Mancosu Pietro, Pasquino Massimo, Reggiori Giacomo, Masi Laura, Russo Serenella, Stasi Michele
Medical Physics Unit of Radiation Oncology Dept., Humanitas Research Hospital, Milano, Italy.
A.O. Ordine Mauriziano di Torino, Torino, Italy.
Phys Med. 2017 Sep;41:33-38. doi: 10.1016/j.ejmp.2017.03.024. Epub 2017 Apr 3.
In modern radiation therapy accurate small fields dosimetry is a challenge and its standardization is fundamental to harmonize delivered dose in different institutions. This study presents a multicenter characterization of MLC-defined small field for Elekta and Varian linear accelerators. Measurements were performed using the Exradin W1 plastic scintillator detector.
The project enrolled 24 Italian centers. Each center performed Tissue Phantom Ratio (TPR), in-plane and cross-plane dose profiles of 0.8×0.8cm field, and Output Factor (OF) measurements for square field sizes ranging from 0.8 to 10cm. Set-up conditions were 10cm depth in water phantom at SSD 90cm. Measurements were performed using two twin Exradin W1 plastic scintillator detectors (PSD) correcting for the Cerenkov effect as proposed by the manufacturer.
Data analysis from 12 Varian and 12 Elekta centers was performed. Measurements of 7 centers were not included due to cable problems. TPR measurements showed standard deviations (SD)<1%; SD<0.4mm for the profile penumbra was obtained, while FWHM measurements showed SD<0.5mm. OF measurements showed SD<1.5% for field size greater than 2×2cm. Median OFs values were in agreement with the recent bibliography.
High degree of consistency was registered for all the considered parameters. This work confirmed the importance of multicenter dosimetric intercomparison. W1 PSD could be considered as a good candidate for small field measurements.
在现代放射治疗中，精确的小射野剂量测定是一项挑战，其标准化对于不同机构中所给予剂量的统一至关重要。本研究展示了针对医科达和瓦里安直线加速器的多叶准直器定义的小射野的多中心特性描述。测量使用Exradin W1塑料闪烁探测器进行。
该项目纳入了24个意大利中心。每个中心进行了组织体模比（TPR）、0.8×0.8cm射野的平面内和平面交叉剂量分布以及0.8至10cm方形射野尺寸的输出因子（OF）测量。设置条件为在水模中90cm源皮距下10cm深度处。测量使用两个成对的Exradin W1塑料闪烁探测器（PSD），按照制造商建议对切伦科夫效应进行校正。
对来自12个瓦里安中心和12个医科达中心的数据进行了分析。由于电缆问题，7个中心的测量数据未被纳入。TPR测量显示标准差（SD）<1%；射野半值层测量得到的标准差<0.4mm，而半高宽测量显示标准差<0.5mm。对于大于2×2cm的射野尺寸，OF测量显示标准差<1.5%。OF的中位数与近期文献一致。
所有考虑参数均显示出高度一致性。这项工作证实了多中心剂量学比对的重要性。W1 PSD可被视为小射野测量的良好候选者。
