HDR Brachytherapy for Prostate Cancer
Prostate cancer is the model cancer for brachytherapy. The prostate gland is located under the bladder and in front of the rectum. It is vital that radiation therapy be focused in the prostate to avoid significant side effects. The prostate gland is also close enough to the skin that it can be easily reached 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 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 radioactive 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, the radiation oncologist is able to control the radiation dose in different regions of the prostate. The tumor can receive a higher dose, while the urine passage (urethra) and rectum 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.
What Does HDR Treatment for Prostate Cancer Involve?
This treatment frequently consists of a combination of three separate therapies:
- High-dose-rate temporary brachytherapy
- Moderate doses of Tomotherapy
- Short-term hormonal therapy (optional)
This is a three-pronged attack against the cancer, also known as "triple therapy." Sometimes the doctor can omit the Tomotherapy (external beam radiation) or hormone therapy.
However, external beam radiation is often included because cancer cells may migrate outside the prostate gland, known as "extra-prostatic extension.” Treatments like a radical prostatectomy and permanent seed implant alone may miss cancer cells which have escaped outside the prostate into the surrounding tissues.
Scans like CT, MRI, ultrasound, and Prostascint may not detect cancer cells that have spread outside the prostate. Even though these scans may not show cancer spread beyond the prostate capsule, it can still be present. External beam radiation helps 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
The HDR procedure can differ among hospitals. The radiation oncologist 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, a CT scan and a computer plan 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 weeks. This compares with the standard 8100 centigray divided over 9 weeks which would often be prescribed if the patient was having external beam radiation alone.
Many times, the radiation oncologist uses intensity modulated radiation therapy (IMRT) which does its own verification that the prostate is centered in the radiation field. 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.
HDR may also be used 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 monotherapy as there is with using HDR plus external beam, so the combination treatment may be a more proven choice.
The radiation oncologist may also recommend short-term hormonal ablation therapy, which begins three months before the brachytherapy and continues 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 there will be less cancer cells for the brachytherapy to destroy.
Studies have shown that adding hormonal therapy to radiation can increase the tumor control rates, notably for Gleason 7 and higher tumors or PSA 10 or higher. Patients with an early 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 (Lupron + Casodex + Proscar) for approximately 15 months.
Who Can Have This Treatment?
HDR brachytherapy can be used for a wide range of prostate stages, PSA values, and tumor grades. The components and dosages are modified for those with low, intermediate, or high risk prostate cancer. This treatment can also 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 may be considered. For early stages, treatment may be an alternative to the radical prostatectomy, but with less side effects.