HDR Monotherapy

Since its inception, HDR prostate brachytherapy has usually been given along with external beam irradiation. Although a very successful treatment, many patients found the external beam irradiation treatments inconvenient, and wished that they could have the HDR brachytherapy alone, without having to undergo the follow-up external beam. This is called HDR monotherapy.

By increasing the HDR dosage we can choose to omit the external radiation.

1. There are very few published results
2. It should not be used on everyone - possibly only for men with early stage prostate cancer
3. The best dosage and number of treatment fractions to use has not yet been determined.
4. To increase the HDR dose, often more fractions and/or two implants are required

Who can have monotherapy?

Monotherapy is an option for early stage prostate cancer, or more specifically "low risk" prostate cancer. These are the same patients who can have a permanent seed implant alone as treatment. Intermediate or high risk prostate cancer is better treated with a more comprehensive treatment strategy, such as external beam irradiation + HDR brachytherapy boost + temporary hormone therapy. This is how prostate cancer patients are commonly categorized into low, intermediate, and high risk categories:

Low Risk Prostate Cancer

• PSA less than 10
• Gleason score less than or equal to 6 (3 + 3)
• Tumor stage T1c or T2a: tumor on one side of gland, either a nodule is not felt (stage T1c) or else the nodule occupies less than half of the lobe (T2a).
• Ideally, biopsy shows:
• cancer on one side of the prostate gland only
• no perineural invasion
• no core sample shows over 25% cancer

In addition, it is best that the pathology report show that there is cancer on only one side of the prostate and that there is no "perineural invasion". It is preferable that there has not been a prior trans-urethral resection of prostate tissue (TURP).

What does the treatment involve?

The implant procedure is identical to the way we do HDR implants that are being combined with external beam irradiation. Plastic needles are placed through the skin into the prostate gland under anesthetic and rectal ultrasound guidance. A CT scan is then done for the computer planning of the dose that will be given to each of the needles. The dose will be higher than what we use when we are combining HDR with external beam.

Different hospitals are using different schedules and dosages for monotherapy. At CTCA we frequently use a single implant with three fractions of 1050 cGy each given over a 24 hour stay. Here is a table of some comparative dosages:

Although 1050 * 3 fractions = 3150 cGy may seem like a low dose, it is theoretically equal to a much higher dose than this because large fraction sizes are exponentially more powerful. It may be equal to approximately 9000 cGy of standard external beam irradiation. (Based on alpha-beta ratio of 3.0, and average tumor dose of at least 101% of prescribed dose.) Normal external beam irradiation usually gives between 6600 cGy and 7800 cGy to the prostate gland.

Comparison of HDR monotherapy versus permanent seeds alone

Benefits of permanent seeds alone

• Proven track record with 15 year results.
• Single day treatment. HDR requires an overnight stay in hospital and may require two implant procedures.
• Available in hundreds of cancer centers. HDR monotherapy is available in a handful of centers currently. HDR also requires more expensive equipment and more technical support.

Benefits of HDR monotherapy

• HDR is the most precise way to give radiation to the prostate, more accurate than seeds, protons, or IMRT. We can literally "sculpt the dose" in the prostate gland to give a higher dose to the peripheral zone and tumor and a lower dose to the urethra (urine passage) bladder and rectum.
• HDR avoids hot spots and cold spots. The amount of radiation given to each catheter is calculated after the implant is performed. This allows the computer to compensate for catheters which are too close or too far apart or too close to the urethra or rectum. With permanent seeds, if some of the 100 seeds are not injected into perfect position there is no way to compensate, and radiation hot and cold spots will occur. This can result in increased side effects, or a reduced chance of cure.
• HDR can provide better coverage to the tissues just outside the prostate gland (extracapsular) and the seminal vesicles. If there is early cancer spread into these areas that scans or a rectal exam did not detect, the HDR should be able to treat these areas anyway.
• Recent studies suggest that large treatment fraction sizes may have a very powerful effect against the cancer cells, versus the slow trickle release of radiation from permanent seeds.
• With HDR you do not need to wait for the radioactive seeds to be ordered and you do not need to pay thousands of dollars for the seeds.
• With HDR, there are no radioactive seeds left in the body after the procedure is over. You are not radioactive, and there are no restrictions on how close family members can come to you.
• Permanent seeds can migrate into the blood stream and end up in the lungs, or can be urinated out.

Conclusions

HDR Monotherapy is available as a treatment option for men with early (low risk) prostate cancer. However, monotherapy is relatively new and the combination of HDR plus external beam has a proven track record with very high success rates and relatively low side effect rates. For monotherapy the optimum dose, number of implants, and number of treatment fractions per implant is not known at this time.