Monte Carlo calculations of correction factors for plastic phantoms in clinical photon and electron beam dosimetry
Monte Carlo calculations of correction factors for plastic phantoms in clinical photon and electron beam dosimetry
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DOI：
10.1118/1.3151809
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发表时间：
2009-07-01
期刊：
影响因子：
3.8
通讯作者：
Oguchi, Hiroshi
中科院分区：
文献类型：
--
作者：
Araki, Fujio;Hanyu, Yuji;Oguchi, Hiroshi
本研究的目的是使用EGSnrc蒙特卡罗程序系统计算临床光子和电子束剂量学中塑料水(PW)和塑料水诊断治疗(PWDT)模体的校正因子。计算了几种常用的具有不同壁面材料的Farmer型电离室在4-18 MV光子束范围内PW和PWDT的水塑性电离转换因子k(Pl)。对于电子束，还结合NACP-02和Roos平面平行电离室计算了两个模体在4-18 MeV范围内的深度标度因子c(Pl)和与腔室有关的通量修正因子h(Pl)。平面平行腔室的h(Pl)值由水或塑料材料组合的电子通量修正因子Phi(W)(Pl)和壁面修正因子P(wall，w)和P(wall，pl)来估算。通过与实测值的比较，验证了计算的k(Pl)和h(Pl)值。对于光子束中的PW和PWDT，为Farmer类型的腔计算的一组k(Pl)值等于0.5%以内的单位。K(Pl)值在其与测量数据的组合不确定度内也是一致的。对于电子束，在4-18 MeV的范围内，PW和PWDT计算的c(Pl)值分别为0.998至1.000和0.992至0.997。在4-18 MeV的参考深度范围内，PW和PWDT的Phi(W)(Pl)值分别为0.998-1.001和1.004-1.001。对于平面平行室，水和塑料之间的P(壁面)差最大为0.8%。最后，对塑料材料评估的h(Pl)值对于NACP-02和Roos密封室而言等于0.6%内的单位。H(Pl)值在其与测量数据的组合不确定度内也是一致的。电离室测量的PW和PWDT塑料材料对水的吸收剂量与水中的剂量相当于1%以内。因此，这两个模体都可以用来代替水进行光子和电子剂量测定。
The purpose of this study is to calculate correction factors for plastic water (PW) and plastic water diagnostic-therapy (PWDT) phantoms in clinical photon and electron beam dosimetry using the EGSnrc Monte Carlo code system. A water-to-plastic ionization conversion factor k(pl) for PW and PWDT was computed for several commonly used Farmer-type ionization chambers with different wall materials in the range of 4-18 MV photon beams. For electron beams, a depth-scaling factor c(pl) and a chamber-dependent fluence correction factor h(pl) for both phantoms were also calculated in combination with NACP-02 and Roos plane-parallel ionization chambers in the range of 4-18 MeV. The h(pl) values for the plane-parallel chambers were evaluated from the electron fluence correction factor phi(w)(pl) and wall correction factors P(wall,w) and P(wall,pl) for a combination of water or plastic materials. The calculated k(pl) and h(pl) values were verified by comparison with the measured values. A set of k(pl) values computed for the Farmer-type chambers was equal to unity within 0.5% for PW and PWDT in photon beams. The k(pl) values also agreed within their combined uncertainty with the measured data. For electron beams, the c(pl) values computed for PW and PWDT were from 0.998 to 1.000 and from 0.992 to 0.997, respectively, in the range of 4-18 MeV. The phi(w)(pl) values for PW and PWDT were from 0.998 to 1.001 and from 1.004 to 1.001, respectively, at a reference depth in the range of 4-18 MeV. The difference in P(wall) between water and plastic materials for the plane-parallel chambers was 0.8% at a maximum. Finally, h(pl) values evaluated for plastic materials were equal to unity within 0.6% for NACP-02 and Roos chambers. The h(pl) values also agreed within their combined uncertainty with the measured data. The absorbed dose to water from ionization chamber measurements in PW and PWDT plastic materials corresponds to that in water within 1%. Both phantoms can thus be used as a substitute for water for photon and electron dosimetry.