Nuclear-interaction correction of integrated depth dose in carbon-ion radiotherapy treatment planning
Nuclear-interaction correction of integrated depth dose in carbon-ion radiotherapy treatment planning
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DOI：
10.1088/0031-9155/60/1/421
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发表时间：
2015-01-07
影响因子：
3.5
通讯作者：
Furukawa, T.
中科院分区：
文献类型：
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作者：
Inaniwa, T.;Kanematsu, N.;Furukawa, T.
在带电粒子治疗的治疗计划中，组织异质性通常被建模为具有不同密度的水，即停止有效密度rho(S)，并相应地应用水中测量的积分深度剂量(IDD)来计算患者剂量。由于身体组织的化学成分与水的化学成分不同，这种近似会导致剂量计算错误，特别是由于核相互作用的差异。在这里，我们提出并验证了一种 IDD 校正方法，用于纠正患者剂量计算中的这些错误。为了准确处理核相互作用，将患者的 rho(S) 转换为核有效密度 rho(N)，定义为使用最近制定的两者之间的半经验关系，组织中核相互作用的概率与水中核相互作用的概率之比。衰减校正因子 phi(p)(w) 定义为患者体内一次碳离子的衰减与水中的一次碳离子的衰减之比，是根据 rho(N) 沿光束路径的线性积分计算得出的。在我们的治疗计划系统中，碳离子束根据其横束尺寸被建模为由三个组件组成：初级碳离子、较重的碎片和较轻的碎片。我们将初级碳离子对 IDD 的剂量贡献修正为与 phi(p)(w) 成正比，并将较轻碎片的剂量贡献修正为与 phi(p)(w) 成反比。我们测试了一些非水材料的校正方法，例如牛奶、猪油、乙醇和磷酸钾（K2HPO4）水溶液，使用非扫描和扫描碳离子束。在非扫描光束中，穿透150毫米厚猪油层的光束与穿透相应厚度水的光束之间的IDD差异为-4%，而穿透150毫米厚40% K2HPO4层的IDD差异为+6%。通过校正方法准确预测了观察到的差异。对于所有材料及其组合，校正后的 IDD 与测量值的误差在 +/- 1% 范围内。在扫描光束中，对于 150 毫米厚的 40% K2HPO4 层，目标剂量的剂量估计误差达 4%。通过校正方法，误差显着减小。该方法的计划剂量分布与所有材料的目标剂量测量结果一致，不仅在目标区域，而且在平台和碎片尾部区域都在目标剂量的+/-1.5%以内。我们在一些非水材料中测试了IDD的校正方法，以验证该方法能够提供碳离子放射治疗计划所需的准确性和简单性。
In treatment planning of charged-particle therapy, tissue heterogeneity is conventionally modeled as water with various densities, i.e. stopping effective densities rho(S), and the integrated depth dose measured in water (IDD) is applied accordingly for the patient dose calculation. Since the chemical composition of body tissues is different from that of water, this approximation causes dose calculation errors, especially due to difference in nuclear interactions. Here, we propose and validate an IDD correction method for these errors in patient dose calculations.For accurate handling of nuclear interactions, rho(S) of the patient is converted to nuclear effective density rho(N), defined as the ratio of the probability of nuclear interactions in the tissue to that in water using a recently formulated semi-empirical relationship between the two. The attenuation correction factor phi(p)(w), defined as the ratio of the attenuation of primary carbon ions in a patient to that in water, is calculated from a linear integration of rho(N) along the beam path. In our treatment planning system, a carbon-ion beam is modeled to be composed of three components according to their transverse beam sizes: primary carbon ions, heavier fragments, and lighter fragments. We corrected the dose contribution from primary carbon ions to IDD as proportional to phi(p)(w), and corrected that from lighter fragments as inversely proportional to phi(p)(w). We tested the correction method for some non-water materials, e.g. milk, lard, ethanol and water solution of potassium phosphate (K2HPO4), with un-scanned and scanned carbon-ion beams.In un-scanned beams, the difference in IDD between a beam penetrating a 150 mm-thick layer of lard and a beam penetrating water of the corresponding thickness amounted to -4%, while it was +6% for a 150 mm-thick layer of 40% K2HPO4. The observed differences were accurately predicted by the correction method. The corrected IDDs agreed with the measurements within +/- 1% for all materials and combinations of them. In scanned beams, the dose estimation error in target dose amounted to 4% for a 150 mm-thick layer of 40% K2HPO4. The error is significantly reduced with the correction method. The planned dose distributions with the method agreed with the measurements within +/- 1.5% of target dose for all materials not only in the target region but also in the plateau and fragment-tail regions.We tested the correction method of IDD in some non-water materials to verify that this method would offer the accuracy and simplicity required in carbon-ion radiotherapy treatment planning.