St. Jude Children's Research Hospital, Department of Radiation Oncology, Memphis, TN, United States of America.
University of Florida Proton Therapy Institute, Department of Radiation Oncology, Jacksonville, FL, United States of America.
Phys Med Biol. 2021 Apr 1;66(7). doi: 10.1088/1361-6560/abe835.
The dosimetric advantages of proton therapy have led to its rapid proliferation in recent decades. This has been accompanied by a shift in technology from older units that deliver protons by passive scattering (PS) to newer units that increasingly use pencil-beam scanning (PBS). The biologic effectiveness of proton physical dose purportedly rises with increasing dose-weighted average linear energy transfer (LET). The objective of this study was to determine the extent to which proton delivery methods affect LET. We calculated LETfrom simple, dosimetrically matched, and clinical treatment plans with TOPAS Monte-Carlo transport code. Simple treatment plans comprised single fields of PS and PBS protons in a water phantom. We performed simulations of matched and clinical treatment plans by using the treatment and anatomic data obtained from a cohort of children with craniopharyngioma who previously received PS or PBS proton therapy. We compared the distributions of LETfrom PS and PBS delivery methods in clinically relevant ROIs. Wilcoxon signed-rank tests comparing single fields in water revealed that the LETvalues from PBS were significantly greater than those from PS inside and outside the targeted volume ( < 0.01). Statistical tests comparing LET-volume histograms from matched and clinical treatment plans showed that LETwas generally greater for PBS treatment plans than for PS treatment plans ( < 0.05). In conclusion, the proton delivery method affects LETboth inside and outside of the target volume. These findings suggest that PBS is more biologically effective than PS. Given the rapid expansion of PBS proton therapy, future studies are needed to confirm the applicability of treatment evaluation methods developed for PS proton therapy to those for modern PBS treatments to ensure their safety and effectiveness for the growing population of patients receiving proton therapy. This study uses data from two clinical trials: NCT01419067 and NCT02792582.
质子治疗的剂量学优势使其在近几十年得到了快速发展。这伴随着技术的转变，从使用被动散射（PS）输送质子的旧设备，转变为越来越多地使用铅笔束扫描（PBS）的新设备。质子物理剂量的生物效应据称随着剂量加权平均线性能量传递（LET）的增加而增加。本研究的目的是确定质子输送方法对 LET 的影响程度。我们使用 TOPAS 蒙特卡罗输运代码，从简单的、剂量匹配的和临床治疗计划中计算 LET。简单的治疗计划由水模中的 PS 和 PBS 质子单野组成。我们使用从先前接受 PS 或 PBS 质子治疗的颅咽管瘤患儿队列中获得的治疗和解剖数据，对匹配和临床治疗计划进行了模拟。我们比较了 PS 和 PBS 输送方法在临床相关 ROI 中的 LET 分布。比较水模中单野的 Wilcoxon 符号秩检验显示，PBS 的 LET 值在靶区内外均显著大于 PS（<0.01）。比较匹配和临床治疗计划的 LET 体积直方图的统计检验表明，PBS 治疗计划的 LET 通常大于 PS 治疗计划（<0.05）。总之，质子输送方法会影响靶区内外的 LET。这些发现表明，PBS 比 PS 更具有生物学效应。鉴于 PBS 质子治疗的快速发展，需要进一步的研究来确认为 PS 质子治疗开发的治疗评估方法对现代 PBS 治疗的适用性，以确保其对越来越多接受质子治疗的患者的安全性和有效性。本研究使用了两项临床试验的数据：NCT01419067 和 NCT02792582。
