Carbon-Ion Radiotherapy 'Very Effective' in Unresectable CRC

M. Alexander Otto, PA, MMS

December 22, 2022

The study covered in this summary was published on as a preprint and has not yet been peer reviewed.

Key Takeaway

  • Carbon-ion radiotherapy is a promising treatment for unresectable, locally recurrent colorectal cancer (CRC), including for patients who have undergone radiotherapy before.

Why This Matters

  • Carbon-ion radiotherapy is more potent and more focused than conventional radiotherapy but is typically not offered in the United States.

  • The long-term prognosis for patients with unresectable, locally recurrent CRC with conventional chemotherapy or chemoradiotherapy is poor; previous studies have reported 3-year overall survival of 4% to 24% for patients who undergo chemoradiotherapy or x-ray therapy.

  • From the current findings, investigators concluded that carbon-ion radiotherapy for locally recurrent CRC "is a very effective and promising treatment" alternative and is "potentially curative."

  • Carbon-ion radiotherapy is covered by national health insurance in Japan and is expected to be introduced in various countries, including the United States, soon.

Study Design

  • The team reviewed carbon-ion radiotherapy outcomes for 473 patients with unresectable, locally recurrent CRC who underwent treatment from 2003–2019, including 83 who had previously undergone x-ray or proton-beam radiotherapy.

  • Carbon-ion radiotherapy was administered 4 days per week for 16 fractions.

  • The total dose was 73.6 Gy for radiotherapy-naive patients and 70.4 Gy for patients who had previously undergone radiotherapy.

  • Concurrent chemotherapy was not used.

  • Exclusion criteria included recurrence at the anastomotic site and invasion of the intestines or bladder.

  • Surgical procedures, including placement of spacers and diversion colostomies, were used in some cases to reduce the risk of intestinal damage.

  • The median follow-up was 4 years.

Key Results

  • Three-year overall survival was 73% for radiotherapy-naive patients and 76% for patients who had previously undergone radiotherapy; for both groups, 3-year local control was achieved for 80% of patients.

  • Five-year overall survival was 50% in both groups; 5-year local control was achieved in 72% of the radiotherapy-naive group and in 69% of patients who had previosly undergone radiotherapy.

  • A history of resection of distant metastases did not affect prognosis.

  • The rate of adverse events of grade 3 or higher was greater among the patients who had previously undergone radiotherapy than among the radiotherapy-naive group. Early toxicities occurred in 7.2% of the patients who had previosly undergone radiotherapy; late events occurred in 26.5% of these patients. Among radiotherapy-naive patients, the rates were 1% and 5.9%, respectively.

  • But adverse event rates among the patients who had previously undergone radiotherapy were the same as observed with x-ray treatment and surgical resection.


  • It was a single-center, retrospective study.

  • Locally recurrent CRC diagnosis was not always confirmed by pathology.

  • Long-term results were not achieved by carbon-ion radiotherapy alone but by the best possible treatment for the patient, which could have included chemotherapy after treatment.


  • No external funding was reported, and the investigators did not disclose relevant financial relationships.

This is a summary of a preprint research study, "Carbon-Ion Radiotherapy for Unresectable Locally Recurrent Colorectal Cancer: A Promising Curative Treatment for Both Radiotherapy-Naive Cases and Re–Irradiation Cases," led by Hirotoshi Takiyama of QST Hospital in Chiba, Japan, provided to you by Medscape. The study has not been peer reviewed. The full text can be found at

M. Alexander Otto is a physician assistant with a master's degree in medical science and a journalism degree from Newhouse. He is an award-winning medical journalist who has worked for several major news outlets before joining Medscape and also an MIT Knight Science Journalism fellow. Email:

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