Weidlich Georg A, Chung Woody, Kolli Srejitha, Thirunarayanan Ishwarya, Loysel Thibaut
Radiation Oncology, National Medical Physics and Dosimetry Company, Palo Alto, USA.
LINAC Development, Dosimetry, and Validation, Zap Surgical Systems, Inc., San Carlos, USA.
Cureus. 2021 Mar 18;13(3):e13972. doi: 10.7759/cureus.13972.
Various small-field radiation dose detectors were systematically compared and their impact on measured beam performance of the ZAP-X® dedicated stereotactic radiosurgery system (ZAP Surgical Systems, Inc., San Carlos, CA, USA) was determined. Three Physikalische Technische Werkstaetten (PTW) diodes, i.e., the microSilicon, the microDiamond, and the Stereotactic Radiosurgery (SRS) diode detectors of (PTW-Freiburg, Freiburg, Germany), as well as Gafchromic™ External Beam Therapy 3 (EBT) film (Ashland, Inc., Wilmington, DE, USA), were used and compared to arrive at a recommended standard for this critical component of small-field beam measurements. Beam profiles, including the dose fall-off region near the edge of the beam, were measured with the PTW diodes and EBT3 film and subsequently contrasted. The impact of detector physical and dosimetric characteristics on the results of the measurements was investigated and compared with film measurements. The beam penumbra was used to quantify the dose fall-off. The measurement acquired with the diodes and film showed the most significant differences in the fall-off region near the field edge. The film-based measurements clearly showed the steepest dose gradient verified by the penumbra value of 1.21 mm, followed by the SRS diode with 1.60 mm, the microSilicon diode with 1.67 mm, and the microDiamond diode with 1.83 mm. A clear correlation of each detector's sensitive area with the penumbra was found, with the microDiamond detector at 2.2 mm diameter sensitive area having the largest penumbra, followed by the microSilicon and SRS diodes. Beam measurements for the purposes of system characterization or treatment planning system beam data acquisition depend, to a large extent, on detector characteristics. This is especially true for small-field dosimetry performed during stereotactic radiosurgery beam measurements. Careful consideration should be practiced which allows for the measurements to represent true beam characteristics and minimize the impact of the detector on the measurements. We conclude that film should be considered the reference method for such measurements with the ZAP-X due to its smallest physical measurement resolution of 23.1 µm. Potential drawbacks to this methodology are the need to calibrate the film relative to the dose and possible problems with saturation and non-linear film response for very high and very low optical densities.
对各种小射野辐射剂量探测器进行了系统比较，并确定了它们对ZAP-X®专用立体定向放射外科系统（美国加利福尼亚州圣卡洛斯市ZAP Surgical Systems公司）测量射束性能的影响。使用了三个德国弗赖堡市Physikalische Technische Werkstaetten（PTW）公司的二极管，即微硅二极管、微金刚石二极管和立体定向放射外科（SRS）二极管探测器，以及美国特拉华州威尔明顿市Ashland公司的Gafchromic™ 外照射治疗3（EBT）胶片，并进行比较，以得出这一小射野射束测量关键部件的推荐标准。使用PTW二极管和EBT3胶片测量了射束剖面，包括射束边缘附近的剂量下降区域，随后进行了对比。研究了探测器物理和剂量学特性对测量结果的影响，并与胶片测量结果进行了比较。用射束半值层来量化剂量下降。用二极管和胶片进行的测量显示在场边缘附近的下降区域差异最为显著。基于胶片的测量清楚地显示出最陡的剂量梯度，其半值层值为1.21 mm，其次是SRS二极管，半值层为1.60 mm，微硅二极管为1.67 mm，微金刚石二极管为1.83 mm。发现每个探测器的灵敏面积与半值层有明显的相关性，直径为2.2 mm灵敏面积的微金刚石探测器半值层最大，其次是微硅二极管和SRS二极管。用于系统特性描述或治疗计划系统射束数据采集的射束测量在很大程度上取决于探测器特性。在立体定向放射外科射束测量期间进行的小射野剂量测定尤其如此。应谨慎考虑，使测量能够代表真实的射束特性，并尽量减少探测器对测量的影响。我们得出结论，由于其最小物理测量分辨率为23.1 µm，胶片应被视为使用ZAP-X进行此类测量的参考方法。这种方法的潜在缺点是需要相对于剂量校准胶片，以及对于非常高和非常低的光密度可能存在的饱和和胶片非线性响应问题。
