How does proton therapy compare with IMRT?

IMRT, short for intensity-modulated radiation therapy, is the standard X-ray radiation treatment used in cancer centres across Canada. Proton therapy is not available in Canada and is reached abroad. Many people want to know which one works better. Randomised trials have now compared the two in several cancers. The answer is not the same in every cancer, and some trials found no difference at all. This page reports what each trial found.

What is IMRT?

The letters stand for intensity-modulated radiation therapy. It uses X-rays, also called photons. The machine moves around the body and changes the strength of the beam as it goes. This shapes the high dose to match the shape of the tumour.

IMRT is the standard radiation treatment for most cancers in Canada. Every province has cancer centres that deliver it.

What is the difference between proton therapy and IMRT?

The difference is what the beam does after it reaches the tumour.

An X-ray beam passes all the way through the body. Tissue behind the tumour receives dose as the beam exits. IMRT lowers that exit dose by spreading it across a wider area at a lower level.

A proton beam stops at a set depth. Past that depth it gives almost no dose. This stopping point is called the Bragg peak, and it is explained on what proton therapy is.

A proton plan therefore puts less total radiation into the body. The trials were built to test whether that lower total dose changes what happens to the patient.

Does proton therapy work better than IMRT?

One finding repeats across the published trials. Tumour control and survival are similar with both treatments. Where the trials differ is on side effects, and there the results depend on the cancer. Some favour proton therapy, some show no difference, and a few favour IMRT.

The sections below give each cancer in turn.

What did the trials find in head and neck cancer?

Two large trials reported in 2026 and they did not agree.

A trial led by MD Anderson randomly assigned 440 patients with oropharyngeal cancer at 21 centres in the United States. Severe swallowing difficulty affected 34 percent of the proton group and 49 percent of the IMRT group. Severe dry mouth affected 33 percent and 45 percent. Feeding tube dependence at 60 days was 26.8 percent and 40.2 percent. Five years after treatment, 90.9 percent of the proton group and 81.0 percent of the IMRT group were alive. Severe skin reaction went the other way, affecting 24 percent of the proton group and 18 percent of the IMRT group.

The survival difference in that trial was a secondary result. The question the trial was designed to answer was whether proton therapy controlled the disease no worse than IMRT, and it did not do worse.

The British TORPEdO trial randomly assigned 205 patients at 20 National Health Service (NHS) hospitals in Britain. At 12 months, feeding tube dependence was 2 percent in both groups. Physical quality of life scores were 78.3 and 77.1, which is not a meaningful difference. Two years after treatment, 95 percent of each group was alive. Severe weight loss was recorded in 18 percent of the proton group and 6 percent of the IMRT group, a difference that did not reach statistical significance. The investigators concluded that in health systems where proton therapy is not already in routine use, IMRT remains the standard of care.

Both trials found the same rate of tumour control. They disagree on whether proton therapy adds anything beyond that.

What did the trials find in esophageal cancer?

A randomised trial at MD Anderson assigned 145 patients to proton therapy or IMRT. It measured total toxicity burden, a single score combining 11 side effects and surgical complications over the year after treatment. That score was 39.9 in the IMRT group and 17.4 in the proton group, about 2.3 times higher with IMRT. Among patients who went on to surgery, the complication score was 19.1 and 2.5.

Survival was the same. Three years after treatment, 50.8 percent of the IMRT group and 51.2 percent of the proton group were free of progression, and 44.5 percent of each group was alive.

What did the trials find in lung cancer?

Here the randomised result did not favour proton therapy. A trial at MD Anderson assigned 149 patients with locally advanced non-small-cell lung cancer to IMRT or proton therapy. Severe lung inflammation occurred in 6.5 percent of the IMRT group and 10.5 percent of the proton group. Local failure was 10.9 percent and 10.5 percent. The authors concluded that proton therapy gave no benefit in either measure.

