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Objective To investigate the effect of various frequencies of bolus use on the superficial dose of volumetric modulated arc therapy after modified radical mastectomy for breast cancer.Methods Based on the computed tomography images of a female anthropomorphic breast phantom, a 0.5 cm silicone-based 3D-printed bolus was created. Nine points evenly distributed on the breast skin were selected for assessing the skin dose, and a volume of subcutaneous lymphatic drainage of the breast (noted as ROI2-3) was delineated for assessing the chest wall dose. The treatment plans with and without bolus (plan_wb and plan_nb) were separately designed using the prescription of 50 Gy in 25 fractions following the standard dose constraints of the adjacent organ at risk. To characterize the accuracy of treatment planning system (TPS) dose calculations, the doses of the nine points were measured five times by thermoluminescence dosimeters (TLDs) and then were compared with the TPS calculated dose.Results Compared with Plan_nb (144.46 ± 10.32 cGy), the breast skin dose for plan_wb (208.75 ± 4.55 cGy) was significantly increased (t = −18.56, P< 0.001). The deviation of skin dose was smaller for Plan_wb, and the uniformity was significantly improved. The calculated value of TPS was in good agreement with the measured value of TLD, and the maximum deviation was within 5%. Skin and ROI2-3 doses were significantly increased with increasing frequencies of bolus applications. The mean dose of the breast skin and ROI2-3 for 15 and 23 times bolus applications were 45.33 Gy, 50.88 Gy and 50.36 Gy, 52.39 Gy, respectively.Conclusion 3D printing bolus can improve the radiation dose and the accuracy of the planned dose. Setting Plan_wb to 15 times for T1-3N+ breast cancer patients and 23 times for T4N+ breast cancer patients can meet the clinical need. Quantitative analysis of the bolus application frequency for different tumor stages can provide a reference for clinical practice.

The shear viscosity of nanofluids is sensitive to the size and concentration of the added nano particles. Using equilibrium molecular dynamics (MD) simulations we studied the particle size, particle concentration and temperature dependence of the shear viscosity of Al 2 O 3 nanofluids. Larger viscosity was predicted for the nanofluids with smaller particle size, higher particle concentration, and lower temperature, which reproduced the experimental trends. The increased viscosity is attributed to the particle–water interaction. Calculations at the density functional theory level conform that the interaction energy between Al 2 O 3 particle and water molecule is stronger than that between water molecules. Based on the simulated results an expression was proposed to describe the mixed effect of particle size, particle concentration and temperature on the viscosity of Al 2 O 3 nanofluids. [ABSTRACT FROM AUTHOR]