The European Synchrotron Radiation Facility, ID17 Biomedical Beamline, Grenoble, France; Inserm UA7 STROBE, Grenoble Alpes University, Grenoble, France; Swansea University Medical School, Singleton Park, Swansea SA2 8PP, United Kingdom.
Helmholtz-Centre Munich, Institute of Innovative Radiation Therapy, Munich, Germany; Klinikum rechts der Isar, Department for Radiation Oncology, Technical University of Munich, Germany.
Phys Med. 2019 Sep;65:106-113. doi: 10.1016/j.ejmp.2019.08.012. Epub 2019 Aug 23.
Microbeam radiation therapy is a developing technique that promises superior tumour control and better normal tissue tolerance using spatially fractionated X-ray beams only tens of micrometres wide. Radiochromic film dosimetry at micrometric scale was performed using a microdensitometer, but this instrument presents limitations in accuracy and precision, therefore the use of a microscope is suggested as alternative. The detailed procedures developed to use the two devices are reported allowing a comparison.
Films were irradiated with single microbeams and with arrays of 50 µm wide microbeams spaced by a 400 µm pitch, using a polychromatic beam with mean energy of 100 keV. The film dose measurements were performed using two independent instruments: a microdensitometer (MDM) and an optical microscope (OM).
The mean values of the absolute dose measured with the two instruments differ by less than 5% but the OM provides reproducibility with a standard deviation of 1.2% compared to up to 7% for the MDM. The resolution of the OM was determined to be ~ 1 to 2 µm in both planar directions able to resolve pencil beams irradiation, while the MDM reaches at the best 20 µm resolution along scanning direction. The uncertainties related to the data acquisition are 2.5-3% for the OM and 9-15% for the MDM.
The comparison between the two devices validates that the OM provides equivalent results to the MDM with better precision, reproducibility and resolution. In addition, the possibility to study dose distributions in two-dimensions over wider areas definitely sanctions the OM as substitute of the MDM.
微束放射治疗是一种发展中的技术，它使用只有数十微米宽的空间分割 X 射线束，有望实现更好的肿瘤控制和更好的正常组织耐受。使用微光度计进行了微观尺度的放射色胶片剂量测定，但该仪器在准确性和精密度方面存在局限性，因此建议使用显微镜作为替代方法。报告了开发用于这两种设备的详细程序，允许进行比较。
使用多色光束，用平均能量为 100keV 的光束对单微束和间隔 400µm 的 50µm 宽微束阵列进行辐照。使用两种独立的仪器进行胶片剂量测量：微光度计（MDM）和光学显微镜（OM）。
两种仪器测量的绝对剂量平均值相差小于 5%，但 OM 提供的重复性标准偏差为 1.2%，而 MDM 可达 7%。OM 的分辨率在两个平面方向上均确定为~1 至 2µm，能够分辨铅笔束照射，而 MDM 在最佳情况下沿扫描方向达到 20µm 的分辨率。与数据采集相关的不确定度为 OM 的 2.5-3%，MDM 的 9-15%。
两种设备的比较验证了 OM 可提供与 MDM 相当的结果，具有更好的精度、重复性和分辨率。此外，在更广泛的区域内研究二维剂量分布的可能性肯定使 OM 成为 MDM 的替代品。
