Phase I/II clinical trials of carbon ion therapy for prostate cancer

Heavy ion beams possess high linear energy transfer components and a prominent Bragg peak in the human body, resulting in higher relative biological effectiveness and improved dose distribution. To establish heavy ion therapy techniques for the treatment of prostate cancer, phase I/II clinical trials were initiated.

For 96 patients with T1b-T3 prostate cancer, three carbon ion beams were used to irradiate the prostate and seminal vesicles (20 times/5 weeks) with or without endocrine therapy. Radiation dose was expressed in GyE which was initially thought to be equivalent to photon dose. Total dose was gradually increased from 54 to 72 GyE.

Carbon ion therapy was completed in 20 cases of T1b/T1c/T2aN0M0 as monotherapy, in 8 cases of T2b/T3pN0M0 with neoadjuvant endocrine therapy, and in 68 cases of T2b/T3N0/pN1M0 with neoadjuvant and adjuvant endocrine therapy. Median observation period was 47 months. Grade 3 late radiation morbidity of rectum and/or bladder/urethra developed in one and five cases who received 66 and 72 GyE of radiation, respectively. After these adverse effects were observed, total dose was decreased to 66 GyE and the radiation field was coned down during the treatment course. At 5 years, overall, cause-specific, clinical recurrence-free, and biochemical recurrence-free survival rates were 87.7, 94.9, 90.0, and 82.6%, respectively. Local control was achieved in all patients except one patient who received 54 GyE of radiation.

The therapeutic techniques of carbon ion therapy have been established for patients with prostate cancer. Carbon ion therapy may exert excellent effect to the tissues of prostate cancer.