Sharma Dayananda Shamurailatpam, Shaju P, Sawant Mayur B, Kaushik Suryakant
Department of Medical Physics, Apollo Proton Cancer Centre, Chennai, Tamil Nadu, India.
Department of Radiation Oncology, Kokilaben Dhirubhai Ambani Hospital and Medical Research Institute, Mumbai, Maharashtra, India.
J Med Phys. 2023 Apr-Jun;48(2):111-119. doi: 10.4103/jmp.jmp_93_22. Epub 2023 Jun 29.
To examine the dosimetric characteristics of circular cones, the accuracy of dose modeling and overall treatment delivery of two radiosurgery systems integrated on a linear accelerator (Linac).
The dosimetric characteristics of circular cones (4-17.5 mm) from Varian (VC) and BrainLAB (BLC) were measured for 6 MV flattening filter free beam from Edge linac using stereotactic field diode and 0.65 cc ionization chamber following established protocols. The Eclipse and iPlan modeled dose distribution for VCs and BLCs were validated with EBT3-film measurement. End-to-end tests were performed using stereotactic phantom having PTW 60008 diode connected to a Dose-1 electrometer.
The depth at dose maximum, TRP and dose at 10cm depth of the same size VC and BLC agree within ± 0.7 mm, ± 0.71% and ± 0.81% respectively. Full width at half maximum (FWHM) of any cone beyond 15 mm depth increases at 1% of nominal cone size per 10 mm depth. The penumbra of 4mm and 17.5mm VC at 15 mm depth was 1.1 mm and 1.50 mm. At 300 mm depth, penumbra increased by around 0.4 mm for 4 mm cone and up to 1 mm for cone size ≥12.5 mm. The VCs penumbra values were within ±1mm of the corresponding BLCs. Scatter factors for VCs varies from 0.609 to 0.841 and were within ± 1.0% of corresponding values of BLCs. Agreement between the Eclipse and iPlan computed dose fluence and the EBT3-film measured dose fluence was >98% (γ: 1%@1 mm), and the absolute dose difference was ≤ 2.2%, except for the 4 mm cone in which it was >96% and ≤4.83%. Target localization using cone-beam computed tomography was accurate within ± 0.8 mm and ± 0.3° in translation and rotation. The end-to-end dose delivery accuracy for both radiosurgery systems was within ± 3.62%.
The dosimetric characteristics of Varian and BLC cones of same diameter was comparable. Both Eclipse and iPlan cone planning system modeled dose fluences agree well with the EBT3 film measurement. The end-to-end tests revealed an excellent target localization accuracy of Edge linac with satisfactory and comparable absolute dose agreement between Varian and BLC radiosurgery systems and hence these can be interchanged on edge linac.
研究集成在线性加速器（直线加速器）上的两种放射外科系统的圆形准直器的剂量学特性、剂量建模准确性及整体治疗交付情况。
按照既定方案，使用立体定向场二极管和0.65 cc电离室，对瓦里安（VC）和BrainLAB（BLC）的圆形准直器（4 - 17.5 mm）在Edge直线加速器的6 MV无均整器射束下的剂量学特性进行测量。用EBT3胶片测量对Eclipse和iPlan为VC和BLC建模的剂量分布进行验证。使用连接到剂量仪 - 1静电计的PTW 60008二极管的立体定向体模进行端到端测试。
相同尺寸的VC和BLC在剂量最大值处的深度、组织空气比（TRP）以及10 cm深度处的剂量分别在±0.7 mm、±0.71%和±0.81%范围内一致。深度超过15 mm的任何准直器的半高宽（FWHM）每10 mm深度以标称准直器尺寸的1%增加。15 mm深度处4 mm和17.5 mm VC的半值层分别为1.1 mm和1.50 mm。在300 mm深度处，4 mm准直器的半值层增加约0.4 mm，准直器尺寸≥12.5 mm的增加高达1 mm。VC的半值层值在相应BLC的±1 mm范围内。VC的散射因子在0.609至0.841之间，且在BLC相应值的±1.0%范围内。Eclipse和iPlan计算的剂量注量与EBT3胶片测量的剂量注量之间的一致性>98%（γ：1%@1 mm），绝对剂量差异≤2.2%，4 mm准直器除外，其一致性>96%且≤4.83%。使用锥形束计算机断层扫描进行的靶区定位在平移和旋转方面的精度分别在±0.8 mm和±0.3°以内。两种放射外科系统的端到端剂量交付精度在±3.62%以内。
相同直径的瓦里安和BLC准直器的剂量学特性具有可比性。Eclipse和iPlan准直器规划系统建模的剂量注量与EBT3胶片测量结果吻合良好。端到端测试显示Edge直线加速器具有出色的靶区定位精度，瓦里安和BLC放射外科系统之间的绝对剂量一致性令人满意且具有可比性，因此它们可以在Edge直线加速器上互换。
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