Department of Radiation Oncology, University of Florida, and University of Florida Health Proton Therapy Institute, Jacksonville, FL, USA.
J Appl Clin Med Phys. 2019 Oct;20(10):67-73. doi: 10.1002/acm2.12714. Epub 2019 Sep 3.
To investigate the dosimetric impact of prostate intrafraction motion on proton double-scattering (DS) and uniform scanning (US) treatments using electromagnetic transponder-based prostate tracking data in simulated treatment deliveries.
In proton DS delivery, the spread-out Bragg peak (SOBP) is created almost instantaneously by the constant rotation of the range modulator. US, however, delivers each entire energy layer of the SOBP sequentially from distal to proximal direction in time, which can interplay with prostate intrafraction motion. This spatiotemporal interplay during proton treatment was simulated to evaluate its dosimetric impact. Prostate clinical target volume (CTV) dose was obtained by moving CTV through dose matrices of the energy layers according to prostate-motion traces. Fourteen prostate intrafraction motion traces of each of 17 prostate patients were used in the simulated treatment deliveries. Both single fraction dose-volume histograms (DVHs) and fraction-cumulative DVHs were obtained for both 2 Gy per fraction and 7.25 Gy per fraction stereotactic body radiotherapy (SBRT).
The simulation results indicated that CTV dose degradation depends on the magnitude and direction of prostate intrafraction motion and is patient specific. For some individual fractions, prescription dose coverage decreased in both US and DS treatments, and hot and cold spots inside the CTV were observed in the US results. However, fraction-cumulative CTV dose coverage showed much reduced dose degradation for both DS and US treatments for both 2 Gy per fraction and SBRT simulations.
This study indicated that CTV dose inhomogeneity may exist for some patients with severe prostate intrafraction motion during US treatments. However, there are no statistically significant dose differences between DS and US treatment simulations. Cumulative dose of multiple-fractions significantly reduced dose uncertainties.
利用基于电磁转发器的前列腺追踪数据，研究质子双散射（DS）和均匀扫描（US）治疗中前列腺内部分运动对剂量的影响。
在质子 DS 治疗中，扩展布拉格峰（SOBP）通过不断旋转调强器即时产生。然而，US 则是从远到近的顺序逐次输送 SOBP 的整个能量层，这可能会与前列腺内部分运动相互作用。本研究模拟质子治疗期间的这种时空相互作用，以评估其对剂量的影响。通过根据前列腺运动轨迹将 CTV 移动到能量层的剂量矩阵中，获得前列腺临床靶区（CTV）剂量。17 例前列腺患者的每个患者的 14 个前列腺内部分运动轨迹都用于模拟治疗。对 2 Gy 单次分割和 7.25 Gy 单次分割立体定向体部放疗（SBRT），都获得了单部分剂量-体积直方图（DVH）和部分累积剂量-DVH。
模拟结果表明，CTV 剂量的降低取决于前列腺内部分运动的幅度和方向，并且是患者特异性的。对于某些个别部分，US 和 DS 治疗中处方剂量的覆盖度都降低了，并且在 US 结果中观察到 CTV 内的热点和冷点。然而，对于 2 Gy 单次分割和 SBRT 模拟，DS 和 US 治疗的部分累积 CTV 剂量覆盖率都显示出剂量降低的程度明显降低。
本研究表明，对于一些前列腺内部分运动剧烈的患者，US 治疗期间可能存在 CTV 剂量不均匀性。然而，DS 和 US 治疗模拟之间没有统计学显著的剂量差异。多次分割的累积剂量显著降低了剂量的不确定性。
