Thibodeau Ryan, Li Hsin K, Tanny Sean, Gajra Ajeet, Bogart Jeffrey
Department of Radiation Oncology, State University of New York Upstate Medical University, Syracuse, USA.
Department of Radiation Oncology, University of Rochester Medical Center, Rochester, USA.
Cureus. 2021 Dec 7;13(12):e20226. doi: 10.7759/cureus.20226. eCollection 2021 Dec.
Purpose The standard radiotherapy regimen for small cell lung cancer (SCLC) was determined using dose calculations without corrections for tissue heterogeneity, while modern treatments are planned using algorithms accounting for tissue heterogeneity. We assessed differences in dose delivered using heterogeneous and homogeneous dose calculations in a cohort of patients treated for limited-stage small cell lung cancer (LS-SCLC). Methods This is a retrospective analysis of 35 patients (three-dimensional conformal radiation therapy (3D-CRT), n = 22; intensity-modulated radiation therapy (IMRT), n = 13) with LS-SCLC treated with chemoradiotherapy from 2011 to 2017. Treatment plans were developed in the Eclipse Treatment Planning System (TPS) version 13.6 using the Analytical Anisotropic Algorithm (AAA). Two plans were generated for each patient with one using the unit relative electron density and the other maintaining the same monitor units (MUs) with tissue density corrections. The prescription was 45 Gy in 30 fractions of 1.5 Gy delivered twice daily. Individuals who underwent replanning within the same treatment course were evaluated using a separate corrected and uncorrected plan sum. Variations greater than 5% in dose to the tumor or organs at risk were considered clinically relevant. A two-sided paired t-test was used to evaluate the statistical significance of the dosimetric differences. Results The percent dose difference between plans without tissue heterogeneity corrections to those with corrections resulted in an overall median difference of -3% (range: -15.1% to 9.6%; p < 0.01) for the dose covering 95% of the planning target volume (PTV D95) and was -5.6% (range: -17.3% to 5.4%; p < 0.01) for lung volume receiving ≥20 Gy (lung V20). For 3D-CRT, the median difference for the PTV D95 was -0.1% (range: -4.7% to 9.6%; p = 0.62) and the lung V20 was -4.2% (range: -9.4 to 5.4; p < 0.01). For IMRT, the median difference for the PTV D95 was -10.0% (range: -15.1% to -5.3%; p < 0.01) and the lung V20 was -8.9% (range: -17.3 to -3.5; p < 0.01). Conclusion Traditional planning without tissue heterogeneity corrections results in an overall decrease in the dose delivered to the target compared with those that incorporate tissue heterogeneity corrections. These differences are modest for 3D treatment plans but may result in clinically relevant differences for the IMRT cohort (>5% deviation).
目的 小细胞肺癌（SCLC）的标准放疗方案是在未对组织异质性进行校正的情况下进行剂量计算而确定的，而现代治疗则使用考虑组织异质性的算法进行规划。我们评估了一组接受局限期小细胞肺癌（LS-SCLC）治疗的患者中，使用异质性和均匀性剂量计算所给予剂量的差异。方法 这是一项对2011年至2017年接受放化疗的35例LS-SCLC患者（三维适形放疗（3D-CRT），n = 22；调强放疗（IMRT），n = 13）的回顾性分析。在Eclipse治疗计划系统（TPS）13.6版本中使用解析各向异性算法（AAA）制定治疗计划。为每位患者生成两个计划，一个使用单位相对电子密度，另一个在进行组织密度校正的情况下保持相同的监测单位（MU）。处方为45 Gy，分30次，每次1.5 Gy，每天照射两次。在同一治疗疗程内进行重新规划的个体，使用单独的校正和未校正计划总和进行评估。肿瘤或危及器官的剂量变化大于5%被认为具有临床相关性。使用双侧配对t检验评估剂量差异的统计学显著性。结果 未进行组织异质性校正的计划与校正后的计划之间的剂量百分比差异，对于覆盖95%计划靶体积（PTV D95）的剂量，总体中位数差异为-3%（范围：-15.1%至9.6%；p < 0.01），对于接受≥20 Gy的肺体积（肺V20）为-5.6%（范围：-17.3%至5.4%；p < 0.01）。对于3D-CRT，PTV D95的中位数差异为-0.1%（范围：-4.7%至9.6%；p = 0.62），肺V20为-4.2%（范围：-9.4至5.4；p < 0.01）。对于IMRT，PTV D95的中位数差异为-10.0%（范围：-15.1%至-5.3%；p < 0.01），肺V20为-8.9%（范围：-17.3至-3.5；p < 0.01）。结论 与纳入组织异质性校正的计划相比，未进行组织异质性校正的传统计划导致给予靶区的剂量总体降低。这些差异在3D治疗计划中较小，但可能导致IMRT队列出现临床相关差异（偏差>5%）。