That trial used passive scattering, an older way of delivering a proton beam. Most centres now use pencil-beam scanning, which shapes the dose more tightly, so the result may not describe treatment delivered today. A 2026 review pooled seven studies covering more than 240,000 lung cancer patients and found no difference in overall survival between the two treatments.

What did the trials find in prostate cancer?

Proton therapy is a long-established treatment for prostate cancer and tumour control is high. In the largest randomised comparison, five-year progression-free survival was 93.4 percent with proton therapy and 93.7 percent with IMRT. Both treatments work.

A proton beam gives no dose beyond its target, so less total radiation reaches the body. Proton centres report that this helps reduce side effects. In the randomised comparison, bowel, urinary and sexual function were measured by patient self-report, and no measurable difference was found between the two treatments. Those results were presented at a scientific meeting in 2024 and have not yet appeared in a peer-reviewed journal. A separate study published in 2025, which was not randomised, found less bowel worsening after proton therapy, at 26 percent compared with 47 percent, and no difference in urinary symptoms.

So proton therapy is not worse in these areas, and an advantage over IMRT has not yet been demonstrated. The American Society for Radiation Oncology places prostate cancer in the group where it recommends coverage within a clinical study or a registry. Which treatment suits you is a decision for your radiation oncologist.

What did the trials find in breast cancer?

RADCOMP is the first randomised trial to compare the two treatments in breast cancer. Its design has been published. Its main results have been presented at a scientific meeting but have not yet appeared in a peer-reviewed journal, so this page does not report them.

A 2026 study of 8,189 patients treated in routine care found skin reaction of any grade in 82.0 percent of those treated with protons and 57.1 percent of those treated with X-rays. Moderate skin reaction was less common after protons, at 13.4 percent compared with 20.9 percent. That study was not randomised.

Where is proton therapy the established choice?

Some uses do not rest on a head-to-head trial. They rest on the physics and on long-running clinical series. Health technology reviews and professional bodies agree on these:

• Tumours at the base of the skull, such as chordoma and chondrosarcoma.
• Tumours of the brain and spinal cord.
• Some eye tumours.
• Solid tumours in children treated with the aim of cure.
• Re-treatment where the total dose to a critical structure would otherwise be too high.

In these situations the tumour sits next to tissue that cannot be protected well with X-rays. Ontario Health’s review of proton therapy found that it may work as well as standard radiation with fewer side effects, and was clearest about children with brain tumours.

Who decides which treatment you receive?

Your radiation oncologist decides. The choice depends on where the cancer is, what sits beside it, your age, and what the treatment is trying to achieve. No website can tell you which treatment is right for you.

If you are considering proton therapy abroad, your provincial or territorial health plan decides whether it will pay. That is a separate decision, made by the plan rather than by a physician. See check funding in your province.

