Carbon ion therapy for retroperitoneal sarcoma is used by carbon ion cancer treatment centers in Japan and China for sarcomas behind the abdominal cavity that are hard to remove surgically or have grown back after surgery. Japan's QST Hospital analyzed 76 patients and reported a 5-year local control rate of 72.0% and 5-year overall survival of 49.4% (Cancers, 2025). In June 2026 the Shanghai Proton and Heavy Ion Center reported 5-year survival of 54.7% in 48 patients with unresectable soft tissue sarcoma (BMC Cancer). Carbon ion therapy for unresectable bone and soft tissue tumors is an approved, insurance-covered treatment in Japan; overseas patients receive it as self-pay care. To find out whether your scans qualify, request an eligibility and cost consultation.
Why do retroperitoneal sarcomas need options beyond surgery?
The retroperitoneum is the space behind the membrane lining the abdomen, where the kidneys, major blood vessels and spinal nerves run. Soft tissue sarcomas here (liposarcoma, leiomyosarcoma and others) cause few symptoms until they are large, and many exceed 10 cm at diagnosis. The standard treatment is surgery that removes the tumor with surrounding tissue.
When the tumor surrounds major vessels, or has recurred after several operations, further surgery becomes difficult. Conventional X-ray radiotherapy is limited by how much dose the nearby bowel can tolerate, so it is hard to deliver a dose strong enough to control a sarcoma.
Carbon ions release most of their energy at a set depth and then stop (the Bragg peak), sparing tissue behind the tumor. Their cell-killing effect is 2–3 times that of X-rays, which is why they have long been used for radioresistant sarcomas. See What Is Carbon Ion Therapy?
QST Hospital: 5-year results in 76 patients
QST Hospital in Chiba, Japan analyzed 76 patients with retroperitoneal sarcoma treated with carbon ions between April 2000 and March 2022 (Cancers, October 2025). Most (74 patients) received 70.4 Gy (RBE) in 16 fractions over 4 weeks.
| Outcome | 3 years | 5 years |
|---|---|---|
| Local control | 79.0% | 72.0% |
| Overall survival | 68.3% | 49.4% |
| Median survival | 58.1 months | |
| Acute grade 3 side effects | None | |
The authors concluded that carbon ion radiotherapy is a definitive treatment option for patients with unresectable retroperitoneal sarcoma, and called for multicenter studies to build on these results.
2026 results from the Shanghai center
The Shanghai Proton and Heavy Ion Center (SPHIC) published long-term results for 48 patients with unresectable primary or recurrent soft tissue sarcoma in BMC Cancer in June 2026. Forty were recurrent cases, and 75.0% of tumors were in the retroperitoneum or pelvis. Median follow-up was 48.6 months.
| Outcome | 4 years | 5 years |
|---|---|---|
| Local control | 65.8% | 60.3% |
| Overall survival | 59.7% | 54.7% |
| Median survival | 67.3 months | |
No patient had acute grade 2 or higher blood or digestive toxicity. Patients who received a biologically effective dose (BED) of 129 Gy or more had better local control, which may guide future dose planning.
In Germany, the Heidelberg Ion Beam Therapy Center is running a randomized phase II trial (Retro-Ion) comparing preoperative proton and carbon ion therapy. See carbon ion vs proton therapy.
Who is a candidate?
QST Hospital's English guide lists bone and soft tissue tumors that are difficult to remove surgically as indications. The final decision is made by Japanese physicians after reviewing imaging and pathology.
| Check | Favorable | Needs discussion first |
|---|---|---|
| Surgery | Hard to resect, or repeat surgery is a heavy burden | Clean resection judged possible |
| Location | Some distance from the bowel | Small or large bowel directly touching the tumor |
| Metastasis | None in other organs | Multiple sites such as lung or liver |
| Metal in field | None | Surgical clips or screws in the beam path |
| General condition | Independent daily living (PS 0–2) | Mostly bedbound |
When bowel is in contact with the tumor, a spacer operation to move it away may be considered first. For bone sarcomas see osteosarcoma carbon ion therapy and bone and soft tissue sarcoma.
Schedule and cost
Retroperitoneal sarcoma is usually treated in 16 fractions over 4 weeks. Planning CT/MRI and immobilization take 1–2 weeks, and QST notes about 1–2 weeks of free time before treatment starts. Plan for a 6–7 week stay. See treatment period.
| Institution | Fee for overseas patients | Basis |
|---|---|---|
| QST Hospital (Chiba) | 5.786 million yen (tax included) | Overseas patient page, updated 27 May 2026 |
| QST hospitalization, tests, visits | 33 yen per medical fee point (tax included) | Same page |
| Osaka Heavy Ion Therapy Center | 4.8 million yen + consumption tax | Center fee page |
These amounts exclude coordinator fees, flights and accommodation. Compare institutions in carbon ion therapy cost.
Before your consultation, prepare: CT/MRI from the last 3 months (DICOM), pathology report, previous surgery records (including clip or metal locations) and any radiotherapy history. With these, our team can move quickly. Phone +82-2-517-5117.
Side effects and how they are managed
In the QST series there were no acute grade 3 side effects. Mild skin redness, fatigue or digestive discomfort may occur during treatment and usually settle afterwards.
Late grade 3 or higher effects were reported in 4 of 76 patients (5.2%), including bowel injury, spinal fracture and reduced mobility, mostly when tumors were close to bowel or spine. Physicians therefore check the distance to the bowel carefully and adjust the dose distribution as needed, followed by regular CT/MRI. See side effects.
FAQ
My retroperitoneal liposarcoma has recurred. Can I receive carbon ion therapy?
In the Shanghai study, 40 of 48 patients had recurrent disease, and 5-year survival was 54.7%. If the recurrence is some distance from the bowel and there are no distant metastases, it can be considered. We start by reviewing your scans.
Can carbon ion therapy be given before surgery?
The Retro-Ion randomized phase II trial in Heidelberg compares preoperative protons and carbon ions. In Japan, treatment focuses on unresectable cases.
Do I need to be hospitalized?
Most patients are treated as outpatients. Admission may be recommended depending on condition, and is billed separately.
I had radiotherapy to the same area before.
Re-irradiation may be considered depending on the previous dose and timing. Please send your previous treatment records.
Related articles
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- Carbon Ion Radiotherapy for Retroperitoneal Sarcoma: A Single-Institution Study (QST Hospital). Cancers 2025;17(20):3395
- Li P, et al. Carbon ion radiotherapy for unresectable primary or recurrent soft tissue sarcomas: long-term outcomes. BMC Cancer 2026;26:959 (SPHIC)
- Retro-Ion: neoadjuvant irradiation of retroperitoneal soft tissue sarcoma with ions — randomized phase II pilot trial protocol (Heidelberg)
- QST Hospital — Information for patients from abroad (fees, updated 2026-05-27)
- QST Hospital — Bone and soft tissue tumors (indications for carbon ion radiotherapy)
- Osaka Heavy Ion Therapy Center — Treatment fees (Japanese)
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.