Carbon Ion Therapy: The Particle Therapy Treatment That Packs a Powerful Punch

Radiation therapy is currently used to treat approximately 50% of all cancers (1). Conventional radiation therapy such as photons is not typically used for tumors that are considered radioresistant or recurrent diseases where radiotherapy has been used before. The rationale is that they are unlikely to effectively treat the cancer and would cause unnecessary damage to healthy tissue. This is where carbon ion therapy, with its unique characteristics might be able to help.

Physical and Biological Considerations

Carbon ions fall into the category of particle therapy, the same as protons. Protons have become more established in mainstream cancer treatments since their introduction in the 1940s and are recognized for their high precision targeting of tumors, healthy tissue sparing, and reduction in side effects of treatment (2).

Carbon ions share many similarities to protons in that both exhibit energy distribution at depth in the same characteristic pattern known as the “Bragg Peak”. This shows a slow initial absorbed dose as it passes through the tissue and then a very steep rise to maximum absorption, followed by a sharp fall towards the end of the particle range (3).

Carbon ions deposit the majority of their energy near the end of their trajectory through tissue as they decelerate. By selecting the appropriate beam energy in carbon ion therapy, the peak energy transfer can be aligned with the tumor, while adjacent healthy tissue receives minimal dose owing to the steep dose gradients (3).

Carbon ions differ from protons in a few ways. The lateral fall-off and penumbra (sharpness) for carbon ions are smaller than protons resulting in superior dose distribution. Carbon ions have a higher RBE (relative biological effectiveness) at 2-3.5 compared to protons’ RBE of 1.1. An important factor in radiation therapy is the oxygen enhancement ratio (OER). Tumors that are well-oxygenated typically have an OER of 1 for photons and protons, and they respond well to radiation treatments. Tumors that are deemed to have low radiosensitivity or poor oxygenation typically have high OER. To reduce this and effectively treat that tumor a high LET particle is needed. Fortunately, carbon ions have the highest LET out of photons, protons and electrons and are 12 times heavier than a proton. They also have an increased probability of direct cell death through double-strand break of DNA, unlike with photons, which require the generation of free radicals to damage the cell DNA. All these characteristics identify carbon ions as the most effective particle to treat hypoxic radioresistant tumors (4).

Current Carbon Ion Technology and Its Limitations

The first center to offer carbon Ions as a form of treatment was The National Institute of Radiologic Sciences in Japan in 1994. Clinical trials have continued to showcase the benefits of this treatment and its popularity has increased and to date five countries now offer it as a treatment option and more are planning installations of facilities to support carbon ion machines (5).

Carbon ions are produced using a synchrotron which accelerates the carbon ion particles to the speed and energy that is required for treatment. One of the main reasons that carbon ions are not globally accessible in the same way that photons are is the size and expense associated with them.

Carbon ion machines, particularly those with a rotating gantry, are very large and the equipment very heavy. Rotating gantries are approximately 11 meters in diameter, 25 meters in length and around 600 tons in weight (6). Housing these involves expensive construction work and requires a large space. Fixed beam carbon ion machines reduce these housing needs however, the use of a fixed beam with a standard supine treatment couch significantly limits the number of treatment beams achievable or requires the patient to change position multiple times during treatment delivery. This can result in patients not being considered for this treatment modality due to inferior dose distributions or treatment set ups being overly complicated and time-consuming.

A Potential Solution to Making Carbon Ions More Efficient and Accessible

Carbon ion therapy in an upright position could overcome a number of the limitations currently identified with this treatment option. An upright patient positioning system, such as ‘Eve’ produced by Leo Cancer Care, could allow existing fixed beam machines to deliver multiple treatment angles, including posterior beams, without the need to reposition the patient between each beam, improving treatment accuracy and significantly reducing treatment time. By removing the need for a rotating gantry, treatment rooms will be smaller and more compact and a more economically viable investment option for treatment facilities.

References

1. Baskar, R., et al. (2012). Cancer and Radiation Therapy: Current Advances and Future Directions. International Journal of Medical Sciences. ((3): 193-199. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3298009/
2. Park JM, Kim Ji, Wu HG. (2021). Technological Advances in Charged-Particle Therapy. Cancer Res Treat. 53(3):635-640. doi: 10.4143/crt.2021.706
3. Halclar, F., Ark, M. (2025). Analytical model of depth-dose distributions for carbon-ion beams. Available at: https://arxiv.org/html/2506.19479?utm_source=chatgpt.com. [Accessed: January 22 2026)
4. Kim, J., Park, M, JM., Wu, HC. Carbon Ion Therapy: A Review of an Advanced Technology. Progress in Medical Physics. 31(3): 71-80. Available at: https://www.progmedphys.org/journal/view.html?uid=870&&vmd=Full
5. Malouff et al (2020). Carbon Ion Therapy: A Modern Review of an Emerging Technology. https://www.frontiersin.org/articles/10.3389/fonc.2020.00082/full
6. Meschini, G., et al. (2022) Time-resolved MRI for off-line treatment robustness evaluation in carbon-ion radiotherapy of pancreatic cancer. Medical Physics. 49(4): 2386-2395. doi: 1002/mp.15510

Please Note: The Leo Cancer Care patient positioning system Eve has received FDA 510(k) clearance and is available for clinical use.