Carbon-Ion Beam Radiosensitivity Study and Biological Responses of High-Yielding Rice Line, MR219-PL-5

The carbon ion-beam has emerged as a novel physical mutagen for creating genetic variability and crop improvement. In this study, seeds of a high-yielding pyramided rice line MR219-PL-5 were exposed to carbon ion beam irradiation at 10, 20, 40, 60, 80, and 100 Gy. The radiosensitivity test was conducted to determine the optimum dose of carbon ion beam irradiation based on the lethal dose 50% (LD50) using Sandwich Blotter Technique. The biological responses of carbon-ion beam irradiation were also observed in other characteristics such as germination rate (GeR), survival rate (SR), growth rate (GRoR), shoot length (SL), root length (RL), seedling height (SH), days to flowering (DTF), fertility rate (FR) and thousand-grains weight (TGW). Based on the polynomial curve of SR graph, the lethal dose 50% (LD50) value was 86.12 Gy. However, the optimum dose range of carbon ion-beam irradiation was between 40 and 60 Gy as these two doses recorded the highest SR, 63 and 67%, respectively. Furthermore, the shoulder dose in this study was 60 Gy since SR decreased significantly at higher doses. M1 individuals irradiated at 40 and 60 Gy had the best biological responses where significant differences were found for SR, SL, RL, GRoR, SH, DTF and FR at these two doses compared to the other doses. Further studies on M2 and M3 populations could help to identify potential individuals as well as to understand the inheritance of each trait of interest from one generation to the next.

Experimental determination of modulation power of lung tissue for particle therapy

In particle therapy of lung tumors, modulating effects on the particle beam may occur due to the microscopic structure of the lung tissue. These effects are caused by the heterogeneous nature of the lung tissue and cannot be completely taken into account during treatment planning, because these micro structures are too small to be fully resolved in the planning CT. In several publications, a new material parameter called modulation power (P mod ) was introduced to characterize the effect. For various artificial lung surrogates, this parameter was measured and published by other groups and ranges up to approximately 1000 µm. Studies investigating the influence of the modulation power on the dose distribution during irradiation are using this parameter in the rang of 100 to 800 µm. More precise measurements for P mod on real lung tissue have not yet been published. In this work, the modulation power of real lung tissue was measured using porcine lungs in order to produce more reliable data of P mod for real lung tissue. For this purpose, ex-vivo porcine lungs were frozen in a ventilated state and measurements in a carbon ion beam were performed. Due to the way the lungs were prepared and transferred to a solid state, the lung structures that modulate the beam could also be examined in detail using micro CT imaging. An optimization of the established methods of measuring the modulation power, which takes better account of the typical structures within lung tissue, was developed as well.

Stopping-power ratio of mouthpiece materials for charged-particle therapy in head and neck cancer

In this study, the stopping-power ratios (SPRs) of mouthpiece materials were measured and the errors in the predicted SPRs based on conversion table values were further investigated. The SPRs of the five mouthpiece materials were predicted from their computed tomography (CT) numbers using a calibrated conversion table. Independently, the SPRs of the materials were measured from the Bragg peak shift of a carbon-ion beam passing through the materials. The errors in the SPRs of the materials were determined as the difference between the predicted and measured values. The measured SPRs (errors) of the Nipoflex 710™ and Bioplast™ ethylene–vinyl acetate copolymers (EVAs) were 0.997 (0.023) and 0.982 (0.007), respectively. The SPRs of the vinyl silicon impression material, light-curable resin, and bis-acrylic resin were 1.517 (0.134), 1.161 (0.068), and 1.26 (0.101), respectively. Among the five tested materials, the EVAs had the lowest SPR errors, indicating the highest human-tissue equivalency.

Genome and transcriptome-based characterization of high energy carbon-ion beam irradiation induced delayed flower senescence mutant in Lotus japonicus

