Bizzocchi Nicola, Fracchiolla Francesco, Schwarz Marco, Algranati Carlo
Azienda Provinciale per i Servizi Sanitari (APSS) Protontherapy Department, Trento, Italy.
Azienda Provinciale per i Servizi Sanitari (APSS) Protontherapy Department, Trento, Italy.
Med Dosim. 2017;42(3):238-246. doi: 10.1016/j.meddos.2017.05.001. Epub 2017 Jun 20.
In a radiotherapy center, daily quality assurance (QA) measurements are performed to ensure that the equipment can be safely used for patient treatment on that day. In a pencil beam scanning (PBS) proton therapy center, spot positioning, spot size, range, and dose output are usually verified every day before treatments. We designed, built, and tested a new, reliable, sensitive, and inexpensive phantom, coupled with an array of ionization chambers, for daily QA that reduces the execution times while preserving the reliability of the test. The phantom is provided with 2 pairs of wedges to sample the Bragg peak at different depths to have a transposition on the transverse plane of the depth dose. Three "boxes" are used to check spot positioning and delivered dose. The box thickness helps spread the single spot and to fit a Gaussian profile on a low resolution detector. We tested whether our new QA solution could detect errors larger than our action levels: 1 mm in spot positioning, 2 mm in range, and 10% in spot size. Execution time was also investigated. Our method is able to correctly detect 98% of spots that are actually in tolerance for spot positioning and 99% of spots out of 1 mm tolerance. All range variations greater than the threshold (2 mm) were correctly detected. The analysis performed over 1 month showed a very good repeatability of spot characteristics. The time taken to perform the daily quality assurance is 20 minutes, a half of the execution time of the former multidevice procedure. This "in-house build" phantom substitutes 2 very expensive detectors (a multilayer ionization chamber [MLIC] and a strip chamber, reducing by 5 times the cost of the equipment. We designed, built, and validated a phantom that allows for accurate, sensitive, fast, and inexpensive daily QA procedures in proton therapy with PBS.
在放射治疗中心，每天都会进行质量保证（QA）测量，以确保当天设备可安全用于患者治疗。在笔形束扫描（PBS）质子治疗中心，通常在每天治疗前对束斑定位、束斑大小、射程和剂量输出进行验证。我们设计、制造并测试了一种新型、可靠、灵敏且廉价的模体，它与一系列电离室相结合，用于每日QA，在保持测试可靠性的同时减少了执行时间。该模体配有两对楔形物，用于在不同深度对布拉格峰进行采样，以便在深度剂量的横截面上进行转换。三个“盒体”用于检查束斑定位和输送剂量。盒体厚度有助于扩展单个束斑，并在低分辨率探测器上拟合高斯分布。我们测试了我们的新QA解决方案是否能够检测出大于我们行动水平的误差：束斑定位误差1毫米、射程误差2毫米和束斑大小误差10%。还对执行时间进行了研究。我们的方法能够正确检测出98%实际处于束斑定位公差范围内的束斑以及99%超出1毫米公差的束斑。所有大于阈值（2毫米）的射程变化均被正确检测到。在1个月内进行的分析显示束斑特性具有非常好的重复性。进行每日质量保证所需的时间为20分钟，是之前多设备程序执行时间的一半。这种“内部制造”的模体替代了2个非常昂贵的探测器（一个多层电离室[MLIC]和一个条带室），使设备成本降低了5倍。我们设计、制造并验证了一种模体，它能够在PBS质子治疗中实现准确、灵敏、快速且廉价的每日QA程序。
