Proton beam therapy is an advanced form of radiation therapy that delivers sub-millimetre accuracy in targeting cancer tumours, while minimising damage to surrounding healthy tissue. It is used in the treatment of a wide range of cancers.
Unlike traditional radiation therapies that use X-rays (photons) or other high-energy sources, proton beam therapy uses high-energy protons to destroy cancer cells. Sometimes referred to as particle therapy, this approach is distinguished by its ability to deliver radiation precisely to the tumour, sparing surrounding healthy tissues.
This enhanced precision offers particular benefits for patients across various cancer types, especially those where the tumour is located near critical structures or organs or in paediatric patients, where long-term side effects are a greater concern.
The history of proton beam therapy
Proton beam therapy was first used in a research setting in 1955 in Berkeley, California. While early outcomes were promising, it wasn’t until advancements in imaging technologies, such as CT, MRI and PET scans, that healthcare professionals could fully leverage the precision of protons. These innovations allowed for accurate visualisation of tumour location, size and shape, enabling precise treatment planning. The first hospital-based proton therapy centre in the United States opened at Loma Linda University Medical Center in 1990.
As of 2025, approximately 110 proton therapy centres are in operation worldwide, and more than 250,000 patients have been treated with proton therapy globally.
Proton International London is part of a wider network of proton therapy centres operated by Proton International, the majority of which are currently based in the United States.
As more patients are treated, both across our network and globally, clinical evidence continues to grow, supporting the use of proton beam therapy as an effective treatment for a broad range of indications.
Proton beam therapy clinical studies
Please find below a selection of clinical studies relevant to proton beam therapy and the cancer indications managed at our London centre.
Head and neck cancer
Int J Part Ther. 2021 Jun 25;8(1):84-94. doi: 10.14338/IJPT-20-00071.1. PMID: 34285938; PMCID: PMC8270078.
The Particle Therapy Cooperative Group (PTCOG), an international consortium of experts in proton therapy, published a consensus statement detailing the increasing importance and current position of proton therapy in the treatment of head and neck cancers. They highlighted the growing volume of evidence establishing proton therapy as a treatment option in several subsites of the head and neck: nasopharynx, sinonasal, oropharynx, postoperative, and reirradiation, while emphasizing the need for ongoing research into this important area.
JCO 42, 6006-6006(2024). DOI:10.1200/JCO.2024.42.16_suppl.6006.
This landmark phase III, multi-institutional randomized trial carried out across the USA compared intensity modulated proton therapy (IMPT) versus standard photon intensity modulated photon therapy (IMRT) in the delivery of chemoradiotherapy in 440 patients with oropharyngeal cancer (mostly tonsil and base of tongue tumours). While many previous retrospective reports have indicated that IMPT is as effective as IMRT but with fewer side effects, this is the first large trial aiming to prove this. This trial provides high quality robust evidence that IMPT is more effective than IMRT in preserving swallowing function/nutrition and reducing feeding tube rates during radiotherapy, and increasing the speed of patients recovering and returning to normal function/work once radiotherapy is complete. IMPT cure rates are the same as for IMRT, and there is some evidence to suggest that survival rates at 5 years after radiotherapy are higher for IMPT compared with IMRT. Overall, the trial is showing that IMPT is at least of equivalent effectiveness to IMRT, but with less side effects and quicker recovery after treatment.
Int J Radiat Oncol Biol Phys. 2019;105(1s).
This is a paper summarising the experience at MD Anderson, a large very experienced proton centre in USA, of treating patients with head and neck cancer with proton therapy. They report on 573 patients treated over a 12 year period, with a range of different cancers including oropharynx, paranasal sinuses, and peri-orbital tumours (close to the eye). They report that proton therapy is effective at controlling head and neck cancers, with good long term survival. In addition the side effects (acute and late toxicities) after proton therapy were felt to be acceptable. The authors conclude that their results support proton therapy as a standard and effective treatment option for head and neck cancer.
Radiother Oncol. 2016 Jul;120(1):48-55. doi: 10.1016/j.radonc.2016.05.022. Epub 2016 Jun 21. PMID: 27342249; PMCID: PMC5474304.
This study reports on a case matched retrospective analysis where 50 patients treated with intensity modulated proton therapy (IMPT) were matched with 100 comparable photon intensity modulated radiotherapy (IMRT) patients treated in the same hospital over the same time period, to compare effectiveness and side effects of the two treatments. The two treatments were equally effective in controlling the tumours and for long term survival. However, IMPT was associated with reduced rates of patients needing feeding tubes for nutritional support, and of severe weight loss, suggesting that IMPT was having less of an impact that IMRT in terms of maintaining nutrition during and after treatment.
JAMA Netw Open. 2022 Nov 1;5(11):e2241538. doi: 10.1001/jamanetworkopen.2022.41538. Erratum in: JAMA Netw Open. 2022 Dec 1;5(12):e2250485. doi: 10.1001/jamanetworkopen.2022.50485. PMID: 36367724; PMCID: PMC9652753.
This is a large study looking back at the treatment results of oropharyngeal cancer patients, comparing 58 patients treated with intensity modulated proton therapy (IMPT) and 234 patients treated with standard photon intensity modulated radiotherapy (IMRT). The two treatments were equally effective in controlling tumours and for long term survival. However, the rates of acute side effects happening during treatment including pain, dry mouth, mouth ulcers, difficulty swallowing, altered taste, feeling sick, and weight loss were all significantly less for the IMPT patients. In the longer term, IMPT patients experienced less dry mouth, and fewer patients needed a feeding tube for more than 6 months. Overall the authors concluded that IMPT was as effective as IMRT, but was associated with less acute and longer term sides effects. They also highlighted that because this was a retrospective study that can have biases affecting results, it is important that further research and clinical trials are done to provide more evidence for the benefit of proton therapy for these patients.
Lancet Oncol. 2014 Aug;15(9):1028‑1038.
This large study has drawn together 41 published observational retrospective studies of patients with paranasal sinus and nasal cavity cancers treated with particle therapy (which includes proton therapy) or photon therapy, pooling the results in a meta-analysis of all of these studies to compare the two different treatments. The analysis included 286 patients treated with particle therapy and 1186 patient treated with photon therapy, and showed that those treated with particle therapy had better long term tumour control and survival that the photon patients. Because there was a lot of variability in the individual studies, the authors concluded that it will be important to further research this area in the future by collecting outcomes of treatment and side effects prospectively, to understand whether the suggested benefits in this meta-analysis of particle therapy for patients with paranasal sinus and nasal cavity cancers are realized.
About proton beam therRadiother Oncol. 2025 Jan;202:110648. doi: 10.1016/j.radonc.2024.110648. Epub 2024 Nov 23. PMID: 39586359.
This study carried out in Taiwan reports on a case matched retrospective analysis where 276 patients treated with intensity modulated proton therapy (IMPT) were matched with 276 comparable photon intensity modulated radiotherapy (IMRT) patients treated in the same hospital over a 5 year period, to compare effectiveness and side effects of the two treatments. The results showed that patients treated with IMPT had better long term survival than those treated with IMRT, and reduced the risk of disease recurrence. In addition the IMPT patients had less acute side effects and less need for placement of feeding tubes during treatment. Because retrospective studies can have bias affecting results, the authors say that while the results are very promising, more research is needed to confirm this promise.