Background Flower longevity is closely related to pollen dispersal and reproductive success in all plants, as well as the commercial value of ornamental plants. Mutants that display variation in flower longevity are useful tools for understanding the mechanisms underlying this trait. Heavy-ion beam irradiation has great potential to improve flower shapes and colors; however, few studies are available on the mutation of flower senescence in leguminous plants. Results A mutant (C416) exhibiting blossom duration eight times longer than that of the wild type (WT) was isolated in Lotus japonicus derived from carbon ion beam irradiation. Genetic assays supported that the delayed flower senescence of C416 was a dominant trait controlled by a single gene, which was located between 4,616,611 Mb and 5,331,876 Mb on chromosome III. By using a sorting strategy of multi-sample parallel genome sequencing, candidate genes were narrowed to the gene CUFF.40834, which exhibited high identity to ethylene receptor 1 in other model plants. A physiological assay demonstrated that C416 was insensitive to ethylene precursor. Furthermore, the dynamic changes of phytohormone regulatory network in petals at different developmental stages was compared by using RNA-seq. In brief, the ethylene, jasmonic acid (JA), and salicylic acid (SA) signaling pathways were negatively regulated in C416, whereas the brassinosteroid (BR) and cytokinin signaling pathways were positively regulated, and auxin exhibited dual effects on flower senescence in Lotus japonicus. The abscisic acid (ABA) signaling pathway is positively regulated in C416. Conclusion So far, C416 might be the first reported mutant carrying a mutation in an endogenous ethylene-related gene in Lotus japonicus, rather than through the introduction of exogenous genes by transgenic techniques. A schematic of the flower senescence of Lotus japonicus from the perspective of the phytohormone regulatory network was provided based on transcriptome profiling of petals at different developmental stages. This study is informative for elucidating the molecular mechanism of delayed flower senescence in C416, and lays a foundation for candidate flower senescence gene identification in Lotus japonicus. It also provides another perspective for the improvement of flower longevity in legume plants by heavy-ion beam.

Time Course Analysis of Genome-Wide Identification of Mutations Induced by and Genes Expressed in Response to Carbon Ion Beam Irradiation in Rice (Oryza sativa L.)

Heavy-ion irradiation is a powerful mutagen and is widely used for mutation breeding. In this study, using whole-genome sequencing (WGS) and RNA sequencing (RNA-seq) techniques, we comprehensively characterized these dynamic changes caused by mutations at three time points (48, 96, and 144 h after irradiation) and the expression profiles of rice seeds irradiated with C ions at two doses. Subsequent WGS analysis revealed that more mutations were detected in response to 40 Gy carbon ion beam (CIB) irradiation than 80 Gy of CIB irradiation at the initial stage (48 h post-irradiation). In the mutants generated from both irradiation doses, single-base substitutions (SBSs) were the most frequent type of mutation induced by CIB irradiation. Among the mutations, the predominant ones were C:T and A:G transitions. CIB irradiation also induced many short InDel mutations. RNA-seq analysis at the three time points showed that the number of differentially expressed genes (DEGs) was highest at 48 h post-irradiation. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis of the DEGs showed that the “replication and repair” pathway was enriched specifically 48 h post-irradiation. These results indicate that the DNA damage response (DDR) and the mechanism of DNA repair tend to quickly start within the initial stage (48 h) after irradiation.

A Mathematic Method to Adjust MLC Leaf End Position for Accuracy Dose Calculation in Carbon Ion Beam Radiation Therapy Treatment Planning System

IntroductionWe present a mathematic method to adjust the leaf end position for dose calculation correction in carbon ion radiation therapy treatment planning system. Methods and MaterialsA struggling range algorism of 400 MeV/n carbon ion beam in nine different multi-leaf collimator (MLC) materials was conducted to calculate the dose 50% point in order to derive the offset corrections in carbon ion treatment planning system (ciPlan). The visualized light field edge position in treatment planning system is denoted as Xtang.p and MLC position (Xmlc.p) is defined as the source to leaf end mid-point projection on axis for monitor unit calculation. The virtual source position of an energy at 400 MeV/n and struggling range in MLC at different field sizes were used to calculate the dose 50% position on axis. On-axis MLC offset (correction) could then be obtained from the position corresponding to 50% of the central axis dose minus the Xmlc.p MLC position. ResultsThe precise MLC position in carbon ion treatment planning system can be used an offset to do the correction. The offset correction of pure tungsten is the smallest among the others due to its shortest struggling range of carbon ion beam in MLC. The positions of 50% dose of all MLC materials are always located in between Xtang.p and Xmlc.p under the largest field of 12 cm by 12 cm. ConclusionsMLC offset should be adjusted carefully at different field size in treatment planning system especially of its small penumbra characteristic in carbon ion beam. It is necessary to find out the dose 50% position for adjusting MLC leaf edge on-axis location in the treatment planning system to reduce dose calculation error.