SpaceOAR

By Dr. Jared Heiner
Special to The Idaho Statesman
February 19, 2018

SPACEOAR AND PROSTATE CANCER PROGRESS

Prostate cancer continues as one of the leading causes of cancer death among American men. Lung cancer causes the most cancer death for American men. Prostate cancer and colon cancer vie for the number two spot. Prostate cancer occurs more commonly later in life and as the average lifespan continues to increase it should become an increasingly common challenge for the medical field to combat. About 1 in every 41 American men will die of prostate cancer with around 30,000 men succumbing to it each year in our country.

However, prostate cancer is very treatable and is usually very slow growing. Indeed, many men are diagnosed with slow-growing prostate cancer that doesn’t require any treatment at all. Over 2.9 million American men are still alive today after having been diagnosed with prostate cancer at some point in their lives. Many of them underwent prostate cancer treatment and others pursue a management strategy of observation and surveillance to make sure it doesn’t become more aggressive.

Physicians, scientists, epidemiologists, and politicians have contributed to a decade of controversy about whether or not we should screen for, diagnose, or even treat prostate cancer. The fact that all men will develop prostate cancer eventually if they live long enough has led to over-diagnosis and over-treatment. Many men have been treated for a slow-growing prostate cancer that perhaps never would have caused them any symptoms or threatened their health. The challenge has been determining who needs diagnosis and treatment and who doesn’t. In my opinion, if a man still enjoys a 10 year life expectancy it is worth knowing his PSA level and administering a digital rectal exam (the measures we use to screen for prostate cancer.) We then judiciously determine with the patient what to do with that information.

The prostate is a golf ball-sized gland that sits below the bladder and is shaped like a donut. Its purpose is to make semen. The urine has to pass through the middle of the prostate to get out. As a man ages his prostate continues to grow and get bigger and the donut hole through which the urine passes gets tighter. That makes it more difficult for men to urinate. Prostate cancer is another problem that occurs in the gland and it is more common as men age. The prostate has its own particular anatomy and prostate cancer tends to arise in the edges or periphery of the gland while the central portion grows and causes trouble urinating. If we think of the prostate as an orange cancer tends to arise in the peel while the juicy, pulpy part tends to cause the trouble urinating.

Radiation therapy remains a mainstay of prostate cancer treatment. In general, cancer propagates by unchecked division of cancer cells. When cancer cells divide, their numbers multiply. (I’m actually not trying to interject any type of mathematical philosophy or confusion here.) When one cell divides into two the number of cells has doubled; multiplied. Colonies of cancer cells divide repeatedly until they take over the tissues and organs into which they spread. The process of cell division requires a cell to make a copy of itself by using a protein template called DNA. DNA acts as a blueprint or masterplan and it allows a cell to multiply in numbers and maintain its cancerous properties in the new cells. Radiation damages the cancer cell DNA making it difficult for cells to make functional self-copies.

Radiation can be delivered to the prostate in several forms. External beam radiation involves shooting x-rays through the skin into the prostate. Typically, the radiation will be given every day, Monday through Friday for eight or nine weeks. The patient comes in for a short visit and lies down on a treatment table. A computer locates the prostate and delivers a dose of radiation focused on the prostate according to the plan devised by the radiation oncologist. No treatment is done on the weekends.

Brachytherapy or “radioactive seed” implantation involves small radioactive pieces of metal that are shaped like tiny pieces of rice. With the patient anesthetized small needles are inserted through the skin between the scrotum and the anus into the prostate gland under ultrasound guidance and anywhere from 50 to 100 seeds are implanted into the prostate. Over the next 60 to 90 days the seeds give off their radiation directly into the prostate and then “burn out,” are no longer radioactive, and remain in the prostate. Another form of brachytherapy involves inserting small metal rods that remain in the prostate for a couple of days while radiation is delivered into the prostate on an inpatient basis.

While modern radiation therapy has improved the ability to focus the treatment where it is needed there is still some collateral damage to adjacent normal tissues such as the bladder and rectum. Those normal tissues also absorb some radiation. This can cause inflammation in the rectum, blood in the stool, painful bowel movements, diarrhea, pain while sitting, and rectal pressure and sometimes requires the patient to pause the therapy until the side effects improve. Rarely prostate radiation can lead to rectal cancer.

Men know all too well that the prostate sits right in front of the rectum. The notorious digital rectal exam, also known as a prostate check, finger wave exam, or other creative appellations is performed by placing a finger in the rectum. The clinician can feel the back surface of the prostate to check if there is any suspicious nodule or lump. There is only a small layer of fat measuring 2 or 3 mm separating the rectum and prostate. That means that radiation aimed at the prostate will also affect the rectum.

Enter the rectal spacer concept which pushes the rectum and prostate away from each other. Indeed, the above long-winded preamble was to set the stage for describing the FDA approved rectal spacer branded SpaceOAR. It is injected as a liquid into the space between the rectum and prostate and within 10 seconds turns into a soft gel that maintains 10 to 12mm of space between the rectum and prostate until the body reabsorbs it during the subsequent 6 months. This dramatically decreases the amount of radiation absorbed by the rectum by about 70%. A randomized study showed late rectal side effects occurred in 7% of radiation patients who had standard therapy and only 2% of patients who had the rectal spacer gel placed. The control group patients had worse side effects than the spacer patients who had fewer and milder side effects.

The rectal spacer definitely protects the patient from side effects of radiation. It remains to be seen whether SpaceOAR will allow us to change and improve cancer treatment with techniques such as dose escalation. For instance, perhaps with a bigger space between the rectum and prostate we can give higher doses of radiation over shorter periods of time. Maybe we can give the same total amount of radiation over the course of one month of treatments instead of two. Maybe these higher individual doses of radiation will better eradicate the cancer. We know that the rectal spacer decreases side effects. But could it help us improve our treatment of the cancer as well?

What are the down sides? With any invasive procedure there is always a risk of getting an infection or having bleeding. Perhaps the rectal wall could suffer some ulceration or reaction to the gel. Of 149 patients treated with the spacer in the prospective randomized study one patient had blood in the semen, another had blood in the urine, while yet another felt pressure down in the rectum. One patient reported pain in his thigh and another reported pain while sitting. None of these side effects required medication. No adverse events or allergic reaction related to the gel itself occurred. It may be that rectal spacer placement soon becomes the standard of care for patients undergoing brachytherapy or external beam radiation for prostate cancer.

For more information: https://www.spaceoar.com/patients/