Contributed by Samuel Peretsman, MD –
Prostate cancer can be treated in different ways including surgical removal (radical prostatectomy) or ablation. Ablation means destroying the prostate inside the body using a source of energy. The cancerous tissue and the normal tissue both get affected. The surrounding tissue and organs can also be affected by ablations, thus creating side effects.
What is ablation?
Ablations can be conducted with thermal sources or using radiation sources. Thermal sources are those that use extreme hot or cold temperatures to destroy tissue. Radiation sources can be beams from outside the body including, photon or IMRT (intensity –modulated radiation therapy), proton, neutron or radiation sources known as seeds, implanted in the body, which is called brachytherapy.
How does radiation work?
Radiation, by definition, is an energy source that must pass through the normal body organs to reach the target cancer/organ such as the prostate. In some cases, radiation will be surgically implanted in an organ and, in that situation, the radiation travels outward. It kills the cancer by damaging the tissue’s genetic material. The cancer cell death, normal organ death, and adjacent organ damage is not immediate but may take place over several weeks or months. After the tissue’s genetic material is altered, the cells die off over time.
The body responds to the tissue damage with scar tissue and growth of new thin walled blood vessels. Tissue that is damaged, but does not die, can rarely be genetically altered and create a new cancer in the target organ or an adjacent organ that had been irradiated. Additionally, radiation energy particles travel in waves and these waves do not stop abruptly. Hence the technique cannot easily be targeted to only treat part of the prostate as it’s difficult to create sharp treatment boundaries. In other words, areas and organs outside the prostate may be affected and damaged after undergoing radiation therapy for prostate cancer. For some men this leads to unwanted side effects such as difficulties with urinary function and erectile dysfunction. Advances in radiation techniques have diminished skin, hair, bowel toxicities. Mostly the side effects during therapy can be bladder or bowel irritation and urgency, weak urinary stream, and fatigue. These processes are what distinguish radiation therapies from thermal therapies.
How is HIFU different from radiation?
HIFU, or high intensity focused ultrasound, is essentially a heat source. All living tissue is composed of cells that are built from proteins. When affected by elevated temperatures, the proteins are degraded and the cells die. This occurs to all cells, cancerous or normal. Heat can be delivered by focusing sound waves from a distance (think a magnifying glass generates extreme heat by focusing light on a leaf and setting it ablaze).
Unlike radiation, the low energy sound waves of HIFU do not damage the tissue they pass through. The sound waves are concentrated at a precise focal point creating high temperatures in that small area. Consequently, the immediate bother and harm are less, and the delayed damage and problems (such a recurrent bleeding or second cancers) are avoided. With HIFU there is swelling of the tissue and potentially a weak stream until the swelling resolves over days to a couple weeks.
The treated, or targeted, tissue with HIFU dies immediately. The body absorbs it and replaces the area with benign scar tissue. Since the prostate connects to the urethra, occasionally some tissue passes through that route (not if the area near the urethra is avoided however). This healing is the body’s normal response to tissue death (think of burning your finger on the stove). There are no delayed or late manifestations.
What happens to your body after radiation?
Following prostate or pelvic radiation the prostate and the adjacent organs recover from the initial irritation and swelling. The genetic material of all these tissues has been damaged and so the cells die off slowly as they try to grow. The cancerous cells grow faster and so they are more vulnerable to this effect. The adjacent rectum, bladder, urethra, nerves and blood vessels that are harmed but do not die, then recover and heal. Having been damaged by the radiation, these tissues do not heal normally and they lead to thin-walled blood vessels, development of delayed but potentially progressive scarring (diminishing erections or narrowing the urine channel), and rarely, forming a new second cancer.
In conclusion, these are fundamental differences between radiation ablation and HIFU ablation. Later we’ll discuss differences between heat and cold ablation, and ablations and surgical removal.
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, and provided proctorships and invited HIFU lectures.
Peretsman completed his urologic oncology fellowship at Memorial Sloan-Kettering Cancer Center. He located 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.”