ABSTRACT
Objective To evaluate the effect of the thickness and area of the cavity between bolus and skin upon the dose deposition in the shallow tissues.Methods The linear accelerator head model of 6 MV X ray was constructed using Geant4,which simulated the accelerator working condition of 10 cm× 10 cm field and recorded the information of emergent particles as phase space file.A water phantom of 30 × 30 × 30 cm3 was designed at the SAD level.A 30 cm × 30 cm × 1 cm water film was constructed adjacent to or with different cavities to the upper surface of the phantom.The phase space file was utilized as particle source to simulate the particle transport process.The axis depth dose distribution and lateral dose profiles in the center area of the field at a depth of 1 mm,5 mm,9 mm,15 mm and 21 mm of the phantom were obtained,respectively.The simulated data obtained from water film with different cavities were compared with those of adjacent to the water phantom.Results When the cavity was ≤ 5 mm,the cavity exerted slight effect.When the thickness was increased,the maximum dose depth (Dmax) was increased,the PDD at Dmax (PD Dmax) became less,the depth of influenced lateral dose profiles was increased and the dose in the center area was decreased.Along with the increase of cavity area,the Dmax was initially increased and then decreased,the PD Dmax was at first decreased and subsequently increased,the depth of influenced lateral dose profile was initially increased and then decreased,the dose in the center area was first decreased and subsequently increased.The lateral dose profile distant from the cavity or located at a depth ≥ 15 mm was almost not affected by the cavity.Conclusion The thickness of the cavity between bolus and skin should be less than 5 mm and the cavity area should be small as possible.
ABSTRACT
Objective To investigate the effect of cavity thickness, area and distance under the bolus upon the dose in the superficial tissues. Methods An accelerator model was constructed based on Geant4.The model accuracy was validated by the comparison of the calculated data with the measured data. A 30×30×30 cm3 water phantom with the upper surface located at the isocenter level and a 30×30×1 cm3 water film were constructed. Different models with the water film close to or different cavities with the water phantom were established. Under the 10×10 cm2 field with 6 MV X-ray beam,the central axis depth dose distribution and the lateral dose profiles at a depth of 0. 1 cm ( profile1) of the models with different cavities were calculated. The calculated data of different model with the water film close to or different cavities with the water phantom were statistically compared. Results When the cavity thickness was ≤ 0. 5 cm, the cavity exerted slight effect upon the depth of maximum dose ( Dmax ) and superficial dose. As the cavity thickness was increased,the Dmax was also increased,the PDD at 0. 1 cm ( PDD1) was decreased rapidly and the profile1 was increased from the cavity center to the edge. Along with the increase of cavity area,the Dmax was initially increased and then decreased,whereas the PDD1 was first decreased followed by an increase. When the cavity area was small,the profile1 was gradually increased from the cavity center to the edge. When the cavity area was large,the profile1 was initially decreased and subsequently increased. When the distance was ≥0. 2 cm,it was qualified for the clinical requirement and it exerted no effect when the distance was≥1. 0 cm. The profile1 distant from the cavity was not affected. Conclusion The cavity under the bolus should be minimized to reduce the cavity thickness,area and distance as possible.
ABSTRACT
Objective To evaluate the radiosensitization effect of low-temperature plasma on HepG2, A549, and HeLa cells.Methods Cells were divided into three groups, radiation group (R) , plasma treatment group(P), and plasma plus radiation group (P + R).After radiation, cell survival was detected by a cloning assay.Cell cycle distribution, apoptosis and ROS content were tested by flow cytometry.Western blot was used to measure the expressions of Caspase-3 and Bcl-2.Results Lowtemperature plasma showed radiosensitization effects on three different human malignant cell lines with a sensitivity enhancement ratio(SERD0) of 1.28,1.32 and 1.29.respectively.In these three different human malignant cell lines, compared with radiation alone group (R) , the G2/M arrest, apoptosis rate and ROS level in the group P + R were enhanced (the prolongation of G2/M arrest: t =9.52, 8.24, 9.53, P ＜ 0.05;the apoptosis rate: t =10.67, 38.56, 6.74, P ＜0.05;ROS content: t =9.41, 15.42, 13.53, P ＜0.05).In HepG2 cells and A549 cells, compared with group P, the prolongation of G2/M arrest, the apoptosis rate and ROS content of group P + R were enhanced (the prolongation of G2/M arrest: t =8.75, 20.37, P＜0.05;the apoptosis rate: t =8.43, 9.99, P ＜0.05;ROS content: t =4.82, 5.27, P ＜ 0.05).The expression level of Bcl-2 protein was downregulated in group P + R;by contrast, the expression level of Caspase-3 protein in group P + R was upregulated.Conclusions Low-temperature plasma can increase the radiosensitization of HepG2, A549 and HeLa cells with the enhancement of G2/M phase arrest, apoptosis induction and ROS generation.