Aims

Exposure of the heart to radiation increases the risk of ischaemic heart disease, proportionate to the mean heart dose (MHD). Radiotherapy techniques including proton beam therapy (PBT) can reduce MHD. The aims of this study were to quantify the MHD reduction achievable by PBT compared with volumetric modulated arc therapy in breath hold (VMAT-BH) in patients with pectus excavatum (PEx), to identify an anatomical metric from a computed tomography scan that might indicate which patients will achieve the greatest MHD reductions from PBT.

Materials and methods

Sixteen patients with PEx (Haller Index ≥2.7) were identified from radiotherapy planning computed tomography images. Left breast/chest wall, axilla (I–IV) and internal mammary node (IMN) volumes were delineated. VMAT and PBT plans were prepared, all satisfying target coverage constraints. Signed-rank comparisons of techniques were undertaken for the mean dose to the heart, ipsilateral lung and contralateral breast. Spearman's rho correlations were calculated for anatomical metrics against MHD reduction achieved by PBT.

Results

The mean MHD for VMAT-BH plans was 4.1 Gy compared with 0.7 Gy for PBT plans. PBT reduced MHD by an average of 3.4 Gy (range 2.8–4.4 Gy) compared with VMAT-BH (P < 0.001). PBT significantly reduced the mean dose to the ipsilateral lung (4.7 Gy, P < 0.001) and contralateral breast (2.7 Gy, P < 0.001). The distance (mm) at the most inferomedial extent of IMN volume (IMN to heart distance) negatively correlated with MHD reduction achieved by PBT (Spearman's rho –0.88 (95% confidence interval –0.96 to –0.67, P < 0.001)).

Conclusion

For patients with PEx requiring left-sided breast and IMN radiotherapy, a clinically significant MHD reduction is achievable using PBT, compared with the optimal photon technique (VMAT-BH). This is a patient group in whom PBT could have the greatest benefit.

中文翻译：

---

质子束治疗对于需要左乳、腋窝和内乳淋巴结放疗的漏斗胸患者有何帮助？

 目标

心脏暴露于辐射会增加患缺血性心脏病的风险，与平均心脏剂量（MHD）成正比。包括质子束治疗 (PBT) 在内的放射治疗技术可以降低 MHD。本研究的目的是量化漏斗胸 (PEx) 患者中 PBT 与屏气容积调制弧形疗法 (VMAT-BH) 相比可实现的 MHD 减少，从计算机断层扫描中确定可能表明以下情况的解剖学指标：哪些患者将通过 PBT 实现最大的 MHD 降低。

 材料和方法

从放疗计划计算机断层扫描图像中识别出 16 名 PEx 患者（Haller 指数≥2.7）。描绘出左乳房/胸壁、腋窝 (I–IV) 和内乳淋巴结 (IMN) 体积。 VMAT 和 PBT 计划均已制定，均满足目标覆盖限制。对心脏、同侧肺和对侧乳房的平均剂量进行技术的符号等级比较。计算了 Spearman 的 rho 相关性，用于针对 PBT 实现的 MHD 降低的解剖学指标。

 结果

VMAT-BH 计划的平均 MHD 为 4.1 Gy，而 PBT 计划的平均 MHD 为 0.7 Gy。与 VMAT-BH 相比，PBT 平均使 MHD 降低 3.4 Gy（范围 2.8-4.4 Gy）（ P < 0.001）。 PBT显着降低了同侧肺部（4.7 Gy， P < 0.001）和对侧乳房（2.7 Gy， P < 0.001）的平均剂量。 IMN 体积最内侧范围的距离 (mm)（IMN 到心脏的距离）与 PBT 实现的 MHD 降低呈负相关（Spearman's rho –0.88（95% 置信区间 –0.96 至 –0.67， P < 0.001））。

 结论

对于需要左侧乳房和 IMN 放疗的 PEx 患者，与最佳光子技术 (VMAT-BH) 相比，使用 PBT 可以实现临床上显着的 MHD 降低。这是 PBT 能够获得最大益处的患者群体。