R(50) as a beam quality specifier for selecting stopping-power ratios and reference depths for electron dosimetry
R(50) as a beam quality specifier for selecting stopping-power ratios and reference depths for electron dosimetry
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DOI：
10.1118/1.597893
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发表时间：
1996-03-01
期刊：
影响因子：
3.8
通讯作者：
Rogers, DWO
中科院分区：
文献类型：
--
作者：
Burns, DT;Ding, GX;Rogers, DWO
对于放射治疗中的电子束参考剂量测定，表明通过选择参考深度为d（ref）= 0.6 R（50）-0.1 cm，其中R（50）是以厘米为单位的半值深度，d（ref）处的Spencer-Attix水与空气停止功率比由下式给出：（（L）除以bar/rho）（空气）（w）=1.2534-0.1487（R（50））（0.2144）。这是根据24个临床射束的真实蒙特卡罗模拟获得的（（L）/bar/rho）（空气）（w）数据得出的。该表达式与Monte Carlo计算的均方根偏差为0.16%，最大偏差为0.26%。该方法充分考虑了相同R（50）的真实的电子束之间的光谱差异，并且允许在标准实验室处的校准剂量校准容易且准确地转移到参考临床射束。当选择参考深度作为剂量最大值的深度时，使用单个参数来指定（（L）over bar/rho）（空气）（w），而不是所需的两个参数（R（50）和深度），有可能大大简化电子束剂量测定协议，并允许使用类似的形式来进行光子和电子束剂量测定。为了将深度-电离曲线转换成深度-剂量曲线，给出了（（L）/巴/ρ）（空气）（w）作为R（50）和深度的函数的精度稍低但一般的表达式。
For electron beam reference dosimetry in radiotherapy, it is shown that by choosing the reference depth as d(ref)=0.6R(50)-0.1 cm, where R(50) is the half-value depth in centimeters, the Spencer-Attix water-to-air stopping-power ratio at d(ref) is given by ((L) over bar/rho)(air)(w)=1.2534-0.1487 (R(50))(0.2144). This is derived from data for ((L) over bar/rho)(air)(w) obtained from realistic Monte Carlo simulations for 24 clinical beams. The rms deviation of this expression from the Monte Carlo calculations is 0.16%, with a maximum deviation of 0.26%. This approach fully takes into account the spectral differences between real electron beams of the same R(50) and allows an absorbed-dose calibration at a standards laboratory to be easily and accurately transferred to a reference clinical beam. Using a single parameter to specify ((L) over bar/rho)(air)(w), rather than the two parameters (R(50) and depth) needed when the reference depth is chosen as the depth of dose maximum, has the potential to greatly simplify electron beam dosimetry protocols and allows the use of a similar formalism for photon and electron beam dosimetry. For use in converting a depth-ionization curve into a depth-dose curve, a somewhat less accurate but general expression for ((L) over bar/rho)(air)(w) as a function of R(50) and depth is presented.