The rotating gantry, a key part of the modern carbon ion therapy machine, is delivering strong results in real patients. In a prospective study at QST Hospital (Chiba, Japan) published in the Journal of Radiation Research in 2025, 21 patients with choroidal malignant melanoma of the eye were treated with a superconducting rotating gantry and scanning beams. Three-year local control, overall survival and eye retention were all 100%. This article explains how carbon ion machines have evolved, the study results, who is eligible, the 4-day schedule and the published cost for overseas patients (5.786 million yen at QST Hospital). To ask whether this is an option for you, use our eye melanoma carbon ion therapy consultation.
What does a carbon ion therapy machine look like?
A carbon ion therapy system has three main parts: an ion source and linear accelerator that create carbon ions and give them their first push; a ring-shaped synchrotron that accelerates them to the speed needed to reach deep tumors; and beam transport and delivery equipment that carries the beam to the treatment room and aims it at the patient. The whole system fills a dedicated building.
Carbon ions release most of their energy at a set depth and then stop (the Bragg peak), so the tumor receives a high dose while tissue behind it receives little. See What Is Carbon Ion Therapy? for the basics and our carbon ion vs proton therapy comparison.
Early machines delivered beams only from fixed directions (vertical or horizontal), so patients sometimes had to tilt their body to reach the right angle. The rotating gantry was developed to remove this limit.
What does a rotating gantry change?
A rotating gantry turns the huge beam-bending magnet structure 360 degrees around the patient, sending the beam from any direction while the patient lies comfortably. Carbon ions are much heavier than protons and harder to bend, so carbon gantries were long seen as too large and heavy. Steady engineering progress has made them smaller, and several Japanese carbon ion cancer treatment centers now use them for patient care.
| Facility | Gantry feature | Published size / weight | Source |
|---|---|---|---|
| HIT, Heidelberg, Germany | World's first 360° carbon ion gantry (conventional magnets) | 25 m long, 13 m diameter, about 670 t | Helmholtz Association |
| QST Hospital, Chiba, Japan | Superconducting rotating gantry, treatment since May 2017 | About 14 m long, 6.5 m end-ring diameter, about 300 t | IPAC 2018 paper |
| Yamagata University, East Japan Heavy Ion Center | Second-generation compact superconducting gantry | About 10 m long, about 200 t | nippon.com |
Superconducting magnets create much stronger fields in the same space, so the QST gantry weighs less than half of the German design. Scanning beams add precision: a beam a few millimetres wide "paints" the tumor point by point, matching its shape. Patients can stay in a comfortable position, and doctors can more easily choose angles that avoid the eye, brain or spinal cord.
Latest results for choroidal melanoma
Choroidal melanoma is a malignant tumor in the choroid, a layer inside the eye. The goal is to control the tumor while keeping the eye and vision, so precise angle selection matters. QST Hospital has treated this disease with carbon ions since 2001, with more than 200 patients by 2017 (hospital data). This prospective study checked that results remained excellent after switching to the new gantry and scanning beams.
Twenty-one patients (median age 62) were enrolled from April 2018 to July 2019. Median tumor diameter was 11.0 mm and height 5.5 mm; in 6 patients the tumor touched the optic disc. All received 68 Gy (RBE) in 4 fractions over 4 days from two beam directions. All 21 completed treatment and were followed for a median of 43 months.
| Item | Result | Note |
|---|---|---|
| 3-year local control | 100% | No recurrence at the treated site |
| 3-year overall survival | 100% | All 21 patients alive |
| 3-year eye retention | 100% | No enucleation |
| Vision kept | 13 of 17 (76.5%) | Among patients with 20/200 or better before treatment |
| Acute side effects | No grade 2 or higher | Skin and eye reactions grade 0–1 |
| Neovascular glaucoma | Grade 2 in 3 patients | No grade 3 or higher |
The authors concluded that effectiveness and safety were equivalent to the conventional fixed-beam method. A 2025 long-term report from the same team (IJROBP) also showed 94.4% five-year local control in 250 patients, in line with these results. Three patients later developed liver metastases and went on to receive liver resection or immunotherapy, so regular liver imaging is recommended after treatment.
