On the clinical spatial resolution achievable with protons and heavier charged particle radiotherapy beams
On the clinical spatial resolution achievable with protons and heavier charged particle radiotherapy beams
复制标题
DOI：
10.1088/0031-9155/54/11/n01
复制
发表时间：
2009-06-07
影响因子：
3.5
通讯作者：
Andreo, Pedro
中科院分区：
文献类型：
--
作者：
Andreo, Pedro
通常声称质子和轻离子束治疗可以实现的“亚毫米精度”使用蒙特卡罗代码SHIELD-HIT针对广泛的能量范围进行分析。根据水和人体组织的平均激发能以及器官和组织的组成的可能值和不确定性范围，可以得出结论，出于治疗计划的目的，精确度声明值得仔细重新考虑。发现ICRU报告37、49和73中所述的水的I值范围（1984，1993和2005）对于碰撞阻止本领公式，即67 eV，75 eV和80 eV，产生质子和较重带电粒子的布拉格峰深度的扩展（碳离子），这也被发现是能量依赖性的，由于其他能量损失竞争相互作用机制。在质子和具有类似实际范围的碳离子中，扩散是类似的。虽然在开发经验剂量计算模型时可以使用水中精确的深度剂量分布测量，但扩散的能量依赖性造成了很大的限制。在体内人体组织的情况下，分布测量是不可行的，这个问题造成了重大的限制。除了由于其I值的当前可接受的不确定性引起的扩散之外，还证明了由于软组织的不同组成引起的布拉格峰深度的扩散，即使对于在临床实践中可以被认为实际上相同的病例也是如此。对于这些，发现的扩散与水的扩散相似，甚至更大，为国际建议提供了支持，建议人体组织成分不应被赋予物理常数的地位。结果表明，由于“固有的基本物理不确定性”，即使是在水模的情况下，也有必要增加临床靶体积的边缘，增加了由于解剖或治疗策略原因而在正常临床实践中通常考虑的边缘。甚至为了达到“亚厘米精度”，也可能需要个体化患者沿着整个射束路径确定组织成分，而不仅仅是CT Hounsfield数。
The 'sub-millimetre precision' often claimed to be achievable in protons and light ion beam therapy is analysed using the Monte Carlo code SHIELD-HIT for a broad range of energies. Based on the range of possible values and uncertainties of the mean excitation energy of water and human tissues, as well as of the composition of organs and tissues, it is concluded that precision statements deserve careful reconsideration for treatment planning purposes. It is found that the range of I-values of water stated in ICRU reports 37, 49 and 73 (1984, 1993 and 2005) for the collision stopping power formulae, namely 67 eV, 75 eV and 80 eV, yields a spread of the depth of the Bragg peak of protons and heavier charged particles (carbon ions) of up to 5 or 6 mm, which is also found to be energy dependent due to other energy loss competing interaction mechanisms. The spread is similar in protons and in carbon ions having analogous practical range. Although accurate depth-dose distribution measurements in water can be used at the time of developing empirical dose calculation models, the energy dependence of the spread causes a substantial constraint. In the case of in vivo human tissues, where distribution measurements are not feasible, the problem poses a major limitation. In addition to the spread due to the currently accepted uncertainties of their I-values, a spread of the depth of the Bragg peak due to the varying compositions of soft tissues is also demonstrated, even for cases which could be considered practically identical in clinical practice. For these, the spreads found were similar to those of water or even larger, providing support to international recommendations advising that body-tissue compositions should not be given the standing of physical constants. The results show that it would be necessary to increase the margins of a clinical target volume, even in the case of a water phantom, due to an 'intrinsic basic physics uncertainty', adding to those margins usually considered in normal clinical practice due to anatomical or therapeutic strategy reasons. Individualized patient determination of tissue composition along the complete beam path, rather than CT Hounsfield numbers alone, would also probably be required even to reach 'sub-centimetre precision'.