Lebel-Cormier Marie-Anne, Boilard Tommy, Bernier Martin, Beaulieu Luc
Centre Intégré de cancérologie and Axe Oncologie du CRCHU de Québec - Université Laval, CHU de Québec - Université Laval, Québec, Canada.
Centre de recherche sur le cancer, Université Laval, Québec, Canada.
Med Phys. 2024 May;51(5):3758-3765. doi: 10.1002/mp.16955. Epub 2024 Jan 31.
The interest of using fiber Bragg gratings (FBGs) dosimeters in radiotherapy (RT) lies in their (i) microliter detection volume, (ii) customizable spatial resolution, (iii) multi-point dose measurement, (iv) real-time data acquisition and (v) insensitivity to Cherenkov light. These characteristics could prove very useful for characterizing dose distributions of small and nonstandard fields with high spatial resolution.
We developed a multi-point FBGs dosimeter customized for small field RT dosimetry with a spatial resolution of 1 mm.
The 3 cm-long multi-point dosimeter is made by embedding a 80 silica fiber containing an array of thirty (30) co-located 1 mm-long fs-written FBGs inside a plastic cylinder with an UV curing optical adhesive. With its higher thermal expansion coefficient, the plastic cylinder increases the sensitivity of the dosimeter by stretching the fiber containing the FBGs when the temperature rises slightly due to radiation energy deposition. Irradiations (2000 MU at 600 MU/min) were performed with a Varian TrueBeam linear accelerator.
The dose profile of a 2 2 cm 6 MV beam was measured with a mean relative difference of 1.8% (excluding the penumbra region). The measured output factors for a 6 MV beam are in general agreement with the expected values within the experimental uncertainty (except for the 2 2 cm field). The detector response to different energy of photon and electron beams is within 5% of the mean response ( pm/Gy). The calorimeter's post-irradiation thermal decay is in agreement with the theory.
An energy-independent small field calorimeter that allows dose profile and output factor measurements for RT using FBGs was developed, which, to our knowledge, has never been done before. This type of detector could prove really useful for small field dosimetry, but also potentially for MRI-LINAC since FBGs are insensitive to magnetic fields and for FLASH since FBGs have been used to measure doses up to 100 kGy.
在放射治疗（RT）中使用光纤布拉格光栅（FBG）剂量计的优势在于其（i）微升检测体积，（ii）可定制的空间分辨率，（iii）多点剂量测量，（iv）实时数据采集以及（v）对切伦科夫光不敏感。这些特性对于以高空间分辨率表征小尺寸和非标准射野的剂量分布可能非常有用。
我们开发了一种专为小射野RT剂量测定定制的多点FBG剂量计，其空间分辨率为1毫米。
通过将一根3厘米长的多点剂量计制作而成，该剂量计是将一根包含三十（30）个共定位的1毫米长飞秒写入FBG阵列的80微米石英光纤，用紫外光固化光学粘合剂嵌入到一个塑料圆柱体内。由于塑料圆柱体具有较高的热膨胀系数，当由于辐射能量沉积导致温度略有升高时，它会通过拉伸包含FBG的光纤来提高剂量计的灵敏度。使用瓦里安TrueBeam直线加速器进行照射（600 MU/分钟，共2000 MU）。
测量了一个2×2厘米、6兆伏射束的剂量分布，平均相对差异为1.8%（不包括半影区）。对于6兆伏射束测量得到的输出因子在实验不确定度范围内与预期值总体一致（2×2厘米射野除外）。探测器对不同能量的光子束和电子束的响应在平均响应的5%以内（±pm/Gy）。量热计辐照后的热衰减与理论相符。
开发了一种与能量无关的小射野量热计，它能够使用FBG进行RT的剂量分布和输出因子测量，据我们所知，此前从未有过此类研究。这种类型的探测器对于小射野剂量测定可能非常有用，而且由于FBG对磁场不敏感，对于磁共振直线加速器（MRI-LINAC）以及由于FBG已被用于测量高达100千戈瑞的剂量，对于FLASH放疗也可能具有潜在用途。
