University of Oklahoma Health Sciences Center.
J Appl Clin Med Phys. 2014 May 8;15(3):4638. doi: 10.1120/jacmp.v15i3.4638.
The purpose of this study is to investigate an effect of angular dependence and calibration field size of MapCHECK 2 on RapidArc QA for 6, 8, 10, and 15 MV. The angular dependence was investigated by comparing MapCHECK 2 measurements in MapPHAN-MC2 to the corresponding Eclipse calculations every 10° using 10× 10 cm2 and 3 × 3 cm2 fields. Fourteen patients were selected to make RapidArc plans using the four energies, and verification plans were delivered to two phantom setups: MapCHECK 2/MapPHAN phantom (MapPHAN QA) and MapCHECK 2 on an isocentric mounting fixture (IMF QA). Migration of MapCHECK 2 on IMF was simulated by splitting arcs every 10° and displacing an isocenter of each partial arc in the Eclipse system (IMFACTUAL QA). To investigate the effect of calibration field size, MapCHECK 2 was calibrated by two field sizes (10 × 10 cm2 and 3 × 3 cm2) and applied to all QA measurements. The γ test was implemented using criteria of 1%/1 mm, 2%/2 mm, and 3%/3 mm. A mean dose of all compared points for each plan was compared with respect to a mean effective field size of the RapidArc plan. The angular dependence was considerably high at gantry angles of 90° ± 10° and 270° ± 10° (for 10 × 10/3 × 3 cm2 at 90°, 30.6% ± 6.6%/33.4%± 5.8% (6 MV), 17.3% ± 5.3%/15.0% ± 6.8% (8 MV), 8.9%± 2.9%/7.8% ± 3.2% (10 MV), and 2.2% ± 2.3%/-1.3% ± 2.6% (15 MV)). For 6 MV, the angular dependence significantly deteriorated the γ passing rate for plans of large field size in MapPHAN QA (< 90% using 3%/3 mm); however, these plans passed the γ test in IMFACTUAL QA (> 95%). The different calibration field sizes did not make any significant dose difference for both MapPHAN QA and IMFACTUAL QA. For 8, 10, and 15 MV, the angular dependence does not make any clinically meaningful impact on MapPHAN QA. Both MapPHAN QA and IMFACTUAL QA presented clinically acceptable γ passing rates using 3%/3 mm. MapPHAN QA showed better passing rates than IMFACTUAL QA for the tighter criteria. The 10 × 10 cm2 calibration showed better agreement for plans of small effective field size (< 5 × 5 cm2) in MapPHAN QA. There was no statistical difference between IMF QA and IMFACTUAL QA. In conclusion, MapPHAN QA is not recommended for plans of large field size, especially for 6 MV, and MapCHECK2 should be calibrated using a field size similar to a mean effective field size of a RapidArc plan for better agreement for IMF QA.
本研究旨在探讨 MapCHECK 2 的角度依赖性和校准场大小对 6、8、10 和 15 MV 的 RapidArc QA 的影响。通过将 MapCHECK 2 在 MapPHAN-MC2 中的测量值与 Eclipse 计算值进行比较，每 10°使用 10×10 cm2 和 3×3 cm2 场来研究角度依赖性。选择了 14 名患者使用四种能量进行 RapidArc 计划，验证计划被传送到两个体模设置：MapCHECK 2/MapPHAN 体模（MapPHAN QA）和等中心安装夹具上的 MapCHECK 2（IMF QA）。通过将每个部分弧的等中心在 Eclipse 系统中移动 10°并分裂弧来模拟 MapCHECK 2 在 IMF 上的移动（IMFACTUAL QA）。为了研究校准场大小的影响，使用两种场大小（10×10 cm2 和 3×3 cm2）对 MapCHECK 2 进行校准，并将其应用于所有 QA 测量。使用 1%/1mm、2%/2mm 和 3%/3mm 的标准执行γ测试。对于每个计划的所有比较点的平均剂量相对于 RapidArc 计划的平均有效场大小进行比较。在 90°±10°和 270°±10°的龙门角度下，角度依赖性相当高（对于 10×10/3×3 cm2，在 90°时，30.6%±6.6%/33.4%±5.8%（6 MV），17.3%±5.3%/15.0%±6.8%（8 MV），8.9%±2.9%/7.8%±3.2%（10 MV）和 2.2%±2.3%/-1.3%±2.6%（15 MV））。对于 6 MV，角度依赖性显著降低了 MapPHAN QA 中大面积计划的γ通过率（使用 3%/3mm 时低于 90%）;然而，这些计划在 IMFACTUAL QA 中通过了γ测试（大于 95%）。不同的校准场大小对 MapPHAN QA 和 IMFACTUAL QA 都没有产生任何显著的剂量差异。对于 8、10 和 15 MV，角度依赖性对 MapPHAN QA 没有任何有临床意义的影响。使用 3%/3mm，MapPHAN QA 和 IMFACTUAL QA 都呈现出可接受的γ通过率。对于更严格的标准，MapPHAN QA 的通过率优于 IMFACTUAL QA。对于小有效场大小（<5×5 cm2）的计划，10×10 cm2 校准在 MapPHAN QA 中显示出更好的一致性。IMF QA 和 IMFACTUAL QA 之间没有统计学差异。总之，MapPHAN QA 不推荐用于大面积计划，特别是对于 6 MV，并且对于更好的 IMF QA 一致性，MapCHECK 2 应使用类似于 RapidArc 计划的平均有效场大小的场大小进行校准。
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