Abstract
Introduction: Carbon-ion radiotherapy (C-ion RT) is known as a highly effective local treatment and its relative biological effectiveness (RBE) has been evaluated for various types of malignant tumors. There are only a few studies on C-ion radio sensitivity in breast cancer, and there has been no evaluation by subtypes. To estimate the impact of C-ion RT for breast cancer, RBE of C-ion beams of various types of human breast cancer cell lines was evaluated by comparison with X-rays. Methods: Six human breast cancer cell lines with different subtypes, Luminal-human epidermal growth factor receptor 2 (HER2)-negative (MCF-7), Luminal-HER2-positive (BT-474), Her2-enriched (SK-BR-3), Basal-like (MDAMB- 468, HCC1937) and ductal carcinoma in situ (MCF10DCIS.com) were used. Radio sensitivities were assessed with survival curves created from colony-forming assay (CFA) and high-density surviving assay (HDS). An X-ray generator was used with 200 kV, 20 mA. The Heavy Ion Medical Accelerator in Chiba (HIMAC) was used for C-ion irradiation, with 290 MeV/u, mono-peak, linear energy transfer (LET) of 80 KeV/μm. Results: CFA was not suitable for BT474, SK-BR-3, MDA-MB-468, and HCC1937 because of their low plating efficiency. The differences between the D10 values on HDS were large with X-ray, and the survival curve shoulders for MCF7, MDA-MB-468, and MCF10DCIS.com were wide. On the other hand, the differences between the D10 values were small with C-ion beams, and the survival curves were linear without shoulders for all cell lines except a small shoulder with MCF10DCIS.com. The RBE value of C-ion beams was 2.3 to 3.6, median 2.9 in all cell lines by CFA and HDS. Conclusion: RBE around 3 by C-ion beams was seen in many types of ductal cancer. The small survival curve shoulder on MCF10DCIS.com suggested that non invasive ductal carcinoma is relatively more resistant than invasive cancer.
Highlights
Carbon-ion radiotherapy (C-ion RT) is known as a highly effective local treatment and its relative biological effectiveness (RBE) has been evaluated for various types of malignant tumors
We had searched for other assays that could evaluate radio sensitivity in a manner similar to the usual culture, and we found articles on high-density surviving assay (HDS), reportedly effective for evaluating the radiosensitivity of cell lines with low Plating efficiency (PE) [11,12]
Carbon-ion beams were effective against any type of breast cancer cell lines
Summary
Carbon-ion radiotherapy (C-ion RT) is known as a highly effective local treatment and its relative biological effectiveness (RBE) has been evaluated for various types of malignant tumors. To estimate the impact of C-ion RT for breast cancer, RBE of C-ion beams of various types of human breast cancer cell lines was evaluated by comparison with X-rays. Radiotherapy with X-rays plays an important role in the treatment of breast cancer for breast irradiation of breast-conserving therapy, post-mastectomy regional radiotherapy, and recurrent tumor radiotherapy. The treatment effects are limited, as the local control rate is attenuated by post-operative micro residual tumor cells. Carbon-ion radiotherapy (C-ion RT), one of the types of heavy particle radiotherapy, with high biological effect and good dose distribution, has been reported to be effective for locally advanced tumor and radio resistant tumor [1].
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