Lechner Wolfgang, Wesolowska Paulina, Azangwe Godfrey, Arib Mehenna, Alves Victor Gabriel Leandro, Suming Luo, Ekendahl Daniela, Bulski Wojciech, Samper José Luis Alonso, Vinatha Sumanth Panyam, Siri Srimanoroth, Tomsej Milan, Tenhunen Mikko, Povall Julie, Kry Stephen F, Followill David S, Thwaites David I, Georg Dietmar, Izewska Joanna
International Atomic Energy Agency, Vienna, Austria.
Medical University of Vienna, Department of Radiation Oncology, Vienna, Austria.
Phys Imaging Radiat Oncol. 2018 Mar 6;5:58-63. doi: 10.1016/j.phro.2018.02.005. eCollection 2018 Jan.
An audit methodology for verifying the implementation of output factors (OFs) of small fields in treatment planning systems (TPSs) used in radiotherapy was developed and tested through a multinational research group and performed on a national level in five different countries.
Centres participating in this study were asked to provide OFs calculated by their TPSs for 10 × 10 cm, 6 × 6 cm, 4 × 4 cm, 3 × 3 cm and 2 × 2 cm field sizes using an SSD of 100 cm. The ratio of these calculated OFs to reference OFs was analysed. The action limit was ±3% for the 2 × 2 cm field and ±2% for all other fields.
OFs for more than 200 different beams were collected in total. On average, the OFs for small fields calculated by TPSs were generally larger than measured reference data. These deviations increased with decreasing field size. On a national level, 30% and 31% of the calculated OFs of the 2 × 2 cm field exceeded the action limit of 3% for nominal beam energies of 6 MV and for nominal beam energies higher than 6 MV, respectively.
Modern TPS beam models generally overestimate the OFs for small fields. The verification of calculated small field OFs is a vital step and should be included when commissioning a TPS. The methodology outlined in this study can be used to identify potential discrepancies in clinical beam models.
通过一个跨国研究小组开发并测试了一种用于验证放射治疗中使用的治疗计划系统（TPS）中小野输出因子（OFs）实施情况的审核方法，并在五个不同国家的国家层面上进行了实施。
要求参与本研究的中心使用100 cm的源皮距（SSD），提供其TPS针对10×10 cm、6×6 cm、4×4 cm、3×3 cm和2×2 cm射野尺寸计算的OFs。分析这些计算得到的OFs与参考OFs的比值。对于2×2 cm射野，行动限值为±3%，对于所有其他射野，行动限值为±2%。
总共收集了200多个不同射束的OFs。平均而言，TPS计算的小野OFs通常大于测量的参考数据。这些偏差随着射野尺寸的减小而增加。在国家层面上，对于标称束能量为6 MV和高于6 MV的情况，2×2 cm射野计算得到的OFs分别有30%和31%超过了3%的行动限值。
现代TPS射束模型通常高估了小野的OFs。验证计算得到的小野OFs是至关重要的一步，在调试TPS时应予以纳入。本研究中概述的方法可用于识别临床射束模型中的潜在差异。