Eligibility and schedule
According to QST Hospital, the indication is choroidal melanoma confined to the orbit with no distant metastasis, currently treated within a clinical study. See our eye tumor carbon ion therapy page for full criteria.
- Fractions: 4 treatments over 4 days in this study
- Preparation: examination, CT/MRI, planning and immobilization, usually 1–2 weeks
- During treatment: practice keeping the eye fixed in one direction
- After treatment: regular eye exams and liver imaging
The short schedule makes it easier for overseas patients. Compare Japanese centers on our Japanese institutions page.
Carbon ion therapy cost for overseas patients
Amounts published on QST Hospital's English page for overseas patients (checked October 20, 2026), for patients not covered by Japanese public insurance:
| Item | Amount | Note |
|---|---|---|
| Carbon ion radiotherapy | 5.786 million yen (tax incl.) | QST Hospital published price |
| Hospital stay, visits, tests | 33 yen per medical fee point | Charged separately |
| Coordinator fee | Not included | Registered coordinator or travel agency required |
| Stay, flights, interpreting | Not included | Depends on your plans |
Prices differ by hospital; see carbon ion therapy cost in Japan. The final total depends on tests and length of stay and is confirmed after the hospital reviews your records.
We can give a more precise answer after reviewing your records. Contact us for a free consultation or call +82-2-517-5117.
Document checklist before consultation
- Ophthalmology report (tumor location, diameter and height)
- Fundus photos, ocular ultrasound, fluorescein angiography
- Eye/orbit MRI and whole-body CT or PET-CT (original images on CD) with reports
- Recent blood tests including liver function
- Visual acuity and eye pressure records, previous treatments
- Passport copy and preferred treatment timing
At QST Hospital, a physician reviews your data first and makes the final eligibility decision. Complete records speed up the reply.
FAQ
How is a rotating gantry different from standard carbon ion therapy?
The beam direction can change through 360 degrees while you lie comfortably. In the 2025 QST study, 21 choroidal melanoma patients had 100% three-year local control, survival and eye retention.
Is vision preserved after carbon ion therapy for eye melanoma?
In this study, 13 of 17 patients (76.5%) who had 20/200 or better kept that level. It depends on how close the tumor is to the optic nerve and macula.
How long does treatment take?
Irradiation itself takes 4 sessions over 4 days. Planning adds 1–2 weeks, so a stay in Japan of roughly 2–3 weeks is typical, adjusted to the hospital schedule.
What side effects can occur?
Acute side effects were mild, with none at grade 2 or higher. Neovascular glaucoma can develop over the following years (grade 2 in 3 patients here) and is managed through regular eye checks.
How much does it cost for overseas patients?
QST Hospital publishes 5.786 million yen (tax included) for carbon ion radiotherapy, with hospital stay and tests at 33 yen per point. Coordinator fees and living costs are extra.
Related articles
Wondering if carbon ion therapy is possible for you, and what it costs?
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Free consultationCall +82-2-517-5117Sources
- Wakatsuki M, et al. Prospective study of a rotating gantry with scanning beams of carbon-ion radiotherapy for choroidal malignant melanoma. J Radiat Res 2025;66(4):408-414
- Aoki S, et al. Long-Term Outcomes of Ocular and Visual Preservation After Carbon Ion Radiation Therapy for Choroidal Malignant Melanoma. IJROBP 2025;121(4):991-999
- QST Hospital — Indications: Eye tumors (choroidal malignant melanoma)
- QST Hospital — For patients from abroad (costs, procedure)
- IPAC2018 — Superconducting rotating gantry for carbon-ion radiotherapy (HIMAC/QST)
- Helmholtz Association — The largest weapon to combat cancer (HIT gantry)
- nippon.com — Yamagata University's East Japan Heavy Ion Center
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.