Sessions J B, Roshau J N, Tressler M A, Hintenlang D E, Arreola M M, Williams J L, Bouchet L G, Bolch W E
Department of Nuclear and Radiological Engineering, University of Florida, Gainesville 32611-8300, USA.
Med Phys. 2002 Jun;29(6):1080-9. doi: 10.1118/1.1481516.
Pediatric radiographic examinations yield medical benefits and/or diagnostic information that must be balanced against potential risk from patient radiation exposure. Consequently, clinical tools for measuring internal organ dose are needed for medical risk assessment. In this study, a physical phantom and Monte Carlo simulation model of the newborn patient were developed based upon their stylized mathematical expressions (ORNL and MIRD model series). The physical phantom was constructed using tissue equivalent substitutes for soft tissue, lung, and skeleton. Twenty metal-oxide-semiconductor field effect transistor (MOSFET) dosimeters were then inserted at three-dimensional positions representing the centroids of organs assigned in the ICRP's definition of the effective dose. MOSFET-derived point estimates of organ dose were shown to be in reasonable agreement with Monte Carlo estimates for representative newborn head, chest, and abdomen radiographic exams. Ratios of average organ dose assessed via MCNP simulations to the MOSFET-derived point doses (point-to-organ dose scaling factors, SF(POD)) are tabulated for subsequent use in clinical irradiations of the newborn phantom/MOSFET system. Values of SF(POD) indicate that MOSFET measurements of point dose for in-field exposures need to be adjusted only to within 10% to report volume-averaged organ dose. Larger adjustments to point doses are noted for organs out-of-field. For walled organs, point estimates of organ dose at the content centroid are shown to underestimate the average wall dose when the organ is within the primary field: SF(POD) of 1.19 for the stomach (AP chest exam), and SF(POD) of 1.15 for the urinary bladder (AP abdomen exam).
儿科放射检查可产生医疗效益和/或诊断信息，必须将其与患者辐射暴露的潜在风险进行权衡。因此，医学风险评估需要用于测量内部器官剂量的临床工具。在本研究中，基于新生儿患者的简化数学表达式（橡树岭国家实验室和医学内照射剂量模型系列）开发了物理体模和蒙特卡罗模拟模型。该物理体模使用软组织、肺和骨骼的组织等效替代物构建。然后将20个金属氧化物半导体场效应晶体管（MOSFET）剂量计插入到代表国际辐射防护委员会（ICRP）有效剂量定义中所指定器官质心的三维位置。对于代表性的新生儿头部、胸部和腹部放射检查，MOSFET得出的器官剂量点估计值与蒙特卡罗估计值显示出合理的一致性。通过MCNP模拟评估的平均器官剂量与MOSFET得出的点剂量之比（点到器官剂量缩放因子，SF(POD)）列于表格中，供后续用于新生儿体模/MOSFET系统的临床照射。SF(POD)的值表明，对于场内照射，MOSFET测量的点剂量仅需调整至10%以内即可报告体积平均器官剂量。对于场外器官，点剂量的调整幅度更大。对于有壁器官，当器官位于主射野内时，器官内容质心处的器官剂量点估计值被证明低估了平均壁剂量：胃部（前后位胸部检查）的SF(POD)为1.19，膀胱（前后位腹部检查）的SF(POD)为1.15。
