Department of Radiation Oncology, Stanford University, Stanford, California, USA.
RefleXion Medical, Hayward, California, USA.
J Appl Clin Med Phys. 2022 Jun;23(6):e13607. doi: 10.1002/acm2.13607. Epub 2022 Apr 28.
This study reports the beam commissioning results for the first clinical RefleXion Linac.
The X1 produces a 6 MV photon beam and the maximum clinical field size is 40 × 2 cm at source-to-axis distance of 85 cm. Treatment fields are collimated by a binary multileaf collimator (MLC) system with 64 leaves with width of 0.625 cm and y-jaw pairs to provide either a 1 or 2 cm opening. The mechanical alignment of the radiation source, the y-jaw, and MLC were checked with film and ion chambers. The beam parameters were characterized using a diode detector in a compact water tank. In-air lateral profiles and in-water percentage depth dose (PDD) were measured for beam modeling of the treatment planning system (TPS). The lateral profiles, PDDs, and output factors were acquired for field sizes from 1.25 × 1 to 40 × 2 cm field to verify the beam modeling. The rotational output variation and synchronicity were tested to check the gantry angle, couch motion, and gantry rotation.
The source misalignments were 0.049 mm in y-direction, 0.66% out-of-focus in x-direction. The divergence of the beam axis was 0.36 mm with a y-jaw twist of 0.03°. Clinical off-axis treatment fields shared a common center in y-direction were within 0.03 mm. The MLC misalignment and twist were 0.57 mm and 0.15°. For all measured fields ranging from the size from 1.25 × 1 to 40 × 2 cm , the mean difference between measured and TPS modeled PDD at 10 cm depth was -0.3%. The mean transverse profile difference in the field core was -0.3% ± 1.1%. The full-width half maximum (FWHM) modeling was within 0.5 mm. The measured output factors agreed with TPS within 0.8%.
This study summarizes our specific experience commissioning the first novel RefleXion linac, which may assist future users of this technology when implementing it into their own clinics.
本研究报告了第一台临床反射线性加速器的束流调试结果。
X1 产生 6MV 光子束，最大临床射野尺寸为源轴距 85cm 时的 40cm×2cm。治疗野由二进制多叶准直器（MLC）系统准直，该系统有 64 个宽度为 0.625cm 的叶片和 Y 形准直器对，可提供 1cm 或 2cm 的开口。辐射源、Y 形准直器和 MLC 的机械对准情况使用胶片和电离室进行了检查。使用紧凑型水箱中的二极管探测器对束参数进行了特征描述。在空气中进行了横向轮廓和水中百分深度剂量（PDD）的测量，以便对治疗计划系统（TPS）的束模型进行建模。为了验证束模型，对 1.25cm×1cm 至 40cm×2cm 大小的射野进行了横向轮廓、PDD 和输出因子的测量。为了检查旋转输出的变化和同步性，对旋转台角度、治疗床运动和旋转台旋转进行了测试。
源对准偏差为 y 方向 0.049mm，x 方向失焦 0.66%。束轴发散度为 0.36mm，Y 形准直器扭曲度为 0.03°。临床离轴治疗野在 y 方向共用一个中心，偏差在 0.03mm 以内。MLC 对准和扭曲偏差分别为 0.57mm 和 0.15mm。对于所有测量的射野，范围从 1.25cm×1cm 至 40cm×2cm，在 10cm 深度处，测量与 TPS 模型化 PDD 之间的平均差值为-0.3%。在射野中心，横向轮廓的平均差异为-0.3%±1.1%。全宽半高值（FWHM）建模偏差在 0.5mm 以内。测量的输出因子与 TPS 的差值在 0.8%以内。
本研究总结了我们在调试第一台新型反射线性加速器方面的具体经验，这可能有助于未来使用该技术的用户在将其引入自己的临床实践时提供参考。
