Background: Magnetic resonance image-guided radiation therapy (MR-IGRT) promises more precise and effective radiation treatments compared to conventional IGRT by using real-time on-board MR imaging. Under the influenc...Background: Magnetic resonance image-guided radiation therapy (MR-IGRT) promises more precise and effective radiation treatments compared to conventional IGRT by using real-time on-board MR imaging. Under the influence of a magnetic field, however, secondary electrons exiting a surface can be forced in a circular path and re-enter the medium, resulting in dose increase at a beam-exit surface, called the electron return effect (ERE). The purpose of the study is to compare the exit skin dose computed by Monte Carlo dose calculation with measurements using an adult anthropomorphic phantom and to measure the effect of skin dose reduction by adding 1 cm-thick bolus. Method: The plan was compared with measurements using an adult anthropomorphic phantom combined with radiochromic films and thermoluminescent dosimeters. We also measured the skin dose reduction by adding 1 cm-thick bolus on the frontal surface of the phantom. Results: We found that 1 cm-thick bolus reduced the skin dose by up to 20% both in measurements and calculations. The plan was found to overestimate the measured skin dose by about 10% and there was no significant difference in the bolus effect between the breast skin and the skin (without breast attachment) doses. Conclusion: In conclusion, we confirmed the ERE effect on the anthropomorphic phantom under the magnetic field and the exit skin dose reduction by adding a bolus. Skin dose measurements using anthropomorphic phantom may be helpful to evaluate more realistic skin dose and the bolus effect in the magnetic field.展开更多
目的:探讨3.0 T MR扩散张量成像在颈椎病诊断中的应用效果。方法:从2013年1月开始,至2015年1月结束,一共80例颈椎病患者,采用MR诊断仪对患者进行检查,比较颈椎病患者、健康体检者不同颈髓水平ADC值、FA值、颈髓长轴、前后径、左右径。结...目的:探讨3.0 T MR扩散张量成像在颈椎病诊断中的应用效果。方法:从2013年1月开始,至2015年1月结束,一共80例颈椎病患者,采用MR诊断仪对患者进行检查,比较颈椎病患者、健康体检者不同颈髓水平ADC值、FA值、颈髓长轴、前后径、左右径。结果:(1)在健康体检者中,C2-3、C4-5、C6-7之间ADC值、FA值、颈髓长轴、前后径、左右径无明显差异,无统计学意义,P>0.05;颈髓长轴、前后径、左右径之间两两对比,颈髓长轴值高于前后径和左右径,数据比较差异具有统计学意义,P<0.05。前后径和左右径之间对比,无明显差异,无统计学意义,P>0.05。(2)和对照组对比,A组ADC、FA、a1颈髓长轴无明显差异(P>0.05);a2前后径、a3左右径明显更大(P<0.05)。B组、C组、D组ADC值、FA值、颈髓长轴、前后径、左右径明显更大,数据比较差异明显,存在统计学意义,P<0.05.结论:采用扩散张量成像技术对颈椎病患者进行诊断,能够有效地显示颈椎压迫所致的脊髓微结构变化,具有较高的敏感性,3.0 T MR扩散张量成像在颈椎病诊断中的应用效果显著,能够弥补常规MRI难以定量分析颈椎微结构受压情况的缺点。展开更多
文摘Background: Magnetic resonance image-guided radiation therapy (MR-IGRT) promises more precise and effective radiation treatments compared to conventional IGRT by using real-time on-board MR imaging. Under the influence of a magnetic field, however, secondary electrons exiting a surface can be forced in a circular path and re-enter the medium, resulting in dose increase at a beam-exit surface, called the electron return effect (ERE). The purpose of the study is to compare the exit skin dose computed by Monte Carlo dose calculation with measurements using an adult anthropomorphic phantom and to measure the effect of skin dose reduction by adding 1 cm-thick bolus. Method: The plan was compared with measurements using an adult anthropomorphic phantom combined with radiochromic films and thermoluminescent dosimeters. We also measured the skin dose reduction by adding 1 cm-thick bolus on the frontal surface of the phantom. Results: We found that 1 cm-thick bolus reduced the skin dose by up to 20% both in measurements and calculations. The plan was found to overestimate the measured skin dose by about 10% and there was no significant difference in the bolus effect between the breast skin and the skin (without breast attachment) doses. Conclusion: In conclusion, we confirmed the ERE effect on the anthropomorphic phantom under the magnetic field and the exit skin dose reduction by adding a bolus. Skin dose measurements using anthropomorphic phantom may be helpful to evaluate more realistic skin dose and the bolus effect in the magnetic field.
文摘目的:探讨3.0 T MR扩散张量成像在颈椎病诊断中的应用效果。方法:从2013年1月开始,至2015年1月结束,一共80例颈椎病患者,采用MR诊断仪对患者进行检查,比较颈椎病患者、健康体检者不同颈髓水平ADC值、FA值、颈髓长轴、前后径、左右径。结果:(1)在健康体检者中,C2-3、C4-5、C6-7之间ADC值、FA值、颈髓长轴、前后径、左右径无明显差异,无统计学意义,P>0.05;颈髓长轴、前后径、左右径之间两两对比,颈髓长轴值高于前后径和左右径,数据比较差异具有统计学意义,P<0.05。前后径和左右径之间对比,无明显差异,无统计学意义,P>0.05。(2)和对照组对比,A组ADC、FA、a1颈髓长轴无明显差异(P>0.05);a2前后径、a3左右径明显更大(P<0.05)。B组、C组、D组ADC值、FA值、颈髓长轴、前后径、左右径明显更大,数据比较差异明显,存在统计学意义,P<0.05.结论:采用扩散张量成像技术对颈椎病患者进行诊断,能够有效地显示颈椎压迫所致的脊髓微结构变化,具有较高的敏感性,3.0 T MR扩散张量成像在颈椎病诊断中的应用效果显著,能够弥补常规MRI难以定量分析颈椎微结构受压情况的缺点。
