Objective:To develop a spot scanning carbon ion beam model based on Monte Carlo code FLUKA and verify the accuracy of physical dose.Methods:A geometric model of the treatment nozzle was established in FLUKA. Various parameters such as monoenergy nominal energy, Gaussian energy spectrum distribution, initial spot size, and beam angular distribution in the model were adjusted to match the reference data of integral depth dose (IDD) and in-air spot size measuremed experimentally. Carbon ion beam plans were generated by using the treatment planning system (TPS). The difference in output dose distribution between FLUKA and TPS was compared by the gamma analysis.Results:The differences in Bragg peak width, beam range, and distal falloff width extracted from the IDD curve between the FLUKA model and measured vaues were less than 0.1 mm, with the maximum difference in spot sizes of 0.17 mm. Under the criterion of 2 mm/2% in all the simulations, 2D- and 3D-γ pass rates were all above 95%.Conclusions:An accurate spot scanning carbon beam model was developed based on the Monte Carlo code FLUKA. It has the potential to be used for not only the verification of clinical treatment plans, but also the development of new ion beam therapy equipment and the calculation of biologically effective dose.

Objective:To develop and validate a structure for broadening the Bragg peak to improve the efficiency and conformality of particle radiotherapy.Methods:Techniques of random stacking and regular stacking were employed to fabricate the mesh-stacked porous structure (MPS). In each layer of the grid, the thickness, line width and spacing were set at 0.1 mm, 0.1 mm and 0.5 mm, respectively, resulting in a total size of 10 cm ×10 cm. Monte Carlo code FLUKA was performed to simulate the transportation of 196 MeV/u carbon ion beam and a 105 MeV proton beam through the MPS. Dose distribution, fluence homogeneity, and modulation stability of the modulated beams were evaluated. Moreover, the modulation effect of MPS in clinical radiotherapy plans for nasopharyngeal carcinoma (63 Gy in 21 fractions), lung cancer (77 Gy in 22 fractions) and prostate cancer (70.4 Gy in 16 fractions) was also evaluated, respectively.Results:The MPS was capable of broadening the Bragg peak width by 1.73 mm for proton beams and 2.95 mm for carbon ion beams. For different entrance positions, regular stacking of more than 10 layers could reduce the modulation power difference of MPS to within 5%. For MPS with 30 layers of regular stacking, the modulated fluence homogeneity could achieve a value of less than 3% by transporting 18 cm distance in air. When comparing to the clinically used ripple filters, MPS reduced the isocenter spot size of proton beams by 0.91 mm. In the comparison study of the treatment plan for nasopharyngeal carcinoma, the use of MPS could shorten the treatment time by 213 s (37%) and reduce the maximum dose to the brainstem by 3.28 Gy (7.5%).Conclusions:MPS effectively broadens the Bragg peak of particle beams and improves the efficiency of clinical radiotherapy. Regularly stacked MPS demonstrates robust modulation stability, and the modulated beam achieves relatively well fluence homogeneity, making it a promising clinical application for closer to the patients and reducing lateral scattering.