The difference between carbon ion and proton therapy comes down to the weight of the particle and how strongly it damages cancer cells. Carbon ion therapy uses carbon ions about 12 times heavier than protons, and QST Hospital in Japan explains that their cell-killing effect at the tumor is 2–3 times that of X-rays or protons. Both are established particle therapies in Japan: as of June 2024, public insurance covers both for eight conditions including prostate, liver, pancreatic and early lung cancer, while some cancers such as cervical adenocarcinoma are covered only for carbon ions and pediatric solid tumors only for protons. To find out which one may suit your diagnosis, send your records via our carbon ion and proton therapy consultation.
What is the difference between carbon ion and proton therapy?
X-rays leave dose along both the entry and exit paths through the body. Particle beams instead release most of their energy at a set depth and almost nothing beyond it (the Bragg peak), so dose can be concentrated on the tumor while sparing tissue behind it. Protons and carbon ions share this property. See What Is Carbon Ion Therapy? for an illustrated explanation.
The difference comes from mass. Carbon ions are about 12 times heavier than protons, scatter less sideways, and break DNA at several points at once inside the tumor. QST Hospital states in its guide for overseas patients that the cell-killing effect in the peak region is 2–3 times greater than X-rays or protons, which is why carbon ions are used for cancers that respond poorly to conventional radiation. Protons have a biological effect similar to X-rays, are offered at more centers, and are widely used for growing children.
| Item | Carbon ion therapy | Proton therapy |
|---|---|---|
| Particle | Carbon ion (about 12× a proton's mass) | Hydrogen nucleus (proton) |
| Cell damage at the tumor | 2–3× X-rays or protons (QST Hospital) | Similar to X-rays |
| Particular strengths | Radio-resistant cancers (sarcoma, adenocarcinoma), large tumors | Pediatric solid tumors, larger treatment areas |
| Centers in Japan | 7 (Chiba, Gunma, Kanagawa, Osaka, Hyogo, Saga, Yamagata) | More, across the country |
| Number of sessions | Relatively short (e.g., lung: 1 week, 4 sessions) | Relatively longer (e.g., lung: 2 weeks, 10 sessions) |
Which cancers use carbon ions and which use protons?
Hyogo Ion Beam Medical Center, which operates both beams, summarized Japan's public insurance coverage in its June 2024 newsletter as below. Insurance coverage marks where each therapy is recognized as standard care, so it is a useful guide to which beam is used for which cancer. Overseas patients do not use Japanese insurance, but hospitals often refer to this scope when judging eligibility.
| Insurance coverage (June 2024) | Carbon ion | Proton |
|---|---|---|
| Localized bone and soft tissue tumors (sarcoma) | Covered | Covered |
| Head and neck malignancies (excluding oral/pharyngolaryngeal squamous cell carcinoma) | Covered | Covered |
| Localized and locally advanced prostate cancer (non-metastatic) | Covered | Covered |
| Hepatocellular carcinoma ≥4 cm, intrahepatic cholangiocarcinoma | Covered | Covered |
| Locally advanced pancreatic cancer | Covered | Covered |
| Local recurrence of colorectal cancer after surgery | Covered | Covered |
| Early lung cancer (stage I–IIA, added June 2024) | Covered | Covered |
| Locally advanced cervical adenocarcinoma, cervical squamous cell carcinoma ≥6 cm, gynecologic melanoma | Covered | — |
| Pediatric solid malignant tumors (localized) | — | Covered |
Other conditions, such as locally advanced lung cancer, digestive and urological tumors including esophageal and kidney cancer, and metastatic tumors, continue to be treated under Advanced Medical Care. For hospital-specific eligibility criteria see Prostate cancer carbon ion therapy and Liver cancer carbon ion therapy criteria.
How do sessions and length of stay in Japan differ?
For patients traveling abroad, the most tangible difference is length of stay. Carbon ions can deliver a stronger dose per session, so the same cancer often needs fewer sessions. In the early lung cancer plans published by Hyogo Ion Beam Medical Center, carbon ion therapy took 1 week in 4 sessions and proton therapy 2 weeks in 10 sessions (or 6 weeks in 30). Below are the treatment periods each hospital publishes for overseas patients (carbon: QST Hospital; proton: University of Tsukuba Hospital Proton Beam Therapy Center).
| Cancer | Carbon ion (QST Hospital) | Proton (Tsukuba) |
|---|---|---|
| Prostate | 3 weeks | 4–5 weeks |
| Pancreas | 3 weeks | 5 weeks |
| Liver | 2 days–3 weeks | 2–7 weeks |
| Stage I lung | 1 day–3 weeks | 2–7 weeks |
| Head and neck | 4 weeks | 4–7 weeks |
The first visit, immobilization device, planning CT and waiting time come on top. QST Hospital notes a gap of about 1–2 weeks between preparation and the start of treatment, during which patients may go home as long as they return by the day before treatment. A shorter schedule reduces lodging, interpreting and family leave, so confirm the timeline at the consultation stage.
