Graduate School of Biomedical Science and Engineering, Hokkaido University, Sapporo, Japan.
Faculty of Engineering, Hokkaido University, Sapporo, Japan.
Med Phys. 2022 Jan;49(1):702-713. doi: 10.1002/mp.15367. Epub 2021 Dec 7.
In the scanning beam delivery of protons, different portions of the target are irradiated with different linear energy transfer protons with various time intervals and irradiation times. This research aimed to evaluate the spatially dependent biological effectiveness of protracted irradiation in scanning proton therapy.
One and two parallel opposed fields plans were created in water phantom with the prescribed dose of 2 Gy. Three scenarios (instantaneous, continuous, and layered scans) were used with the corresponding beam delivery models. The biological dose (physical dose × relative biological effectiveness) was calculated using the linear quadratic model and the theory of dual radiation action to quantitatively evaluate the dose delivery time effect. In addition, simulations using clinical plans (postoperative seminoma and prostate tumor cases) were conducted to assess the impact of the effects on the dose volume histogram parameters and homogeneity coefficient (HC) in targets.
In a single-field plan of water phantom, when the treatment time was 19 min, the layered-scan scenario showed a decrease of <0.2% (almost 3.3%) in the biological dose from the plan on the distal (proximal) side because of the high (low) dose rate. This is in contrast to the continuous scenario, where the biological dose was almost uniformly decreased over the target by approximately 3.3%. The simulation with clinical geometry showed that the decrease rates in D were 0.9% and 1.5% for every 10 min of treatment time prolongation for postoperative seminoma and prostate tumor cases, respectively, whereas the increase rates in HC were 0.7% and 0.2%.
In protracted irradiation in scanning proton therapy, the spatially dependent dose delivery time structure in scanning beam delivery can be an important factor for accurate evaluation of biological effectiveness.
在质子扫描束传输中，通过不同的时间间隔和照射时间，用不同线性传能密度的质子照射靶的不同部位。本研究旨在评估扫描质子治疗中迁延照射的空间依赖性生物效应。
在水模体中创建了一个和两个平行对置野的计划，规定剂量为 2 Gy。使用三种情况（瞬时、连续和分层扫描）和相应的束流传输模型。使用线性二次模型和双辐射作用理论计算生物剂量（物理剂量×相对生物效应），定量评估剂量传递时间效应。此外，还对临床计划（术后精原细胞瘤和前列腺肿瘤病例）进行了模拟，以评估对靶区剂量体积直方图参数和均匀性系数（HC）的影响。
在水模体的单野计划中，当治疗时间为 19 分钟时，由于高（低）剂量率，分层扫描方案在远端（近端）侧的计划中，生物剂量下降了<0.2%（几乎 3.3%）。这与连续扫描方案形成对比，其中靶区的生物剂量几乎均匀下降了约 3.3%。临床几何形状的模拟显示，对于术后精原细胞瘤和前列腺肿瘤病例，每延长 10 分钟治疗时间，D 下降率分别为 0.9%和 1.5%，而 HC 上升率分别为 0.7%和 0.2%。
在扫描质子治疗中的迁延照射中，扫描束传输中空间依赖性剂量传递时间结构可能是准确评估生物效应的一个重要因素。
