Carbon ion therapy for recurrent rectal cancer treats rectal cancer that has come back inside the pelvis after surgery, without another open operation, and it is one of the most experienced fields of carbon ion therapy in Japan. Japan has covered carbon ion therapy for postoperative colorectal cancer recurrence under public insurance since April 2022, and in 2025 a new study reported a 3-year survival rate of 90% in 12 patients with recurrent rectal cancer judged "unresectable", who received carbon ion therapy followed by laparoscopic bowel resection. This article summarizes the latest results, eligibility, the 4-week schedule and costs for overseas patients. To check first whether treatment is possible with your own scans and surgical records, send them through our recurrent rectal cancer carbon ion therapy consultation.
Why consider carbon ion therapy for recurrent rectal cancer?
Even after successful surgery, rectal cancer can grow back inside the pelvis, especially in front of the sacrum or along the pelvic side wall. Such local recurrences sit close to the original surgical site and to nerves, vessels and bone, so a second operation is often difficult. Patients who already received X-ray radiotherapy to the pelvis may also be unable to receive a sufficient dose again with conventional radiation.
Carbon ions release most of their energy at a set depth and then stop (the Bragg peak), and their cell-killing power is greater than that of X-rays. This allows a high dose to be concentrated on recurrent tumors that respond poorly to conventional radiation. See What Is Carbon Ion Therapy? for the basics. Since April 2022, carbon ion therapy for postoperative colorectal cancer recurrence has been covered by Japan's public insurance; the newsletter of the Japanese Society for Radiation Oncology (JASTRO) lists it among five covered indications, together with hepatocellular carcinoma and pancreatic cancer.
New 2025 result: bowel resection after carbon ion therapy, 90% 3-year survival
The main challenge in carbon ion therapy is bowel (small intestine or the anastomosis) lying right next to the tumor. Bowel is sensitive to radiation, so when it touches the tumor, patients have needed a "spacer" operation first, or treatment was not possible. Surgeons at Hyogo Medical University and QST Hospital reversed the order: carbon ion therapy first, then laparoscopic removal of the high-dose bowel segment about 4 weeks later.
| Item | Details (Cancers 2025;17(13):2230) |
|---|---|
| Patients | 12 patients with locally recurrent rectal cancer judged unresectable (2019–2023) |
| Carbon ion dose | 73.6 Gy (RBE) in 16 fractions for 9 patients; 70.4 Gy (RBE) in 16 fractions for 3 patients with prior pelvic radiotherapy |
| Timing of bowel resection | Median 4 weeks (3–8) after carbon ion therapy; all 12 laparoscopic |
| 3-year overall survival | 90% (median follow-up 40 months) |
| 3-year in-field recurrence-free survival | 90% |
| 3-year out-of-field recurrence-free survival | 72.2% |
There were no severe acute side effects during treatment. Late effects were sciatic nerve pain in 3 patients (grade 1 in 2, grade 3 in 1); the grade 3 patient could walk with assistance. After surgery, 1 patient had pancreatitis (Clavien–Dindo IIIa) and 4 had grade II complications such as anastomotic bleeding, urinary dysfunction or ileus, all managed with treatment. The authors concluded that this strategy may provide favorable outcomes for patients with unresectable recurrent rectal cancer. With 12 patients, results in larger groups are expected to follow.
The Gunma prospective study and QST Hospital's 577 patients
This new approach builds on long-standing results from Japanese carbon ion centers. Gunma University Heavy Ion Medical Center ran a prospective study (GUNMA 0801), and QST Hospital (Chiba) treated 577 patients with pelvic recurrence between 1994 and 2018.
| Source | Patients | Key results |
|---|---|---|
| GUNMA 0801, Frontiers in Oncology 2019 | 28 patients with postoperative pelvic recurrence of rectal cancer (no prior radiation to the area); 73.6 Gy (RBE) in 16 fractions over 4 weeks | 3-year local control 86%, 3-year survival 92% |
| QST Hospital overseas patient page (citing Yamada et al. 2016) | Pelvic recurrence after rectal cancer surgery | 5-year local control 88%, 5-year survival 59% |
In the Gunma study there were no grade 3 or higher acute side effects; late pelvic infection occurred in 2 patients (7%). The authors described carbon ion therapy as "a highly curative and less invasive local treatment". See also our summary Carbon ion therapy for colorectal cancer recurrence after surgery.
