Sammer Matthias, Rousseti Aikaterini, Girst Stefanie, Reindl Judith, Dollinger Günther
Faculty of Aerospace Engineering, Institute of Applied Physics and Measurement Technology (LRT 2), Universität der Bundeswehr München, D-85577 Neubiberg, Germany.
Cancers (Basel). 2022 Oct 21;14(20):5162. doi: 10.3390/cancers14205162.
The prerequisite of any radiation therapy modality (X-ray, electron, proton, and heavy ion) is meant to meet at least a minimum prescribed dose at any location in the tumor for the best tumor control. In addition, there is also an upper dose limit within the tumor according to the International Commission on Radiation Units (ICRU) recommendations in order to spare healthy tissue as well as possible. However, healthy tissue may profit from the lower side effects when waving this upper dose limit and allowing a larger heterogeneous dose deposition in the tumor, but maintaining the prescribed minimum dose level, particularly in proton minibeam therapy. Methods: Three different longitudinally heterogeneous proton irradiation modes and a standard spread-out Bragg peak (SOBP) irradiation mode are simulated for their depth-dose curves under the constraint of maintaining a minimum prescribed dose anywhere in the tumor region. Symmetric dose distributions of two opposing directions are overlaid in a 25 cm-thick water phantom containing a 5 cm-thick tumor region. Interlaced planar minibeam dose distributions are compared to those of a broadbeam using the same longitudinal dose profiles. Results and Conclusion: All longitudinally heterogeneous proton irradiation modes show a dose reduction in the healthy tissue compared to the common SOBP mode in the case of broad proton beams. The proton minibeam cases show eventually a much larger mean cell survival and thus a further reduced equivalent uniform dose (EUD) in the healthy tissue than any broadbeam case. In fact, the irradiation mode using only one proton energy from each side shows better sparing capabilities in the healthy tissue than the common spread-out Bragg peak irradiation mode with the option of a better dose fall-off at the tumor edges and an easier technical realization, particularly in view of proton minibeam irradiation at ultra-high dose rates larger than ~10 Gy/s (so-called FLASH irradiation modes).
任何放射治疗方式（X射线、电子、质子和重离子）的前提都是要在肿瘤的任何位置至少达到规定的最小剂量，以实现最佳的肿瘤控制。此外，根据国际辐射单位委员会（ICRU）的建议，肿瘤内还有一个剂量上限，以便尽可能保护健康组织。然而，当放宽这个剂量上限并允许在肿瘤内有更大的非均匀剂量沉积，但保持规定的最小剂量水平时，健康组织可能会因副作用较小而受益，特别是在质子微束治疗中。方法：模拟三种不同的纵向非均匀质子照射模式和一种标准的扩展布拉格峰（SOBP）照射模式在肿瘤区域任何位置保持规定最小剂量约束下的深度剂量曲线。在一个包含5厘米厚肿瘤区域的25厘米厚水模体中叠加两个相反方向的对称剂量分布。将交错平面微束剂量分布与使用相同纵向剂量分布的宽束剂量分布进行比较。结果与结论：在宽质子束的情况下，与普通的SOBP模式相比，所有纵向非均匀质子照射模式在健康组织中的剂量都有所降低。质子微束情况最终显示出比任何宽束情况更大的平均细胞存活率，因此健康组织中的等效均匀剂量（EUD）进一步降低。事实上，从两侧仅使用一种质子能量的照射模式在健康组织中显示出比普通的扩展布拉格峰照射模式更好的保护能力，在肿瘤边缘有更好的剂量下降，并且技术实现更容易，特别是考虑到大于~10 Gy/s的超高剂量率下的质子微束照射（所谓的FLASH照射模式）。
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