Frequently asked questions

Sources for this page (12)▸

1. Head and neck randomised trial, survival and side effect rates: Frank SJ, Busse PM, Lee JJ, et al., Proton versus photon radiotherapy for patients with oropharyngeal cancer in the USA: a multicentre, randomised, open-label, non-inferiority phase 3 trial, Lancet 2026;407(10524):174-184, doi:10.1016/S0140-6736(25)01962-2, PMID 41391462. doi.org (checked 2026-08-16)
2. TORPEdO trial, feeding tube dependence, quality of life, weight loss and the conclusion on standard of care: Thomson DJ, Price JM, Tyler M, et al., Proton beam therapy for oropharyngeal cancer (TORPEdO): a phase 3, randomised controlled trial, Lancet 2026;407(10535):1259-1275, doi:10.1016/S0140-6736(26)00314-4, PMID 41875914. doi.org (checked 2026-08-16)
3. Esophageal cancer, total toxicity burden, postoperative complication score, three-year progression-free and overall survival: Lin SH, Hobbs BP, Verma V, et al., Randomized Phase IIB Trial of Proton Beam Therapy Versus Intensity-Modulated Radiation Therapy for Locally Advanced Esophageal Cancer, J Clin Oncol 2020;38(14):1569-1579, doi:10.1200/JCO.19.02503, PMID 32160096. doi.org (checked 2026-08-16)
4. Lung cancer, severe lung inflammation and local failure rates, passive scattering delivery: Liao Z, Lee JJ, Komaki R, et al., Bayesian Adaptive Randomization Trial of Passive Scattering Proton Therapy and Intensity-Modulated Photon Radiotherapy for Locally Advanced Non-Small-Cell Lung Cancer, J Clin Oncol 2018;36(18):1813-1822, doi:10.1200/JCO.2017.74.0720, PMID 29293386. doi.org (checked 2026-08-16)
5. Lung cancer, pooled analysis of seven studies and no difference in overall survival: Fang CC, Chen WC, Tsai MS, Chen MF, Proton versus photon radiotherapy for non-small cell lung cancer: updated evidence from a systematic review and meta-analysis, Cancers 2026;18(3):453, doi:10.3390/cancers18030453. mdpi.com (checked 2026-08-16)
6. Prostate cancer, five-year progression-free survival and patient-reported bowel, urinary and sexual function, presented at a scientific meeting and not yet published in full: Efstathiou JA, Yeap BY, Michalski JM, et al., Prostate Advanced Radiation Technologies Investigating Quality of Life (PARTIQoL): Phase III Randomized Clinical Trial of Proton Therapy vs IMRT for Localized Prostate Cancer, Int J Radiat Oncol Biol Phys 2024;120(2S), abstract LBA01, ASTRO Annual Meeting, 30 September 2024. redjournal.org (checked 2026-08-16)
7. Prostate cancer, bowel and urinary quality of life in a study that was not randomised: Gergelis KR, Bai M, Ma J, et al., Long-Term Patient-Reported Bowel and Urinary Quality of Life in Patients Treated with Intensity-Modulated Radiotherapy Versus Intensity-Modulated Proton Therapy for Localized Prostate Cancer, Curr Oncol 2025;32(4):212, doi:10.3390/curroncol32040212. doi.org (checked 2026-08-16)
8. Proton centres report that lower total radiation dose helps reduce side effects in prostate cancer: University of Florida Health Proton Therapy Institute, prostate cancer. floridaproton.org (checked 2026-08-16)
9. Prostate cancer placed in the group recommended for coverage within a clinical study or registry, and the list of established uses: American Society for Radiation Oncology, Model Policies: Proton Beam Therapy, approved June 2017. astro.org (checked 2026-08-16)
10. Breast cancer, RADCOMP trial design: Bekelman JE, Lu H, Pugh S, et al., Pragmatic randomised clinical trial of proton versus photon therapy for patients with non-metastatic breast cancer: the Radiotherapy Comparative Effectiveness (RadComp) Consortium trial protocol, BMJ Open 2019;9(10):e025556, PMID 31619413. doi.org (checked 2026-08-16)
11. Breast cancer, skin reaction rates in 8,189 patients treated in routine care: Yu CC, Hsieh CC, Huang YT, et al., Toxicity profiles of proton and photon radiotherapy in postoperative breast cancer: a 10-year real-world cohort study, Breast Cancer Res 2026;28:49, doi:10.1186/s13058-026-02227-6. doi.org (checked 2026-08-16)
12. Proton therapy may work as well as standard radiation with fewer side effects, clearest in children with brain tumours: Ontario Health (Quality), Proton Beam Therapy for Cancer in Children and Adults: A Health Technology Assessment, Ont Health Technol Assess Ser 2021;21(1):1-142, PMID 34055109. pmc.ncbi.nlm.nih.gov (checked 2026-08-16)

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Every statement on this page is drawn from the sources listed below. Last updated: 16 August 2026.

This page is for general information only. It is not medical advice and it is not a decision about your care or your funding. Only your treating physician can advise you on treatment. Only your provincial or territorial health plan can decide whether it will fund treatment outside the country. protontherapy.ca is an information resource by Maple Med Global (MMG Medical Tourism Inc.), Toronto, Canada. We are not a hospital, a clinic, or a government body, and we do not provide medical care.