Who is eligible?
QST Hospital's published English criteria for postoperative colorectal cancer recurrence are summarized below. The final decision is made by the treating physician after reviewing scans and records.
| Check | Likely eligible | Discuss first |
|---|---|---|
| Site of recurrence | Recurrence inside the pelvis after colorectal surgery | Multiple recurrences outside the pelvis |
| Metastasis | No distant metastasis | Lung or liver metastases at the same time |
| Distance to bowel/bladder | Adequate distance between tumor and bowel/bladder | Bowel in contact (spacer surgery or the 2025 approach above may be considered) |
| Infection | No infection inside the pelvis | Fistula or abscess |
| Prior radiation | Prior pelvic radiotherapy does not rule out treatment | Submit dose records |
Even if you were told that bowel contact makes carbon ion therapy difficult, Japanese hospitals may review options with surgeons, such as changing the order of surgery or placing a spacer. Compare centers and contact routes in Japanese Institutions and 7 carbon ion therapy hospitals in Japan.
Schedule and cost
Most of the studies above used 16 fractions over about 4 weeks (once a day on weekdays). According to QST Hospital, once eligibility is confirmed from your records, you have a first visit and preparation tests; during the 1–2 weeks of treatment planning you may return home if you are back by the day before treatment starts.
| Item | QST Hospital (Chiba), overseas patients |
|---|---|
| Carbon ion therapy fee | 5,786,000 yen (tax included, self-pay) |
| Hospitalization, consultations, tests | 33 yen per medical fee point (tax included) |
| Separate | Medical coordinator fee, flights, accommodation, interpreting, and the cost of bowel surgery if performed |
Amounts are from QST Hospital's overseas patient page (accessed 22 October 2026) and may change with hospital revisions and exchange rates. Japanese public insurance applies only to people enrolled in it. See carbon ion therapy cost comparison for totals including stay.
For a recurrent rectal cancer consultation, prepare ① the original operation record and pathology ② CT, MRI or PET-CT images from the last 3 months (CD) ③ prior radiotherapy dose records ④ chemotherapy history. Send them and we will check eligibility for carbon ion therapy in Japan and the expected cost.
FAQ
I have already had pelvic radiotherapy. Is carbon ion therapy still possible?
Possibly. QST Hospital states that prior pelvic radiotherapy does not rule out treatment, and in the 2025 study 3 previously irradiated patients were treated with an adjusted dose (70.4 Gy (RBE) in 16 fractions). Be sure to bring your prior dose records.
I was told the recurrent tumor touches the bowel. Are there options?
Yes. A spacer operation can move the bowel away first, or, as in the 2025 Hyogo Medical University–QST Hospital study, the high-dose bowel can be removed laparoscopically about 4 weeks after carbon ion therapy. Japanese surgeons and radiation oncologists decide which fits after reviewing the images.
How many sessions and how long does it take?
In both the studies and hospital guidance, usually 16 fractions over about 4 weeks, plus the first visit, preparation tests and treatment planning (about 1–2 weeks, during which you may return home).
How much does carbon ion therapy cost?
For overseas patients at QST Hospital, the carbon ion therapy fee is 5,786,000 yen (tax included); hospitalization and tests are charged separately at 33 yen per medical fee point (accessed 22 October 2026).
What side effects can occur?
Severe acute side effects were rare in the studies; late nerve pain or pelvic infection was reported in some patients. Hospitals reduce the dose to nerves and bowel at the planning stage and follow patients regularly after they return home. See carbon ion therapy side effects.
Related articles
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- Hyogo Medical University · QST Hospital, Cancers 2025;17(13):2230 — Upfront carbon-ion radiotherapy followed by surgical resection of the irradiated intestines
- Gunma University, Frontiers in Oncology 2019 — GUNMA 0801 prospective study of carbon-ion radiotherapy for pelvic recurrence of rectal cancer
- QST Hospital — Colorectal cancer postoperative recurrence (indications, English)
- QST Hospital — Treatment for overseas patients (costs)
- JASTRO Newsletter 144 — 2022 insurance coverage of particle therapy
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.