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HYPO-FRACTIONATED RADIATION DOSAGE

and

CYBERKNIFE® PROCEDURE

 

The total radiation dose (which is measured in Greys, expressed as Gy) delivered in external beam therapies for prostate cancer is fractionated i.e. divided into smaller doses. This means that the treatment is usually spread over a relatively long period, normally once a day, five days a week for seven weeks. The intention behind this approach is to limit damage to organs other than the targeted prostate gland.

With the advance that has been made in more accurate tracking and aiming methods to deliver the therapy there has been a move in some quarters to deliver what is termed a hypofractionated radiation dosage. This means that the prostate gland and cancerous tumors associated with it are given higher individual doses (hypofractionated doses) of radiation over fewer treatments with a lower total dose of radiation. The theory is that such a procedure may offer better results, because it creates a greater differential between the prostate and normal tissue, i.e. is more brutal to the cancer and kinder to the normal tissue that is irradiated. There is considerable disagreement among scientists and radiation oncologists about the efficacy and long-term side effects of this procedure.

The potential benefits of hypofractionation are two fold. For the man receiving the therapy, there is the convenience of having many fewer sessions of treatment; for the facility providing the procedure there is the benefit of a higher turnover of patients.

CyberKnife® is a procedure which gained FDA approval in 1991 and which has a good record in certain tumors (e.g. nervous system). But it took many years before it was accepted for the treatment of prostate cancer. As late as February 2008 it was generally regarded as 'experimental' for prostate cancer because there were very few studies and no long term studies as to its efficacy and morbidity results.

The potential benefits
of CyberKnife® are based on the sophisticated tracking of prostate position - it is claimed that the stereotatic heads with the use of fiducials can track very small movements of the prostate and deliver doses more accurately than other methods. This sophisticated method of tracking prostate location may be particularly necessary because the patient has to lie for an hour or so for each CyberKnife® session. This contrasts, for example, with a session of conformal PROTON BEAM as currently practiced, where the sessions are a minute or so, hardly giving the prostate a chance to move..

Since the invention of CyberKnife®, a number of similar items have been developed with similar claims.

There is some evidence to support the idea of hypofractionation, but overall it cannot be denied that the procedure is experimental. Hypofractionation may well have merit, but long term (>10 year) results are not available for HDR BRACHYTHERAPY, which has been practiced since about 1997, and neither long nor short term (>5 year) peer reviewed results are yet available for CyberKnife®. Maybe in the long run this version will prove to have similar (but possibly not better) outcomes vis-a-vis non-hypofractionated EBRT (External Beam Radiation Treatment), in which case, its selling point will be convenience. Any man considering any
hypofractionated radiation therapy should make sure that his is a truly informed consent, and that he has chosen it over methods with established records.

There is a CYBERKNIFE FORUM That enables patients to get answers to questions from experts and share their own experiences. The forum is apparently run by a manufacturer of
Cyberknife® equipment , and should be considered in that light as should the fact that most of the responders appear to be men who have chosen this therapy. A feature of such single focus forums on the Internet is the firm belief that men who have chosen the therapy have made the only 'right' choice.