Radiotherapy is one of the most widely used treatments in the fight against cancer. It uses high-energy radiation to destroy tumour cells or inhibit their growth. In recent years, however, proton therapy has emerged as a promising technology, offering greater precision in radiation delivery.
How does proton therapy work? Difference between protons and photons
The main difference between proton therapy and conventional radiotherapy lies in the type of particles used. Conventional radiotherapy uses beams of photons (X-rays), whereas proton therapy uses protons, the positively charged particles found in the nuclei of atoms.
This difference has important consequences. As photons pass through the body, they deposit energy along their path, both before and after the tumour. By contrast, protons deposit most of their energy at a highly localised point along their path, corresponding to the tumour location. This substantially reduces the radiation dose delivered to the healthy tissues both surrounding and beyond the treatment site.
As shown in the images, the difference in dose distribution is striking. In both brain tumours and more complex treatments, such as craniospinal irradiation, proton therapy achieves greater dose concentration within the target area while limiting radiation exposure to healthy organs.
Main advantages of high-precision proton therapy
One of the main advantages of proton therapy is what specialists refer to as an “ideal dose profile”. This means the radiation dose required to treat the tumour can be delivered while minimising the integral dose received by the rest of the body. This is particularly important in paediatric patients and in tumours located close to highly sensitive structures, such as the brain, spinal cord or eyes.
Although it has potential benefits, its considerable technological complexity means proton therapy is not yet widely available. Protons are approximately 1,800 times more massive than electrons and so require large, highly sophisticated particle accelerators.
The proton beams are produced by accelerators such as cyclotrons or synchrotrons, which accelerate protons to very high velocities before directing them precisely towards the patient. Advanced beam delivery systems are also required to ensure the treatment corresponds to the exact shape of each tumour.
When is proton therapy indicated?
It is generally agreed that the question is not whether proton therapy is superior to conventional radiotherapy, but which patients are most likely to derive genuine clinical benefit from it. Each case requires an individualised assessment of factors such as tumour type, tumour location and patient characteristics before a final treatment decision is made.
Catalonia is working to incorporate this technology into its public healthcare system. The Catalonia Proton Therapy Project includes the establishment of the Catalonia Proton Therapy Centre, which will form part of a regional care network serving the entire territory. Installation of the equipment is scheduled for 2027–2028, with the first patient expected to be treated in the final quarter of 2028. This progress is reinforced by European research initiatives such as the EMPATHY (PIANOFORTE) project, aimed at continuing to improve proton therapy techniques.
The future of cancer treatment
Ultimately, proton therapy represents a significant advance in radiation oncology. Its high precision makes it possible to treat selected tumours while reducing radiation exposure to healthy tissues, with the potential to improve patients' quality of life. Although it is unlikely to replace the vast majority of current treatments, it is expected to become a valuable component of personalised cancer medicine.
Information documented by:
Dr Carles Gomà, Consultant in Medical Physics | Hospital Clínic Barcelona
