Chica U, Anguiano M, Lallena A M
Departamento de Física Atómica, Molecular y Nuclear, Universidad de Granada, E-18071 Granada, Spain.
Phys Med Biol. 2008 Dec 7;53(23):6963-77. doi: 10.1088/0031-9155/53/23/020. Epub 2008 Nov 12.
We have studied the procedure commonly recommended by dosimetry protocols for the determination of the absorbed dose in water for low-energy x-rays beams, generated with potentials up to 150 kVp. X-ray beams with different spectra obtained with the XCOMP5R code were transported using the Monte Carlo code PENELOPE in order to calculate backscatter factors and mass-energy absorption coefficients. We have analyzed the uncertainty in the absorbed doses, calculated using the half-value layer to characterize the x-ray beams, due to the uncertainties in both backscatter factors and mass-energy absorption coefficients. We have found that this uncertainty is larger than 5% and can reach values above 11% for some HVL(1) values. The characterization of these doses with the homogeneity coefficient or the generating potential, in addition to the half-value layer is also studied. Using HVL(1) and the kVp, the absorbed dose to water can be reproduced to within 3% for all spectra.
我们研究了剂量测定协议通常推荐的用于确定能量高达150 kVp的低能X射线束在水中吸收剂量的程序。使用XCOMP5R代码获得的具有不同光谱的X射线束通过蒙特卡罗代码PENELOPE进行传输，以计算反向散射因子和质能吸收系数。我们分析了由于反向散射因子和质能吸收系数的不确定性，使用半值层来表征X射线束时计算出的吸收剂量的不确定性。我们发现这种不确定性大于5%，对于某些半值层（HVL(1)）值，可达到11%以上。除了半值层之外，还研究了使用均匀性系数或产生电位对这些剂量进行表征的情况。使用HVL(1)和千伏峰值（kVp），对于所有光谱，水的吸收剂量可在3%的范围内再现。
