Objective To study the calculation of the room shielding thickness of tomotherapy accelerator,a new type of radiotherapy facility,especially the impact of the beam block on the shielding design.Methods According to the relevant standards,combined with the room geometry,the shielding thickness was calculated without the presence of the beam block,considering the primary beam,the scattered beam and leakage.Meanwhile,the shielding thickness was also calculated as comparison with the presence of the beam block,based on the characteristics of tomotherapy facility and its radiation field.Results There was statistical difference between the shielding thicknesses calculated with the presence of the beam block and those without the beam block,to the primary beam direction including the south wall,north wall,the roof and the floor,the shielding thickness were decreased by 95.59%,63.63% ,80.73%and 51.30% ,respectively.Conclusions For the tomotherapy accelerator,the beam block could be of great help to minify the shielding thickness of the room.The radiation field of the tomotherapy facility could be used for the calculation to improve accuracy,and the shielding thickness can also be estimated by subtracting the initial shielding thickness without beam block of the beam block equivalent thickness in the primary beam direction alternatively.

Objective To provide evidence for a more reasonable method of determining red bone marrow dose by analyzing and comparing existing simulation methods.Methods By utilizing Monte Carlo simulation software MCNPX,the absorbed doses of red hone marrow of Rensselaer Polytechnic Institute (RPI)adult female voxel phantom were calculated throush 4 different methods:direct energy deposition.dose response function(DRF),King-Spiers factor method and mass-energy absorption coefficient (MEAC).The radiation sources were defined as infinite plate.sources with the energy ranging from 20 keV to 10 MeV.and 23 sources with different energies were simulated in total.The source was placed right next to the front of the RPI model to achieve a homogeneous anteroposterior radiation scenario.The results of different simulated photon energy sources through different methods were compared.Results When the photon energy was lower than 100 key,the direct energy deposition method gave the highest result while the MEAC and King-Spiers factor methods showed more reasonable results.When the photon energy was higher than 150 keV taking into account of the higher absorption ability of red bone marrow at highcr photon energy,the result of the King-Spiers factor method was larger than those of other methods.Conclusions The King-Spiers factor method might be the most reasonable method to estimate the red bone marrow dose from external radiation.

Objective To evaluate and compare the efficacy and safety of laparoscopic surgery in the treatment of elder colorectal cancer patients.Methods Selected the retrospective or prospective studies which were retrieved in Pubmed,web of Science,Embase as laparoscopic,laparoscopic colectomy,colorectal cancer,rectal cancer,octogenarian,elderly published between Jan.2000 and May 2017.Data regarding operative indexes,postoperative complications and long term outcomes were analyzed by Stata12.0 software.Results A total of 18 articles,included 3 162 patients,were enrolled in this study.The Meta-analysis indicated that there were no significant differences of less blood loss,postoperative wound infection,bowel obstruction and cardiovascular complications in laparoscopic surgery group except the operative time (P ＜ 0.05).No significant difference was found in the number of dissected lymph node,pneumonia,overall survival and disease free survival (P ＞ 0.05).Conclusion With advantages of rapid postoperative recovery and fewer complications,laparoscopic radical resection for colorectal cancer in elderly patients is safe and effective.

Objective To quantitatively study the influence of changes in probe position on the quality control test results of dental panoramic radiography and to provide a reference for analyzing the sources of deviations in quality control test results. Methods Eight different models of dental panoramic X-ray machines were selected for this study. The film analysis method was used to determine the position of the central axis of the main beam on the image detector. The position of the probe was accurately controlled through an auxiliary moving device. The tube voltage, radiation output, and half-value layer of the useful beam were measured for positions at the center of the beam; 1 cm upward, downward, left, and right from the center of the beam; and 2 cm upward, downward, left, and right from the center of the beam. Results The tube voltage, radiation output, and half-value layer had a maximum value at the center of the beam, with a decrease in the value as the position deviated from the center. There were significant differences in the probe position sensitivity between different models of dental panoramic radiography equipment. A 2 cm deviation in the probe position resulted in an impact on the measured tube voltage of less than 5.3 kV (5.8%) for less sensitive equipment. A 2 mm deviation in the probe position resulted in an impact on the measured tube voltage of less than 5.4 kV (6.0%) for sensitive equipment. Conclusion The probe position can lead to deviation in the quality control test results of dental panoramic photography. Therefore, determining the position of the central axis of the main beam on the image detector for accurate positioning of the probe is crucial for quality control testing.

The radiation risk caused by CT examination is of great concern. Organ dose is considered to be the most significant technical parameter for quantifying the patient radiation dose and assessing the corresponding risk. At present, the methods to obtain patient organ dose caused by CT examination mainly include physical phantom measurement, direct human body measurement, dose conversion coefficient, Monte Carlo simulation, and dose calculation software. Although different methods have their own characteristics and application, the individualization of organ dose is always the goal of radiation protection and dosimetry research. Patient-specific phantom developed with artificial intelligence and GPU-accelerated Monte Carlo simulation make it possible to calculate the patient-specific organ dose, and the patient-specific organ dose extrapolated by the CT detector signal provides a new solution.