule right next to these nerves and blood vessels. To ensure the cancer is treated thoroughly, the area is heated but nearby structures may receive some of the heat and may stop functioning as well. The dysfunction is typically temporary and has no late worsening.
Primary incontinence, like that after radiation, has a near zero probability with HIFU. If the very apex of the prostate, which is right next to the urinary sphincter, is heated vigorously, then the control valve of the sphincter can scar and stiffen.
Lastly, since the prostate lies on the anterior wall of the rectum, you may have heard of the risk of heat damaging the rectum during HIFU. It is important to understand that there are numerous surgical precautions that HIFU doctors take, in order to avoid heating this rectal wall while treating the prostate. The Sonablate HIFU device itself, is engineered with multiple safety stops to minimize rectal wall heating. If, in spite of all these measures, the rectal wall integrity is compromised, a small connection, or a fistula, may form between the two structures. This is treated by leaving a urinary catheter in the bladder until the fistula heals and closes.
Overall the long term side effects of Sonablate HIFU for prostate cancer are minimal. This is what makes this therapy attractive to the many patients. Patient selection, thorough planning, and meticulous execution are what create the balance of good cancer control and maintaining a high quality of life.
About the Author
Dr. Samuel J. Peretsman has been a treating HIFU surgeon since February 2006. He has served on HIFU advisory boards, quality assurance committees, provided proctorships and invited HIFU lectures.
Peretsman completed his urologic oncology fellowship at Memorial Sloan-Kettering Cancer Center. He relocated to Charlotte in 1995 after 5 years serving as the urologic oncologist for the US Air Force Medical Corps. In Charlotte he has been instrumental in developing early programs for prostate cancer service lines including cryoablation, brachytherapy and robotic prostatectomy.
He was Charlotte’s first elected member to the Society of Urologic Oncology. His peers elect him to city (Charlotte), state (North Carolina,) and national lists of “Best Doctors.”