Proton beam therapy is less well-known than conventional radiotherapy, largely because it’s a newer technology and is used in more targeted cases, where reducing side effects and protecting healthy tissue is crucial to quality of life. It does so by using high-energy protons precisely to the tumour, sparing surrounding healthy tissues.
For more information about what proton therapy treatment is, its benefits and how it works, please see the What Is Proton Beam Therapy? page and explore our news section.
The history of proton beam therapy
Proton beam therapy was first explored in a research setting in 1955 at Berkeley, California. The early results were very encouraging, but the technology of the time couldn’t yet deliver on its full promise.
That changed with the introduction of advanced imaging techniques like CT, MRI, and PET scans, which show tumours in finer detail and allow clinicians to pinpoint their exact size, shape, and location. From then on, it became possible to carry out proton therapy with remarkable precision.
In 1990, proton therapy took a major step out of the lab and into the clinic. The first hospital-based centre opened at Loma Linda University Medical Center, marking the beginning of a new era in cancer care.
As of 2025, there are around 110 proton therapy centres worldwide that have treated approximately 250,000 patients. Proton International London is proud to be one of only two centres in the UK. We are part of a wider network of proton therapy centres operated by Proton International, the majority of which are based in the United States.
As the number of proton beam therapy patients continues to grow, so does the body of clinical evidence. Each new case study and research paper enhances our understanding of proton therapy and its effectiveness in treating various types of cancer.
The research studies presented below provide reassuring evidence of proton therapy’s safety, its effectiveness as a cancer treatment, and its usefulness in minimising long-term side effects.
Proton beam therapy clinical studies
We have collated a selection of clinical studies about proton beam therapy, which we hope you find reassuring and helpful. These studies are particular to head and neck cancer, as this is where a large percentage of research has been conducted. We hope to publish more papers about other cancer types soon. If you have any questions, please contact our helpful and knowledgeable team.
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.