Heavy ions are the radiation that is obtained by accelerating charged nuclei heavier than protons. Heavy ions produce ionization along their way, cause irreparable clustered DNA damage, and alter cellular ultrastructure. Radiotherapy success is limited by the toxicity in the normal tissue. X-rays are delivered from an external source, and they deposit most of their energy upstream of the tumor in healthy tissue. The deposition of energy also occurs beyond the tumor, which also affects the additional healthy tissue.
In conventional X-ray radiotherapy, the radiation dose decreases because the depth of penetration within the body increases. In heavy-ion radiotherapy, however, the radiation dose increases with depth to supply a peak (called a Bragg peak) during a finite depth of the body, enabling selective irradiation of cancers.
In heavy-ion radiotherapy, a sufficient dose often targets the lesion, with the height conforming to its shape and position (depth). To deliver ion beams precisely to any irregular lesion shape, individually specialized instruments called a collimator and a compensating filter are used.
Heavy ion irradiation is individualized, making it possible to attenuate the unnecessary dose to the critical organs such as the medulla spinalis, brain stem, and intestines.
The most serious impediment to developing heavy-ion therapy centers in the United States has been the high initial capital cost. The cost of a state-of-the-art heavy-ion system with the capacity to treat 1000 cancer patients per year, while approximately twice as expensive as a similarly sized proton center, remains less than that of the development of a biological agent and chemotherapeutic. The high cost of a heavy-ion therapy system compared with conventional X-rays is because of the complexity of the procedure required to reach deeply seated tumors. An instantaneous got to construct a heavy-particle therapy and research center using existing, proven, and reliable technology to treat patients and conduct research.
Also Read: Proton Therapy
Heavy ions, such as carbon, have gained remarkable interest because of their advantageous physical and radiobiologic properties compared to photon-based therapy. Among different kinds of ion beams, carbon ion beams, in particular, are used for cancer therapy because they are considered to have the most balanced, ideal properties due to their intensive killing effects on cancers and the potential ability of selective irradiation. An ideal heavy-ion should have lower toxicity in the initial tissues (normal tissue) and be more effective in the target region (tumor). Carbon ions are chosen as they represent the most straightforward combination in this direction.
In the target region, they need increased relative biological effectiveness and a reduced oxygen enhancement ratio compared to X-rays.
Carbon ion radiotherapy has been studied for every type of cancer, including intracranial malignancies, head and neck cancer, primary and metastatic lung cancers, gastrointestinal cancer, prostate cancer, genitourinary cancers, breast cancer, gynecologic cancer malignancies, and pediatric cancers.
Carbon exhibits a higher LET ( linear energy transfer) than protons and photons, leading to a higher RBE (relative biological effectiveness), where the damage caused by carbon ions is clustered within the DNA, overwhelming the cellular repair systems.
The idea that metastatic disease may be cured, with combination immunotherapy-radiation therapy (CIR) forms a potential therapy regimen. Both experimental and clinical evidence suggest that particle therapy, exceptionally high linear energy transfer (LET) carbon-ion therapy, demonstrates improvement in metastasis rate and a reduction in local recurrence. Combined carbon-ion therapy with immunotherapy demonstrates increased antitumor immunity and a reduced number of metastases compared with immunotherapy alone
New radiotherapeutic techniques minimize exposure to normal tissues to reduce acute and late adverse effects of treatment. Radiation therapy is commonly administered following mastectomy in many locally advanced cancers and is still being elicited.
Reduction in the risk of secondary malignancy is an important goal of radiation oncologists, as many patients treated for breast cancer have decades-long life expectancies. Previous studies have suggested an approximately 3.4% risk of radiation-induced secondary malignancies following radiotherapy.
Carbon ion therapy demonstrates a better dose distribution compared to proton therapy in most cases of early-stage lung cancer. carbon ion therapy was found safer for treating patients with adverse conditions such as large tumors, central tumors, and poor pulmonary function. Surgical resection with lobectomy has been the standard treatment choice for early-stage NSCLC (non-small-cell lung cancer). Radiotherapy is an option for patients who are not suitable for surgery or refuse it.
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Jin Y, Li J, Li J, Zhang N, Guo K, Zhang Q, Wang X, Yang K. Visualized Analysis of Heavy Ion Radiotherapy: Development, Barriers and Future Directions. Front Oncol. 2021 Jul 9;11:634913. doi: 10.3389/fonc.2021.634913. PMID: 34307120; PMCID: PMC8300564.
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