Objective To study the spectrum structure of X-ray and simplify the description method of it. Methods By the general program of Monte Carlo Geant4 to study X-ray spectrum structure and angular distribution of X-ray energy spectrum. Results The results of percentage depth doses and profile curves at different depths of any radiation fields in water phantom calculated by Monte Carlo Geant4 were consistent with the measurements. Conclusions In radiotherapy, X-ray with same nominal energy have very similar dosimetry characteristics, this indicates they have very similar energy spectrum and angular distribution of spectrum. the differences of dosimetric details reflect the different details of the X-ray spectrum structure and angular distribution of X-ray energy spectrum. These studies have very important significances to rapidly build precise virtual source modeling for Monte Carlo calculation based on dose curves measurements in water phantom.

ObjectiveTo analyze the effects of high-order scattered X-ray in dose calculation in radiotherapy,to resolve the problem of correcting the dose contribution of secondary and high-order scattering X-ray to the primary scattered X ray,and to provide a support for photon fast dose calculation method of Monte Carlo.MethodsBy the theory of cross-section in interaction between X-ray with material and Monte Carlo calculating results,to analysis the relative importance of primary scattered X-ray,secondary and high-order scattered of X-ray in dose calculation.ResultsThe contribution of secondary and high-order scattered X-ray to dose calculation was very small,it can be corrected to the primary scattered X-ray with a correction factor.ConclusionsThe results show that we can obtain a precise dose calculation for radiotherapy by only to tracking the contribution of primary X-rays and primary scattering X-ray,so,to establishing the database for primary scattering X-ray by Monte Carlo methods is important for fast dose calculation of Monte Carlo method.

Objective To investigate analgesic effects of the selective blocking of descending facilitation targeting μ opioid receptor positive neurons in the rostral ventromedial medulla ( RVM) in a rat model of bone cancer pain. Methods Forty-eight adult female Wistar rats weighing 180-200 g were randomly divided into 6 groups: group Ⅰ control ( n = 3) ;group Ⅱ bone cancer pain induced by intra-tibia inoculation of Walker 256 mammary gland carcinoma cells ( n = 9) ;group Ⅲ-Ⅵ received a single intra-RVM micro-injection of PBS (group Ⅲ), dermorphin (group Ⅳ) , saporin (group Ⅴ) and dermorphin-saporin ( group Ⅵ) respectively at 28 days before intra-tibia inoculation ( n = 9 each) . Starting from 3 to 20 days after intra-tibia inoculation, mechanical allodynia was assessed and recorded. The animals were sacrificed on 7, 14 and 20 days after intra-tibia inoculation, after repetitive non-noxious tactile stimulation of the hindpaw. The total number of Fos-positive neurons in the spinal dorsal horn was measured as a marker indicative of central sensitization. Results The animals developed nociceptive hypersensitivity after intra-tibia cancer cell inoculation in group Ⅱ -Ⅵ . Nociceptive hypersensitivity was significantly decreased during 4-7 days after the onset of nociception in group Ⅵ (dermorphin-saporin). The number of Fos positive neurons in bilateral spinal dorsal horn was significantly increased by intra-tibia inoculation of cancer cells in group Ⅱ-Ⅵ as compared with control group and was significantly lower at day 14 and 20 after inoculation in group Ⅵ (dermorphin-saporin) than in group Ⅱ - Ⅴ.Conclusion Selective blocking of descending facilitation targeting μ opioid receptor positive neurons in RVM can effectively reduce nociceptive hypersensitivity induced by intra-tibia inoculation of Walker56 mammary gland carcinoma cells.