“Even more cancer patients could benefit from proton therapy”

The book Physics Against Cancer, recently published in German as Mit Physik gegen Krebs, describes how the Paul Scherrer Institute PSI developed a trailblazing technology for the treatment of tumours: proton therapy. It is thanks to the pioneering spirit and perseverance of several researchers at PSI that this groundbreaking radiation method is available to us today. Every year it saves the lives of many children and adults with hard-to-treat tumours. But even more people could benefit from it, says Damien Weber, head and chairman of the Center for Proton Therapy at PSI, in an interview.

Professor Weber, what makes proton therapy so groundbreaking that it warranted writing a book about how it was developed at PSI?

Damien Weber: Just like the X-rays used in conventional radiotherapy in hospitals, irradiation with protons destroys the genetic material in cancer cells, so that they die. But protons are particles and, when used in radiation therapy, release most of their energy in just a narrow area within the body – that is, in the tumour itself. In effect, they get stuck there. Therefore, a higher dose of radiation can be administered to the tumour while protecting the healthy tissue behind it. 

However, it has to be possible to control the proton beam very precisely during irradiation, and this capability requires a lot of technology and took a few decades to develop. We needed to guarantee, ultimately, that the method is 100% safe for patients.

What are the advantages of proton therapy for patients?

If cancer patients are irradiated with protons instead of X-rays, they have a lower risk of experiencing certain side effects that often accompany radiation. This is especially true for tumours that are located next to sensitive tissues or organs, such as brain tumours, ENT tumours, and tumours in the head and neck area, at the base of the skull or near the spine.

In the case of ENT tumours, for example, irradiation of the oral cavity and the pharyngeal mucosa with X-rays can cause permanent damage to the swallowing muscles, meaning in some cases that the patient can no longer eat normally.

Depending on the type of cancer, conventional radiation therapy can also cause damage to the salivary glands or the pituitary glands. And of course, children with cancer in particular benefit from proton therapy.

Why children?

In children, the risk that radiation can damage healthy tissue and thus lead to long-term damage is higher because they are more sensitive to radiation than adults. This is because if healthy cells that were close to the tumour are damaged during radiation therapy, they can pass this damage on to more and more cells with each cell division. In addition, in a child’s small body, the probability that a critical structure such as the spine or brain is located near the tumour is simply much higher than in the larger body of an adult. Therefore, it is particularly advantageous to use a radiation method with the high precision of proton therapy for children with cancer.

What are the greatest successes that helped make it possible for proton therapy to become established as a clinical treatment method in Switzerland?

The first high point was in 1984, when a patient was irradiated with protons at PSI for a rare form of eye tumour − the first time in all of Europe. Then in 1996, we irradiated the first patient using the spot-scanning technique we had developed, a method that scans deep-seated tumours with a pencil-thin proton beam – as if you were erasing them. That was a world’s first at the time! 

2001 was also a significant year for proton therapy: since then, health insurance companies in Switzerland have covered the costs for treating certain types of cancer. In 2004, the first small child was irradiated under anaesthesia here. Thanks to our collaboration with the Children's Hospital Zurich, we now treat around 60 to 70 children and adolescents every year.

Another important year was 2007. That's when the Center for Proton Therapy got its own accelerator, called COMET. Before that, the protons for irradiation were generated in an accelerator that PSI used, and still uses, mainly for physics experiments. That accelerator needs to be shut down for several months a year for maintenance purposes. We can use COMET to irradiate patients from Monday to Friday all year round.

Does that mean you’ve reached your goal?

No, unfortunately not. Even more cancer patients could benefit from proton therapy than is currently the case − not only worldwide, but also here in Switzerland. One problem is that the full potential of proton therapy is not yet well enough known in all specialist circles. As a result, many cancer patients who would be eligible for proton therapy do not even know that this option exists.

We currently treat more than 170 patients with deep-seated tumours each year, but we actually have the capacity for more. Some cancer patients who could benefit from proton therapy end up opting for conventional radiation therapy in their local hospital.

What stops people from taking advantage of proton therapy when the treatment for many types of cancer is even covered by health insurance?

We are the only facility for proton therapy in Switzerland, and the journey to Villigen can be long and arduous, especially for people from French-speaking Switzerland, Ticino, or eastern Switzerland. The therapy usually lasts several weeks. Some patients rent a room near the PSI Center for Proton Therapy for this period. Unfortunately, health insurance companies do not currently cover the accommodation costs, and this probably prevents some people from coming to us for treatment. Basically, it is time to set up more proton therapy facilities in Switzerland. Such ideas have been raised several times, but unfortunately, they have never been pursued further.

Do we even know for certain, then, that the effort involved in proton therapy is worth it?

Yes, clinical studies clearly show that proton therapy can be advantageous compared to conventional radiation. For example, in the case of ENT tumours, this is particularly true for unilateral head and neck tumours, as well as for advanced tumours in the nasopharyngeal region or in the paranasal sinuses. Another example is brain and spinal tumours. But it's true: there is still a lack of hard data on many other types of cancer, because clinical trials are expensive and, above all, time-consuming. The results, therefore, are only coming in gradually.

Are clinical trials the only way to get such data?

No, there are alternatives. Colleagues at the University Medical Center Groningen in the Netherlands have now developed an approach to compare proton therapy with conventional radiation therapy without clinical trials. To do this, they simulate on the computer which side effects, and how many, can be expected after treatment with one method or the other – for example, how much damage is done to the swallowing muscles. They then track the actual side effects of patients who have been irradiated in one way or another and continually adapt their model.

What has been shown so far: proton therapy appears to have even fewer side effects for tumours in the head and neck area than we originally expected. So, it looks as if the effort required for proton therapy is actually even more worthwhile than we previously thought. In the long term, this can make a big difference in the quality of life for those who have recovered.

At present, proton therapy still seems to be a niche application that is only used for a few types of tumours. Will this change in the future?

We are working on that. In collaboration with the radio-oncology specialists at the Aarau Cantonal Hospital, we have just selected patients for an international lung cancer study. Within about three years, we expect to have results indicating whether proton therapy significantly extends life expectancy in advanced lung cancer compared to conventional radiation therapy.

Also, we are currently investigating whether proton therapy has advantages in the treatment of oesophageal cancer. We are participating in this clinical study – within the framework of a European collaboration − together with the radio-oncology clinic at the University Hospital of Zurich. But here too, it is difficult to find study participants, for the same reasons I mentioned earlier. We are constantly looking. Patients who think they might be suitable for the study are welcome to contact us.