Prostate cancer and Brachytherapy
Prostate cancer is well suited to brachytherapy. The prostate gland is located under the bladder and in front of the rectum, and it is imperative that the radiation be focused in the prostate to avoid serious side effects. The prostate gland is also close enough to the skin that it can be easily accessed by brachytherapy needles.
There are two major methods of prostate brachytherapy, permanent seed implantation and high dose rate (HDR) temporary brachytherapy. Permanent seed implants involve injecting approximately 100 radioactive seeds into the prostate gland. They give off their radiation at a low dose rate over several weeks or months, and then the seeds remain in the prostate gland permanently.
HDR temporary brachytherapy instead involves placing very tiny plastic catheters into the prostate gland, and then giving a series of radiation treatments through these catheters. The catheters are then easily pulled out, and no radiactive material is left in the prostate gland. A computer-controlled machine pushes a single highly radioactive iridium seed into the catheters one by one. Because the computer can control how long this single seed remains in each of the catheters, we are able to control the radiation dose in different regions of the prostate. The tumor gets a higher dose, helping to ensure that the urine passage (urethra) and rectum will receive a lower dose. This ability to modify the dose after the needles are placed is one of the main advantages of temporary brachytherapy over permanent seed implants.
Andy Grove (chairman of Intel) chose the HDR procedure after analyzing all the available forms of treatment, including permanent seeds. He made the analogy that this treatment was like a “smart bomb”, whereas permanent seeding was a more crude “carpet bombing” treatment. He wrote about his experience in a Fortune magazine article in 1996.
What Does HDR Treatment Involve?
Treatment frequently consists of a combination of three separate therapies:
High-dose-rate temporary brachytherapy
Moderate dose external beam radiation
Short term hormonal therapy
This is a three-pronged attack against the cancer, also known as “triple modality therapy”. Sometimes the external radiation or hormone therapy is omit. You may wonder why you would even want to add external beam radiation. Cancer cells may migrate outside the prostate gland, known as “extra-prostatic extension”. Treatments like the radical prostatectomy and permanent seed implant alone may miss cancer cells which have escaped outside the prostate into the surrounding tissues. Another issue is that scans like the CT, MRI, ultrasound, and Prostascint are far from perfect in their ability to detect cancer cell spread outside the prostate. Even though these scans may not show cancer spread beyond the prostate capsule, it can still be present. The external beam radiation is used to target those areas surrounding the prostate gland. The probability that cancer has spread beyond the prostate gland can be estimated by the Partin tables.
The HDR procedure may differ at other hospitals. Some hospitals may insert 18- 25 catheters hollow plastic needles into the prostate gland. These are placed using anesthetic, and rectal ultrasound guidance. After the needles are placed, the doctor performs a CT scan and a computer plan which will calculate how long the radioactive source will stay in each needle. Three times over the following 24 hours, the needles are hooked up to the brachytherapy machine (HDR remote afterloader), and a treatment is given. During those 24 hours the patient will remain in a hospital bed.
The external beam component is given in a moderate dose, 4500 centigray divided over 4 – 5 weeks. This compares with the standard 7200 centigray divided over 8 weeks which would be required if you were having external beam radiation alone. FOr some patients, your doctor will suggest using intensity modulated radiation therapy and daily ultrasound verification that the prostate is centered in the radiation field (BAT). The reduced dose and precision targeting of IMRT may result in a lower risk of side effects. Some patients may receive broader radiation fields if there is a possibility that their lymph nodes contain cancer.
Mostly, patients suitable for HDR are offered a treatment using HDR alone without any external beam radiation for early prostate cancer. This is known as “HDR monotherapy”. If HDR is given without external beam, a higher dosage must be given, over 3 – 6 treatment fractions which may require two separate implants. There is not as much experience or results using HDR alone as there is with using HDR + external beam.
For some patients, doctors recommend short term hormonal ablationtherapy which is usually started 3 months before the brachytherapy, and continued for 3 – 12 months afterwards. The hormone therapy consists of a once-every-three-month injection of Lupron or Zoladex, and an antiandrogen medication like Casodex. The hormone therapy will shrink the cancer, shrink the prostate gland, reduce the PSA, and hopefully increase the cure rate from brachytherapy because there will be less cancer cells for the brachytherapy to kill. Studies have shown that adding hormonal therapy to radiation can increase the tumor control rates, notably for Gleason 7 and higher or PSA 10 or higher. Patients with a low-risk prostate cancer may be recommended to take a shorter duration of hormone therapy, or none at all. Patients with high-risk prostate cancer may be recommended to take triple hormone blockade for approximately 15 months.
Who can have this treatment?
HDR brachytherapy program can be used for a wide range of prostate stages, PSA values, and tumor grade. The components and dosages are modified for those with low, intermediate, or high risk prostate cancer. This treatment can also certainly be used for many tumors which are considered too advanced for radical prostatectomy. As long as there is no obvious spread to distant areas of the body like the bones this treatment can be considered. For early stages, HDR treatment is an alternative to the radical prostatectomy, but with less side effects. Eligible patients usually include:
Any tumor stage (T1 – T3)
Almost any size prostate gland (large glands will require hormone therapy prior to brachytherapy)
No known spread of cancer to other parts of the body, like the bones or lymph nodes
Previous trans-urethral resection of prostate (TURP / TUPR) is okay, but there may be a higher chance of urinary control problems.
Check with your doctor for your particular health care needs.