Which beam fits your schedule and budget depends on the stage and tumor location. If you have a diagnosis and imaging CD, please use our particle therapy consultation or call +82-2-517-5117.
How do outcomes and costs compare?
Good outcomes have been reported for both. In a study of 343 hepatocellular carcinoma patients treated at Hyogo Ion Beam Medical Center (242 proton, 101 carbon ion; Komatsu et al., Cancer 2011), 5-year local control was 90.8% overall and 93.0% in the carbon ion group. Rather than one beam always being better, it is more accurate to say that one may fit better depending on the tumor's nature, size and location. Recent liver results are covered in Liver cancer carbon ion therapy for tumors over 10 cm.
Published fees for overseas patients vary by hospital. For carbon ion therapy, QST Hospital lists 5.786 million yen (tax included; notice updated May 27, 2026) for patients without Japanese public insurance, with hospitalization and tests charged separately at 33 yen per fee point. The Tsukuba proton center does not publish a price for overseas patients and provides it through designated coordinators. When comparing carbon ion and proton costs, look at the total including lodging and interpreting for the length of stay, not only the technical fee. Domestic published prices are in Carbon ion therapy cost in Japan.
Steps to choose the right particle therapy
When looking into carbon ion and proton therapy in Japan together, organizing things in this order speeds up the consultation.
- Cancer type and stage: check where your cancer falls in the coverage table. Cervical adenocarcinoma points to carbon ions; pediatric solid tumors point to protons first.
- Previous radiation: if the same area has been treated, re-irradiation eligibility becomes central to the hospital's decision.
- Time available in Japan: if treatment must finish within 1–3 weeks, carbon ion therapy with fewer sessions may help.
- Referral route: both QST Hospital and Tsukuba accept overseas patients through registered medical coordinators. See 7 carbon ion therapy hospitals in Japan and Japanese Institutions.
- Documents: diagnosis letter, recent CT/MRI/PET imaging CD and reports, pathology report, surgery and chemotherapy records, medication list, passport copy.
The Tsukuba proton center lists good general condition, ability to travel to Japan and an expected prognosis of at least one year as conditions for overseas patients, and QST Hospital states it does not accept breast or esophageal cancer from overseas. Criteria differ by hospital, so a "no" from one center may still leave a path at another center or with the other beam.
Frequently asked questions
Is carbon ion therapy always better than proton therapy?
No. Carbon ions are strong for radio-resistant cancers and short schedules; protons are strong for children and larger treatment areas. For many cancers, such as hepatocellular carcinoma, high local control has been reported with both, and physicians choose according to the tumor.
How many sessions does carbon ion therapy take?
It depends on cancer type and stage, from as little as 1 day up to about 5 weeks. Per QST Hospital's overseas guide, prostate and pancreatic cancer take 3 weeks, and head and neck cancer and bone/soft tissue tumors 4 weeks.
Can I receive carbon ion therapy to an area already treated with protons?
The hospital decides individually based on prior dose, time elapsed and the state of nearby organs. Please prepare your previous radiation records (site and dose).
Can children receive carbon ion therapy?
Under Japanese insurance, pediatric solid malignant tumors are covered for proton therapy. Because sparing growing tissue matters, protons are often considered first for children.
Related articles
Wondering if carbon ion therapy is possible for you, and what it costs?
We help you prepare consultations with Japanese institutions and provide medical interpreting.
Free consultationCall +82-2-517-5117Sources
- QST Hospital — For patients from overseas (carbon ion radiotherapy)
- Hyogo Ion Beam Medical Center Newsletter No. 20, June 2024 — insurance coverage (Japanese document)
- University of Tsukuba Hospital Proton Beam Therapy Center — Conditions for Acceptance
- Komatsu S, et al. Clinical results and risk factors of proton and carbon ion therapy for hepatocellular carcinoma. Cancer 2011
- Current perspectives on radiotherapy in hepatocellular carcinoma management: a comprehensive review (PMC)
General information based on public sources; not a substitute for diagnosis or treatment. Eligibility is decided by the treating physicians. Written by the FTH editorial team.