Very young cancer patients can particularly benefit from radiotherapy using protons. Fortunately, the Center for Proton Therapy at PSI has gained considerable experience in this field over the past two decades: its specialist expertise is in demand from children’s cancer clinics throughout Switzerland.
The six-year-old boy on the patient bed sleeps deeply and soundly. A stiff plastic mesh in the shape of his head prevents him from moving in his sleep. The rotating irradiation device, called a gantry, is already aligned with the boy’s head. The PSI radiology specialist checks one last time to be sure the child is lying correctly, then leaves the room. From the control room next door, she starts the proton beam.
Now the gantry’s irradiation head emits a concentrated beam of protons and scans the tumour in the little patient’s brain with millimetre precision. The high-energy particles destroy the genetic substance in the cancer cells, killing them. Proton therapy functions on the same principle as classic radiation therapy in hospitals, where X-rays are used. But protons have a crucial advantage over X-rays: they release most of their energy in a very narrow area in the body, within the tumour itself – where they essentially get lodged. Thus the healthy tissue surrounding the tumour is protected and is less likely to be damaged than in classic radiation therapy.
Children with cancer can especially benefit from proton therapy, explains Damien Weber, chief physician and head of the Center for Proton Therapy at PSI. “Children are still growing, and if healthy cells close to the tumour get damaged during radiation therapy, they can pass this damage along to more and more cells with every future cell division.” Besides that, the likelihood of damage to a critical structure near the tumour, such as the spine or brain, is much higher in a small body than in the larger body of an adult.
Therefore children run a higher risk that conventional radiotherapy for cancer will cause long-term damage from which they will suffer for the rest of their lives, ranging from tumours that only develop as a result of the radiation, to hearing loss, impaired growth and learning disabilities. “If a child in Switzerland needs targeted radiation therapy against cancer, the irradiation method of choice is almost always this very precise proton therapy,” says Damien Weber.
A success story
The Center for Proton Therapy has been treating young cancer patients since 1999. In 2004, for the first time, a small child was irradiated under anaesthesia: just over two years old, the patient suffered from a soft tissue tumour in the eye socket.
Unlike adults, such very small patients require anaesthesia. “Precise irradiation such as proton therapy is pointless if the person moves during the treatment,” Damien Weber explains. “But small children find it extremely difficult to keep still during the entire irradiation period.” Light anaesthesia ensures the children sleep and lie still while the tumour-destroying proton beam does its work. Overall, around half of all children and adolescents up to the age of 18 are irradiated under anaesthesia.
Since 2004, there has been close cooperation between the Center for Proton Therapy and the Department of Anaesthesia at the University Children’s Hospital of Zurich. This collaboration guarantees the presence of a senior physician and anaesthesia nurse from the Children’s Hospital at PSI every day: they initiate the anaesthesia, monitor the condition of the little patients, change bandages and generally ensure the best possible care.
“We take a lot of time for the children,” says Ilka Schmidt-Deubig, senior anaesthesiologist at the Children’s Hospital of Zurich. “They shouldn’t encounter a typical hospital atmosphere here with us.” That’s why the team always books appointments so that the parents and the child can arrive in a calm setting, at least half an hour before the radiation treatment, in a playroom specially set up for this purpose. “Even traumatised children have come to trust us after one or two weeks.”
At the start of the cancer treatment, the children receive a string with their first names spelled out in colourful letter beads. “Over the course of the cancer treatment, more and more beads are added, the courage beads,” Ilka Schmidt-Deubig explains. For example, when the port catheter, through which the anaesthetist introduces medication, is inserted; a therapy band before the irradiation; an austerity band because the child may not eat or drink anything before the anaesthesia – not always easy if you’re hungry or thirsty.
Every year 60 to 70 children and adolescents are treated at PSI; in all, there have been more than 800 to date. The majority of all these young patients suffer from tumours of the brain and spinal cord. The second most common are sarcomas, which are cancers that develop in connective, supportive or muscle tissue
National centre of excellence for Switzerland
“Cancer treatment in children who require anaesthesia during irradiation calls for more planning,” says Katrin Scheinemann, head of Paediatric Haematology and Oncology at the Children’s Hospital of Eastern Switzerland in St. Gallen. “We are all the more glad that PSI offers such a highly specialised irradiation centre with so much experience. Compared to other countries, we have one of the oldest proton centres anywhere, also with a focus on treating children with radiation.»
Katrin Scheinemann is president of the Swiss Paediatric Oncology Group (SPOG), a network of all nine centres in Switzerland with a children’s oncology department. In addition to the Children’s Hospital of Eastern Switzerland in St. Gallen, this network includes the university hospitals in Bern, Basel, Zurich, Lausanne and Geneva as well as the children’s hospitals in Lucerne, Aarau and Bellinzona. As a nonprofit organisation, SPOG coordinates and takes responsibility for clinical studies and research programmes on cancer in children and adolescents throughout Switzerland.
One thing is guaranteed: the young patients are always treated in accordance with international protocols. “So it doesn’t matter which of the nine centres the parents take their children to for treatment – they get the same – i.e. the highest quality - therapy everywhere.”
PSI treats around 70 percent of all children in Switzerland who need targeted radiation therapy. This makes the Center for Proton Therapy the country’s largest radiation treatment centre for children.
Hopeful prospects
The six-year-old boy has come through the radiation treatment successfully; the tumour in his brain was scanned with high-energy protons for around 20 minutes. The radiology specialist removes the face mask and takes the little one, who is still sleeping, to the recovery room, where his parents are already waiting. Here he can recover in peace as he fully wakes up.
The next irradiation session follows on the next day: for a total of six weeks, Monday to Friday. This is not an easy time for the children and their parents. But there is hope: the chances of curing childhood cancer have improved significantly in recent decades. According to the Swiss Childhood Cancer Registry, Switzerland’s ten-year survival rate for children diagnosed between 1989 and 1998 was 76 percent – 20 years later, between 2009 and 2018, it had already risen to 85 percent. These numbers are expected to improve again over the next ten year period. And the treatment provided at PSI’s Center for Proton Therapy is certainly contributing to this success story.
Text: Brigitte Osterath
Pioneering studies
In addition to the paediatric studies it participates in, PSI also takes part in clinical studies on cancer treatment for adults. Currently participants are being sought for the European clinical study PROTECT, in which PSI is taking part jointly with the Clinic for Radio-Oncology at the University Hospital of Zurich. PROTECT compares side-effects of conventional radiation therapy for oesophageal cancer with those associated with proton therapy. If the clinical study yields evidence that proton therapy also offers advantages for treating this type of cancer, patients could routinely be treated at PSI. Oesophageal cancer would be permanently added to the Federal Office of Public Health list of indications, and health insurance providers would cover the costs of proton therapy.