Carbon-ion cancer therapy, or carbon-ion radiotherapy (CIRT) is not a new concept but is showing new promise for the treatment of radiation resistant tumors and cancers like mesothelioma, certain types of carcinomas, and prostate cancer.
Radiation therapies use intense energy to destroy cancer cells. The result is reduction in number of cancerous cells or reduction in tumor size. Radiation therapies can be administered externally with high energy beams or internally by placing radioactive material in close proximity to the cancerous cells.
High energy particles are carefully directed to the tumor or cancer site and through a phenomenon called the Bragg curve, the particles lose their energy at the endpoint of their Bragg curve at the Bragg peak, which is where their action takes place. That endpoint tissue is cancerous and tissue in which the beam passes through is therefore less affected by those energy particles. This is the basic mechanism of carbon-ion therapy. Proton therapy is similar whereby charged particles are introduced to the cancerous tissue via an external beam. However, carbon ions are heavier and leave higher amounts of energy in the diseased tissue causing more destruction. Carbon-ion damage results in increased double-stranded DNA(dsDNA) breakage where proton therapy may not. Cellular repair mechanisms have a much harder time successfully correcting both strands.
CIRT is not an approved treatment option in the United States yet but there is mounting research indicating its benefits for patients with tumors resistant to conventional radiation therapy. There are current clinical trials taking place outside of the US utilizing CIRT for radiation resistant or inoperable high-risk tumors. One of the most active groups investigating the use of CIRT for patients in clinical trials is the University of Heidelberg in Germany. Additional countries in eastern Europe and Japan are currently conducting research for treatment of carcinomas, chordomas, glioblastoma, as well as pancreatic, prostate, rectal, and liver cancers.
The “magic” of CIRT is the potential maximization of cooperation between the body’s biology and the physics of the carbon atom interacting with that biological system. That unique Bragg curve allows less damage to surrounding tissues of the treatment site. The properties of the carbon ion including its potency and mechanism of complete breakage of dsDNA means fewer treatments for patients compared to traditional radiation therapies. In addition, researchers are looking at novel ways to combine therapies like CIRT plus chemotherapy or immunotherapy. The cooperation of the CIRT therapy with immunotherapy assists the body’s inherent abscopal effect for suppression of subsequent tumor development.
The United States does not have a CIRT capable facility; reportedly, the challenge is in the costs associated with this type of therapy. There are special requirements, including a particle accelerator, which put building estimates at $100+ million. Some consider CIRT so closely related to proton therapy which was historically fraught with cost issues, ethical testing concerns (present with many new technology treatments), and the learning required to interpret and fully utilize new technology for best practice and patient outcomes. The NIH has explored grant opportunities, one was called P20 to begin planning for a National Center for Particle Beam Radiation Therapy Research Center, and one grant was awarded to the North American Particle Therapy Alliance (NAPTA) which is a collaboration of US academic institutions, US National Laboratories, and the leading centers in Japan and Germany. More randomized clinical trials are needed to evaluate the efficacy and these collaborators are working together to make progress toward accessible CIRT in the US.
CIRT is not a fit for all types of cancers but for some, it has been shown to have reproducible outcomes on even the most refractory tumors.
Sources: NIH National Cancer Institute, NIH US Library of Medicine Clinical Trials, NIH Department of Health and Human Services, International Journal of Particle Theory, Cancer, Cancers (MDPI), Current Breast Cancer Reports,