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Summary To assess the achievement of uniformity of radiobiological effectiveness at different depths in the proton spread-out Bragg peak (SOBP), Chinese hamster ovary (CHO) cells were exposed to 65-MeV modulated proton beams at the Research Center for Nuclear Physics (RCNP) of Osaka University. We selected four different irradiation positions: 2 mm depth, corresponding to the entrance, and 10, 18 and 23 mm depths, corresponding to different positions in the SOBP. Cell survival curves were generated with the in vitro colony formation method and fitted to the linear-quadratic model. With 137CS gamma-rays as the reference irradiation, the relative biological effectiveness (RBE) values for a surviving fraction (SF) level of 0.1 are 1.05, 1.10, 1.12 and 1.19 for depths of 2, 10, 18 and 23 mm respectively. A significant difference was found between the survival curves at 10 and 23 mm (P < 0.05), but not between 18 and 10 mm or between 18 and 23 mm. There was a significant dependence of RBE on depths in modulated proton beams at the 0.1 surviving fraction level (P< 0.05). Moreover, the rise of RBEs significantly depended on increasing SF level or decreased approximately in correspondence with irradiation dose (P = 0.0001). To maintain uniformity of radiobiological effectiveness for the target volume, careful attention should be paid to the influence of depth of beam and irradiation dose.Keywords: proton; spread-out Bragg peak; relative biological effectiveness; Chinese hamster ovary cellThe depth-dose curve for the single-energy proton beam has limited applications in clinical radiation therapy owing to the excessively narrow high-dose region. This region, also known as the Bragg peak, can be modulated by appropriate selection of a distribution of proton energies to produce a spread-out Bragg peak (SOBP) or a uniform region of full dose at the depth of interest. Dose uniformity across a target volume can be achieved with multiple X-ray beams. However, each X-ray beam features a greater dose in the entrance region than a corresponding proton beam, has a dose gradient across the target volume and delivers an undesirable dose to normal tissues distal to the target. Proton beams have none of these undesirable characteristics (Suit and Urie, 1992; Munzenrider and Crowell, 1994;Raju, 1996).Although SOBP produces an excellent physical dose distribution, there is a variation of linear energy transfer (LET) values at different depths in the SOBP, known as the LET gradient, from proximal to distal SOBP. The proton is a lower LET particle than other heavy-charged particles; for example, the mean LET values of the 65-MeV modulated proton beams (SOBP) are always less than 7 keV .m-' (Courdi et al, 1994).The achievement of uniformity of radiobiological effectiveness for target volumes is always a matter of concern. In fact, there is no uniformity of LET within target volumes. One study has suggested that DNA double-strand breaks, potentially lethal damage and sublethal damage, depend on LET and are closely

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The monochromatic images acquired by Gemstone spectral imaging (GSI) mode on the GE CT750 HD theoretically determines the computed tomography (CT) number more accurately than that of conventional scanner. Using the former, the CT number is calculated from (synthesized) monoenergetic X‐ray data. We reasoned that the monochromatic image might be applied to radiotherapy treatment planning (RTP) to calculate dose distribution more accurately. Our goal here was to provide CT to electron density (ED) conversion curves with monochromatic images for RTP. Therefore, we assessed the reproducibility of CT numbers, an important factor on quality assurance, over short and long time periods for different substances at varying energy. CT number difference between measured and theoretical value was investigated. The scanner provided sufficient reproducibility of CT numbers for dose calculation over short and long time periods. The CT numbers of monochromatic images produced by this scanner had reasonable values for dose calculation. The CT to ED conversion curve becomes linear with respect to the relationship between CT numbers and EDs as the energy increases. We conclude that monochromatic imaging from a fast switching system can be applied for the dose calculation, keeping Hounsfield units (HU) stability.PACS numbers: 87.55.‐x, 87.55.ne, 87.57.N‐, 87.59.bd

The linker of nucleoskeleton and cytoskeleton (LINC) complex is a multifunctional protein complex that is involved in various processes at the nuclear envelope, including nuclear migration, mechanotransduction, chromatin tethering and DNA damage response. We recently showed that a nuclear envelope protein, Sad1 and UNC84 domain protein 1 (SUN1), a component of the LINC complex, has a critical function in cell migration. Although ionizing radiation activates cell migration and invasion in vivo and in vitro, the underlying molecular mechanism remains unknown. Here, we examined the involvement of the LINC complex in radiation‐enhanced cell migration and invasion. A sublethal dose of X‐ray radiation promoted human breast cancer MDA‐MB‐231 cell migration and invasion, whereas carbon ion beam radiation suppressed these processes in a dose‐dependent manner. Depletion of SUN1 and SUN2 significantly suppressed X‐ray‐enhanced cell migration and invasion. Moreover, depletion or overexpression of each SUN1 splicing variant revealed that SUN1_888 containing 888 amino acids of SUN1 but not SUN1_916 was required for X‐ray‐enhanced migration and invasion. In addition, the results suggested that X‐ray irradiation affected the expression level of SUN1 splicing variants and a SUN protein binding partner, nesprins. Taken together, our findings supported that the LINC complex contributed to photon‐enhanced cell migration and invasion.