Department of Radiation Oncology, Stanford University School of Medicine, Stanford, California.
Department of Radiation Oncology, Stanford University School of Medicine, Stanford, California; Stanford Cancer Institute, Stanford University School of Medicine, Stanford, California; Institute for Stem Cell Biology and Regenerative Medicine, Stanford University School of Medicine, Stanford, California.
Pract Radiat Oncol. 2013 Oct-Dec;3(4):294-300. doi: 10.1016/j.prro.2012.09.003. Epub 2012 Oct 24.
To determine the clinical impact of calculated dose differences between effective path length (EPL) and Monte Carlo (MC) algorithms in stereotactic ablative radiation therapy (SABR) of lung tumors.
We retrospectively analyzed the treatment plans and clinical outcomes of 77 consecutive patients treated with SABR for 82 lung tumors between 2003 and 2009 at our institution. Sixty treatments were originally planned using EPL, and 22 using MC. All plans were recalculated for the same beam specifications using MC and EPL, respectively. The doses covering 95%, 50%, and 5% (D95, D50, D5, respectively) of the target volumes were compared between EPL and MC (assumed to be the actual delivered dose), both as physical dose and biologically effective dose. Time to local recurrence was correlated with dose by Cox regression analysis. The relationship between tumor control probability (TCP) and biologically effective dose was determined via logistic regression and used to estimate the TCP decrements due to prescribing by EPL calculations.
EPL overestimated dose compared with MC in all tumor dose-volume histogram parameters in all plans. The difference was >10% of the MC D95 to the planning target volume and gross tumor volume in 60 of 82 (73%) and 52 of 82 plans (63%), respectively. Local recurrence occurred in 13 of 82 tumors. Controlling for gross tumor volume, higher physical and biologically effective planning target volume D95 correlated significantly with local control (P = .007 and P = .045, respectively). Compared with MC, prescribing based on EPL translated to a median TCP decrement of 4.3% (range, 1.2%-37%) and a >5% decrement in 46% of tumors.
Clinical follow-up for local lung tumor control in a sizable cohort of patients treated with SABR demonstrates that EPL overestimates dose by amounts that substantially decrease TCP in a large proportion. EPL algorithms should be avoided for lung tumor SABR.
确定有效路径长度（EPL）和蒙特卡罗（MC）算法之间计算剂量差异对肺肿瘤立体定向消融放疗（SABR）的临床影响。
我们回顾性分析了 2003 年至 2009 年期间在我院接受 SABR 治疗的 82 个肺肿瘤的 77 例连续患者的治疗计划和临床结果。最初有 60 例采用 EPL 计划，22 例采用 MC 计划。分别用 MC 和 EPL 为相同的射束规格重新计算所有计划。将 EPL 和 MC（假设为实际交付剂量）之间的靶区 95%、50%和 5%（D95、D50、D5）覆盖剂量进行比较，包括物理剂量和生物有效剂量。采用 Cox 回归分析将局部复发时间与剂量相关联。通过逻辑回归确定肿瘤控制概率（TCP）与生物有效剂量的关系，并用于估计因 EPL 计算而导致的 TCP 下降。
在所有计划中，EPL 与 MC 相比，在所有肿瘤剂量-体积直方图参数中都高估了剂量。在 60 个（73%）和 52 个（63%）计划中，EPL 与 MC 的计划靶区和大体肿瘤体积的 D95 差异>10%。82 个肿瘤中有 13 个发生局部复发。控制大体肿瘤体积后，较高的物理和生物有效计划靶区 D95 与局部控制显著相关（P=.007 和 P=.045）。与 MC 相比，基于 EPL 的处方导致中位 TCP 下降 4.3%（范围 1.2%-37%），46%的肿瘤 TCP 下降超过 5%。
对接受 SABR 治疗的大量肺肿瘤患者进行局部肿瘤控制的临床随访表明，EPL 高估剂量的程度会大大降低大部分肿瘤的 TCP。肺肿瘤 SABR 应避免使用 EPL 算法。
