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New radiotherapy techniques tested in clinical trials.

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Radiotherapy for prostate cancer is constantly being improved. Some of these modifications involve giving a higher dose of radiation over a shorter time-period. Although the outcomes are similar, this reduces the number of treatments for the patient and frees up healthcare resources. This week’s blog describes the latest clinical trial results for ultra-hypofractionated radiotherapy for prostate cancer.

Different types of prostate radiotherapy

Research has led to constant improvement in the way radiotherapy is delivered, making it safer and more effective. Subsequently, there are different types of radiotherapy for prostate cancer that have been used over the years. Keeping track of the names of these therapies is challenging. There are two broad categories of radiation treatment for prostate cancer. One is brachytherapy, where radioactive seeds are inserted into the prostate. The other is external beam radiation therapy (EBRT). During EBRT, a linear accelerator directs beams of radiation into the prostate at different angles. The beam is specifically targeted to match the man’s prostate shape and position in the body. The aim is to maximise the radiation dose to the tumour and minimise damage to the surrounding areas.

A typical “conventional” treatment plan consists of treatment five times per week over 7.5 weeks. Conventional radiotherapy has been improved over the years with new technological advances. 3D-conformal radiotherapy (3DCRT) allows more accurate targeting of the prostate tumour by using three-dimensions to focus the beam. Another improvement on EBRT is intensity-modulated radiation therapy (IMRT). IMRT allows more accurate targeting of the shape of the prostate or the tumour. IMRT is very commonly used in Australia.

Hypofractionation is another improvement on conventional EBRT. Hypofractionated treatment delivers a higher dose of radiation over a shorter overall treatment time than conventional fractionation. In other words, the same total amount of radiation is delivered, in higher doses, over fewer visits to the clinic. Recent clinical trials (such as CHHiP and PROFIT) have shown that prostate radiotherapy has similar outcomes and side effects if it’s delivered in higher doses over fewer visits. For example, radiation in higher doses over 20 visits instead of 37 visits can be equally successful.

Hypofractionated radiotherapy is becoming a recommended form of radiotherapy for localised prostate cancer. Guidelines from the US recommend that men with early-stage prostate cancer be offered hypofractionated radiotherapy if appropriate. The advantages of hypofractionation are less visits and less overall treatment time for men with prostate cancer. Additionally, less visits frees up resources in the health sector, hopefully reducing waiting times and costs for taxpayers.  

Ultra-hypofractionation

A recent new technology uses an extreme form of hypofractionation. During this procedure, radiation is delivered in even higher doses over an even shorter time period, such as one or two weeks. This radiotherapy is called Stereotactic Body RadioTherapy (SBRT) or Stereotactic Ablative Body Radiotherapy (SABR). CyberKnife was the first type of SBRT/SABR to be introduced into Australia. The name Cyberknife refers to the Cyberknife machine that delivers SBRT/SABR treatment. Now we have other types of SBRT/SABR machines, so it’s not always referred to as Cyberknife.

It’s very confusing having all these different names for the same type of treatment. In order to alleviate some of this confusion, another long and complicated word has been invented to refer to the SBRT and SABR: ultra-hypofractionation.

Comparing ultra-hypofractionation to other prostate cancer radiotherapy

Research around the use of ultra-hypofractionation (SBRT/SABR) was discussed in a research blog from last year. There have been a number of small trials testing ultra-hypofractionation for men with localised prostate cancer. These have promising results, showing that it has a good safety record and appears to be effective. But until now, there has been no randomised controlled trial – the highest level of evidence.  

Current important questions in this field of research are:

  • Is ultra-hypofractionated radiation as effective, or better than, conventional radiotherapy for prostate cancer?
  • Is it as safe as conventional radiotherapy for treating prostate cancer?
  • How does it compare to hypofractionated radiotherapy?

The HYPO-RT-PC trial

A new randomised controlled trial of ultra-hypofractionation has recently been published in the Lancet journal. This trial was performed in Sweden and Denmark by a group of collaborating clinicians and researchers. They were led by Prof Anders Widmark, of Umeå University in Sweden.

