SBRT

What is SBRT

SBRT stands for Stereotactic Body Radiation Therapy. It is also known as SABR (stereotactic ablative radiation therapy). It is a highly advanced form of targeted external beam radiation.  It is different from conventional radiation like IMRT in the following ways:

  1. The radiation is aimed more precisely. Typically gold markers are placed in the prostate to help with aiming, and the physician checks that the treatment is precisely aimed each day.
  2. A small area is treated, just the prostate with a few millimeters (1/4 inch) of additional tissue surrounding the prostate.
  3. A higher radiation dose is used each treatment, thus fewer treatments are required.
  4.  This treatment tends to be ablative – ie killing all or most cells within the target zone.

Because this treatment is so precise, a higher radiation dose can be given each day and fewer treatments are required.  Only 5 SBRT treatments are required instead of the 28 – 45 treatments typically recommended on a conventional radiation machine!

Results

SBRT is a newer technology, so there are fewer long term results then there are for surgery.  But we finally have 10 year results from Dr. Katz, and they are excellent!  These are the highlights from 236 men with a PSA less than 10, and a Gleason score of 3 + 3:

  • PSA was low and in control in 93% at the 10-year mark.
  • Cancer control in the prostate gland was 98.4%.   I.e. the cancer came back in the prostate gland in less than 2% of patients.
  • Only 3% had severe long term urinary symptoms, and 0% had serious long term rectal symptoms.   The average rectal and urinary symptom score was almost the same at 10 years as it was prior to treatment.

Why you should consider SBRT over other treatment options

There are many treatment options for prostate cancer. In expert hands, they all tend to have a good cure rate. It is important to research your options, see what treatments you are eligible for, and see what makes sense to you. I like SBRT because it is a relatively short treatment with little recovery time, an excellent cure rate, and typically mild side effects.

If you visit with many different doctors you may discover that they all recommend a different treatment.  Surgeons will recommend surgery, and radiation oncologists will recommend radiation.  There are many approved treatment options for prostate cancer, and there is not simply one was to treat it.

Who can have SBRT

Men with low-risk or favorable intermediate-risk prostate cancer can be treated with SBRT alone.

For men with high-risk prostate cancer (Gleason 8 – 10, and/or PSA over 20), it is not known if treating with SBRT alone is enough treatment. These men should probably have a combination of different treatments. One option for this is hormonal therapy for 12 – 36 months, SBRT boost for 2 – 3 treatments, and conventional radiation (IMRT) to the prostate and pelvic lymph nodes for 25 treatments.

Other limitations for SBRT are that the prostate gland should be small enough for SBRT, ideally less than 60cc (2 ounces), but occasionally up to 100cc. A normal prostate gland is about 30cc (1 ounce). There should not have been previous surgery on the prostate gland, i.e no prior TURP. It is preferable that there are no serious urinary symptoms before treatment starts. Patients also need to be able to tolerate having gold seeds inserted into prostate gland.

Treatment Steps and Schedule

There are multiple steps to preparing for and performing the SBRT treatment. Typically, during the first week we place the gold markers seeds and SpaceOAR hydrogel. During the second week we do the mapping and computer planning. During weeks 3 and 4 we do the actual SBRT treatments, which occur every second weekday.  The fastest all of this can be scheduled is a 15 day period, from the day you have the marker seeds placed, until the day of the final treatment.

The first step of course is to do a consultation, then complete any scans or staging tests that are required. Once we decide on SBRT as a treatment we need to get approval from your insurance company.

Next we place the 3 – 4 gold marker seeds into the prostate gland under ultrasound guidance, while you are under sedation. These seeds are not radioactive. They stay in the prostate gland permanently.   They are used to help the SBRT machine lock onto the prostate gland during treatment.  We do not try to place the marker seeds where the cancer is, they simply are placed inside the prostate gland. We will also usually do a SpaceOAR procedure at the same time, where a gel is injected in between the prostate and the rectum and it pushes these two organs apart. This will result in less radiation dose reaching the rectum. The gel is broken down by the body after 3 months.

We let the marker seeds and gel settle for a few days, then we do a CT-simulation, which is simply a CT scan of your pelvis, with you laying in the same position you will be in for each treatment. We also usually do an MRI scan of the pelvis on the same day.  The MRI can often show us the location of the cancer in the prostate gland.

The next step is called treatment planning, and this does not require your participation. The physician outlines everything he wants treated, and he prescribes a radiation dose.  The whole prostate is treated.  Extra radiation is often aimed at the tumor, and less radiation is aimed at the urethra (urine passage).    A dosimetrist creates a computer plan, which determines how many beams will be aimed at the prostate gland, from which angles, and how strong each beam is. The PhD physicist then does a dummy treatment run to make sure the plan will deliver the intended dose to the intended area.

Finally we have the actual treatments! There are 5 treatments, given approximately every second day. Each treatment takes about an hour. It is totally painless, like getting an X-ray done. You are free to do whatever you want the rest of the day. After the final treatment you can immediately return back to your usual life.

Side Effects

There are often no side effects during the 2 week treatment period. Then, over the following 6 weeks, the urine stream will typically slow down, you may have to urinate more frequently, and there can be some burning with urination. We prescribe Flomax to help with these symptoms. The bowel movements may be more frequent, or contain a little mucous or blood. These symptoms will typically all clear up, and many or most men report no residual side effects when I see them 3 – 6 months after the treatment.

In the long term, 6 months and beyond, the radiation can cause some permanent scarring or fibrosis in the prostate gland area. This can weaken the erections and can cause erectile dysfunction (ED) in some men. The urine passage (urethra) may become narrowed, slowing down the urine stream.  Occasionally a TURP or stretching of the urethra may need to be performed in the future.  The prostate will become shrunken and does not function normally after radiation.  It normally creates some fluid in the ejaculation, so the ejaculations will become dry but the sensation may still be the same.

Follow-ups

There is no test to prove that the cancer is cured. We monitor the PSA afterwards. We check the PSA 3 months after treatment, then every 6 months after that. As long as the PSA drops down to low levels and stays there, everything is good. PSA will typically drop to less than 1.0 by one or two years after the treatment, and down to 0.1 or 0.2 by the 5-year point.

Sometimes the PSA can bounce up and down a little, so if it rises during the follow-up period we calmly check it again 3 months later. If it continues to rise, and especially if it has risen at least 2.0 points above a previous minimum level, then we get concerned there can be a cancer recurrence. We will then order CT scans and a bone scan. We may also do a prostate biopsy.

Recurrences

If the cancer comes back in the bones or lymph nodes then the cancer is not curable and the usual treatment is to go on hormonal therapy, i.e Lupron.  Please note that after any type of prostate cancer treatment the cancer can come back in the bones or lymph glands – this is not something that is unique about SBRT!

If the cancer comes back only in the prostate gland, then we may refer you for Cryotherapy (freezing the prostate). SBRT has a very high rate of cancer control within the prostate. We see very few patients whose cancer comes back in the prostate.  The 10-year results show that cancer was found to come back in the prostate gland in only 1% of stage 1 patients.

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