Proton beams are widely used worldwide to treat localized tumours, the lower entrance dose and no exit dose, thus sparing surrounding normal tissues, being the main advantage of this treatment modality compared to conventional photon techniques. Clinical proton beam therapy treatment planning is based on the use of a general relative biological effectiveness (RBE) of 1.1 along the whole beam penetration depth, without taking into account the documented increase in RBE at the end of the depth dose profile, in the Bragg peak and beyond. However, an inaccurate estimation of the RBE can cause both underdose or overdose, in particular it can cause the unfavourable situation of underdosing the tumour and overdosing the normal tissue just beyond the tumour, which limits the treatment success and increases the risk of complications. In view of a more precise dose delivery that takes into account the variation of RBE, experimental microdosimetry offers valuable tools for the quality assurance of LET or RBE-based treatment planning systems. The purpose of this work is to compare the response of two different microdosimetry systems: the mini-TEPC and the MicroPlus-Bridge detector. Microdosimetric spectra were measured across the 62 MeV spread out Bragg peak of CATANA with the mini-TEPC and with the Bridge microdosimeter. The frequency and dose distributions of lineal energy were compared and the different contributions to the spectra were analysed, discussing the effects of different site sizes and chord length distributions. The shape of the lineal energy distributions measured with the two detectors are markedly different, due to the different water-equivalent sizes of the sensitive volumes: 0.85 μm for the TEPC and 17.3 μm for the silicon detector. When the Loncol’s biological weighting function is applied to calculate the microdosimetric assessment of the RBE, both detectors lead to results that are consistent with biological survival data for glioma U87 cells. Both the mini-TEPC and the MicroPlus-Bridge detector can be used to assess the RBE variation of a 62 MeV modulated proton beam along its penetration depth. The microdosimetric assessment of the RBE based on the Loncol’s weighting function is in good agreement with radiobiological results when the 10% biological uncertainty is taken into account.

质子束在世界范围内被广泛用于治疗局部肿瘤，较低的入口剂量和无出口剂量，因此可以保护周围的正常组织，这是这种治疗方式与传统光子技术相比的主要优势。临床质子束治疗治疗计划基于沿整个射束穿透深度使用 1.1 的一般相对生物有效性 (RBE)，而没有考虑在 Bragg 中记录的深度剂量分布结束时 RBE 的增加高峰及以后。然而，对RBE的不准确估计可能导致剂量不足或过量，特别是它可能导致肿瘤剂量不足和肿瘤外正常组织过量的不利情况，这限制了治疗成功并增加了并发症的风险。鉴于考虑到 RBE 变化的更精确的剂量输送，实验性微剂量学为 LET 或基于 RBE 的治疗计划系统的质量保证提供了有价值的工具。这项工作的目的是比较两种不同的微剂量系统的响应：mini-TEPC 和 MicroPlus-Bridge 检测器。用 mini-TEPC 和 Bridge 微剂量计在 CATANA 的 62 MeV 展开的布拉格峰上测量微剂量光谱。比较了线性能量的频率和剂量分布，分析了对光谱的不同贡献，讨论了不同位点大小和弦长分布的影响。用两个探测器测量的线性能量分布的形状明显不同，由于敏感体积的水当量大小不同：TEPC 为 0.85 μm，硅检测器为 17.3 μm。当应用 Loncol 的生物加权函数来计算 RBE 的微剂量评估时，两种检测器的结果都与胶质瘤 U87 细胞的生物存活数据一致。mini-TEPC 和 MicroPlus-Bridge 探测器均可用于评估 62 MeV 调制质子束沿其穿透深度的 RBE 变化。当考虑到 10% 的生物不确定性时，基于 Loncol 加权函数的 RBE 的微剂量评估与放射生物学结果非常吻合。当应用 Loncol 的生物加权函数来计算 RBE 的微剂量评估时，两种检测器的结果都与胶质瘤 U87 细胞的生物存活数据一致。mini-TEPC 和 MicroPlus-Bridge 探测器均可用于评估 62 MeV 调制质子束沿其穿透深度的 RBE 变化。当考虑到 10% 的生物不确定性时，基于 Loncol 加权函数的 RBE 的微剂量评估与放射生物学结果非常吻合。当应用 Loncol 的生物加权函数来计算 RBE 的微剂量评估时，两种检测器的结果都与胶质瘤 U87 细胞的生物存活数据一致。mini-TEPC 和 MicroPlus-Bridge 探测器均可用于评估 62 MeV 调制质子束沿其穿透深度的 RBE 变化。当考虑到 10% 的生物不确定性时，基于 Loncol 加权函数的 RBE 的微剂量评估与放射生物学结果非常吻合。