Kannan Mageshraja, Saminathan Sathiyan, Chandraraj Varatharaj, Raj D Gowtham, Ganesh K M
Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Bengaluru, Karnataka, India.
J Med Phys. 2023 Jul-Sep;48(3):281-288. doi: 10.4103/jmp.jmp_59_23. Epub 2023 Sep 18.
In this study, a 6MV flattening filter (FF) and 6MV FF Free (FFF) photon beam small-field output factors (OF) were measured with various collimators using different detectors. The corrected OFs were compared with the treatment planning system (TPS) calculated OFs.
OF measurements were performed with four different types of collimators: Varian Millennium multi-leaf collimator (MLC), Elekta Agility MLC, Apex micro-MLC (mMLC) and a stereotactic cone. Ten detectors (four ionization chambers and six diodes) were used to perform the OF measurements at a depth of 10 cm with a source-to-surface distance of 90 cm. The corrected OF was calculated from the measurements. The corrected OFs were compared with existing TPS-generated OFs.
The use of detector-specific output correction factor (OCF) in the PTW diode P detector reduced the OF uncertainty by <4.1% for 1 cm × 1 cm S. The corrected OF was compared with TPS calculated OF; the maximum variation with the IBA CC01 chamber was 3.75%, 3.72%, 1.16%, and 0.90% for 5 mm stereotactic cone, 0.49 cm × 0.49 cm Apex mMLC, 1 cm × 1 cm Agility MLC, and 1 cm × 1 cm Millennium MLC, respectively.
The technical report series-483 protocol recommends that detector-specific OCF should be used to calculate the corrected OF from the measured OF. The implementation of OCF in the TPS commissioning will reduce the small-field OF variation by <3% for any type of detector.
在本研究中，使用不同探测器，通过各种准直器测量6兆伏扁平滤过器（FF）和6兆伏无FF（FFF）光子束小射野输出因子（OF）。将校正后的OF与治疗计划系统（TPS）计算的OF进行比较。
使用四种不同类型的准直器进行OF测量：瓦里安千年多叶准直器（MLC）、医科达敏捷MLC、顶点微型MLC（mMLC）和立体定向锥。使用十个探测器（四个电离室和六个二极管）在源皮距为90厘米、深度为10厘米处进行OF测量。根据测量结果计算校正后的OF。将校正后的OF与现有的TPS生成的OF进行比较。
在PTW二极管P探测器中使用特定探测器输出校正因子（OCF），对于1厘米×1厘米的射野，OF不确定性降低了<4.1%。将校正后的OF与TPS计算的OF进行比较；对于5毫米立体定向锥、0.49厘米×0.49厘米顶点mMLC、1厘米×1厘米敏捷MLC和1厘米×1厘米千年MLC，与IBA CC01电离室相比，最大变化分别为3.75%、3.72%、1.16%和0.90%。
技术报告系列-483协议建议应使用特定探测器的OCF从测量的OF计算校正后的OF。在TPS调试中实施OCF将使任何类型探测器的小射野OF变化降低<3%。