This trial, known as HYPO-RT-PC, compared ultra-hypofractionation to conventional IMRT for localised prostate cancer. Men joining this trial had either intermediate or high-risk prostate cancer, but no lymph node or metastatic tumours. Most of the men had intermediate risk cancer. HYPO-RT-PC is a phase 3 randomised controlled trial, conducted in 12 different treatment centres over two countries.

This trial design is known as a non-inferiority trial. The aim was to ask whether ultra-hypofractionation is not worse than the conventional treatment. This may sound a bit odd. What we want to know is whether men receiving conventional treatment could instead get ultra-hypofractionation, without it being less effective or less safe. Doctors could then advise men a new treatment is available that is much quicker, but still as effective and safe for them.

591 men received conventional radiotherapy (IMRT: the current standard treatment) for their prostate cancer. They were compared to 589 men receiving ultra-hypofractionation. The conventional radiotherapy consisted of 39 treatments (5 days a week for 8 weeks). Men having ultra-hypofractionation received 7 treatments of higher dose (3 days a week for 2.5 weeks).

Success of ultra-hypofractionation treatment

The trial followed-up these men for an average of 5 years to record the effectiveness of their treatment and their side effects. The main outcome measured was called failure-free survival. This was defined as men surviving with no increase in PSA or cancer progression (either new symptoms or new tumours on scans) The HYPO-RT-PC trial results showed:

  • 84% of men, in both groups, enjoyed failure-free survival over an average 5 years. These men did not see their cancer progress in that time period.
  • There was no significant difference in the overall survival rates of men in either group.

These results indicate that the new ultra-hypofractionation treatment is equally successful to the current standard treatment, IMRT. In clinical trial speak – the new treatment is non-inferior to the current standard.

Side effects from ultra-hypofractionation

Radiotherapy to the prostate can cause side effects such as problems with urination, bowel movements and erections. Not all men experience these problems. These side effects are often more serious at the time treatment finishes but improve with time. Unfortunately, some men see these problems appearing many years after their treatment.

Side effects in the HYPO-RT-PC trial were measured in two ways: as reported by the men in the trial, and as reported by their doctors. Overall, there was pretty good agreement between the men and their doctors regarding these side effects. These results showed:

  • There is some evidence of an increase in the rates of urinary and bowel side effects at the end of treatment (but not after) in the ultra-hypofractionated treatment group.
  • The rates of erection problems were similar between the two groups.

These results show a slight increase in the risk of urinary and bowel problems at the end of the ultra-hypofractionated treatment. No long-term differences were apparent. Since the radiation is given in much higher doses, over a shorter period of time, this increase in side effects was expected. This is useful information that will help men and their doctors to decide which treatment they would prefer.

What does this mean for Australian men?

There are different types of radiotherapy available for men with prostate cancer. Hypofractionation is becoming more popular, especially as new US guidelines recommend it be offered by doctors to appropriate men. But it takes a while for new technologies to become wide-spread. Expensive new machinery often needs to be installed and staff trained to perform new techniques. It also takes a long time to establish high-quality evidence on which to make recommendations.

The HYPO-RT-PC trial shows that, for men with intermediate-risk prostate cancer, ultra-hypofractionated radiation has the same outcomes and acceptable side effects compared to the current standard IMRT. So it’s a potential alternative treatment for these men. Unfortunately, what we don't yet know, is how hypofractionated and ultra-hypofractionated radiotherapy compare. So it’s currently difficult for men and their doctors to decide between hypofractionation and ultra-hypofractionation.

Hypofractionation and ultra-hypofractionation, are available in Australia. As for any type of radiotherapy, hypofractionated and ultra-hypofractionated radiotherapy are not suitable for every man. Your radiation oncologist is in the best position to advise what type of radiotherapy is suited to each man, based on his tumour and his own preferences, and to advise on the expected side effects.

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