Patrick G. Johnston Centre for Cancer Research, Queen's University Belfast, Belfast BT9 7AE, United Kingdom.
Department of Radiotherapy Medical Physics, Northern Ireland Cancer Centre Belfast Health and Social Care Trust, Belfast BT9 7AB, United Kingdom.
Phys Med Biol. 2024 Oct 18;69(21). doi: 10.1088/1361-6560/ad84b7.
. Optical fibre dosimeters (OFDs) offer great promise for real-timedose measurement in radiation-based treatment modalities such as radiotherapy and brachytherapy. This is attributed to their many useful qualities such as high spatial resolution and sensitivity. However, there are several requirements that an optical fibre dosimeter must meet to be acceptable for dose measurement in a specified treatment modality. In this work, the dosimetric performance of a novel optical fibre dosimeter for use in external beam radiotherapy is presented.. The dosimeter was characterised for photon beam energies between 6-15 MV using a Varian TrueBeam Linac at dose rates between 100-2400 MU/min and assessed based on its repeatability, dose dependence, dose rate dependence, energy dependence and dose-per-pulse dependence.. The results demonstrated excellent short-term repeatability of 0.3%, good linearity in response (R2>0.9997), and minor dose rate dependence between 0.53%-2.49% for all beam qualities investigated. As the scintillator of the OFD is non-water equivalent, Monte-Carlo-TOPAS simulations were used to calculate the absorbed dose energy dependence. A dose-per-pulse dependence was also investigated and compared with dosimetry measurements made with an ionisation chamber and simulated from the treatment planning system. An over-response of 20%was found at the lowest investigated dose-per-pulse, and an under-response of 34%was found at the highest investigated dose-per-pulse. This is believed to be due to an intrinsic energy dependence making this type of OFD unsuitable for external beam radiotherapy dosimetry.. The OFD evaluated in this work was primarily designed for high-dose-rate brachytherapy whereas this study includes the first measurements made in external beam radiotherapy and highlights the challenges of transferability of the dosimeter to a different radiation source.
光纤剂量计（OFD）在放射治疗和近距离治疗等基于辐射的治疗方式中提供了实时剂量测量的巨大潜力。这归因于它们许多有用的特性，如高空间分辨率和灵敏度。然而，对于在特定治疗方式中进行剂量测量而言，光纤剂量计需要满足几个要求。在这项工作中，展示了一种新型光纤剂量计在外部束放射治疗中的剂量学性能。该剂量计在光子束能量为 6-15 MeV 之间进行了特性描述，使用的是瓦里安 TrueBeam 直线加速器，剂量率在 100-2400 MU/min 之间，并根据其重复性、剂量依赖性、剂量率依赖性、能量依赖性和剂量脉冲依赖性进行了评估。结果表明，在所有研究的光束质量下，该剂量计具有出色的短期重复性（0.3%）、响应（R2>0.9997）的良好线性度，以及较小的剂量率依赖性（0.53%-2.49%）。由于 OFD 的闪烁体是非水等效的，因此使用蒙特卡罗- TOPAS 模拟来计算吸收剂量的能量依赖性。还研究了剂量脉冲依赖性，并与使用电离室进行的剂量测量和从治疗计划系统模拟进行了比较。在研究的最低剂量脉冲下，发现响应过度了 20%，在研究的最高剂量脉冲下，发现响应不足了 34%。这被认为是由于内在的能量依赖性，使得这种类型的 OFD 不适合外部束放射治疗剂量测量。在这项工作中评估的 OFD 主要设计用于高剂量率近距离治疗，而这项研究包括在外部束放射治疗中的首次测量，并强调了将剂量计转移到不同辐射源的挑战性。
