Department of Radiation Oncology, Henry Ford Hospital, Detroit, USA.
Radiother Oncol. 2013 Dec;109(3):498-504. doi: 10.1016/j.radonc.2013.10.012. Epub 2013 Nov 11.
To retrospectively compute dose distributions for lung cancer patients treated with SABR, and to correlate dose distributions with outcome using a tumor control probability (TCP) model.
Treatment plans for 133 NSCLC patients treated using 12 Gy/fxn × 4 (BED=106 Gy), and planned using a pencil-beam (1D-equivalent-path-length, EPL-1D) algorithm were retrospectively re-calculated using model-based algorithms (including convolution/superposition, Monte Carlo). 4D imaging was performed to manage motion. TCP was computed using the Marsden model and associations between dose and outcome were inferred.
Mean D95 reductions of 20% (max.=33%) were noted with model-based algorithms (relative to EPL-1D) for the smallest tumors (PTV<20 cm(3)), corresponding to actual delivered D95 BEDs of ≈ 60-85 Gy. For larger tumors (PTV>100 cm(3)), D95 reductions were ≈ 10% (BED>100 Gy). Mean lung doses (MLDs) were 15% lower for model-based algorithms for PTVs<20 cm(3). No correlation between tumor size and 2-year local control rate was observed clinically, consistent with TCP calculations, both of which were ≈ 90% across all PTV bins.
Results suggest that similar control rates might be achieved for smaller tumors using lower BEDs relative to larger tumors. However, more studies with larger patient cohorts are necessary to confirm this possible finding.
回顾性计算立体定向消融放疗（SABR）治疗肺癌患者的剂量分布，并使用肿瘤控制概率（TCP）模型将剂量分布与结果相关联。
对 133 例接受 12 Gy/fxn × 4（BED=106 Gy）治疗的非小细胞肺癌患者的治疗计划进行回顾性重新计算，使用基于模型的算法（包括卷积/叠加、蒙特卡罗）对其进行计划。采用 4D 成像技术进行运动管理。使用 Marsden 模型计算 TCP，并推断剂量与结果之间的关联。
对于最小的肿瘤（PTV<20 cm³），与基于模型的算法（相对于 EPL-1D）相比，平均 D95 降低了 20%（最大降低 33%），这对应于实际交付的 D95 BED 约为 60-85 Gy。对于较大的肿瘤（PTV>100 cm³），D95 降低约 10%（BED>100 Gy）。对于 PTV<20 cm³ 的肿瘤，基于模型的算法的平均肺剂量（MLD）降低了 15%。在临床观察中，肿瘤大小与 2 年局部控制率之间没有相关性，这与 TCP 计算结果一致，所有 PTV bins 的控制率均约为 90%。
结果表明，对于较小的肿瘤，使用较低的 BED 可能会获得与较大的肿瘤相似的控制率。然而，需要更多的大型患者队列研究来证实这一可能的发现。
