Mutaf Y, Yu C, Zhang J, Yi B, Prado K, D'Souza W, Regine W, Feigenberg S
University of Maryland School of Medicine, Baltimore, MD.
Xcision Medical Systems, Columbia, MD.
Med Phys. 2012 Jun;39(6Part16):3796. doi: 10.1118/1.4735488.
A dedicated stereotactic irradiation device, the GammaPodTM, was developed to treat early stage breast cancer. This study presents the first description of the dosimetric and geometric characteristics from the prototype unit.
The GammaPod stereotactic radiotherapy device is an assembly of a hemi-spherical source carrier containing 36 Co-60 sources, a tungsten collimator, a dynamically controlled treatment table and a breast immobilization cup embedded with a stereotactic coordinate system. The source carrier and the variable-size collimator rotate synchronously to form 36 non-coplanar, concentric arcs focused at the isocenter. The treatment table enables motion in three dimensions facilitating continuous dose painting in comparison to a sphere packing approach. Geometric and dosimetric evaluations and a method for absorbed dose calibration are provided. Dosimetric verifications of the dynamically delivered plans are performed for eight patients in hypothetical pre-op, post-op and dose painting treatment scenarios.
Loaded with a cumulative activity of 4320 Ci, the GammaPod unit delivers 5.31 Gy/min at the isocenter. Due to non-coplanar beam arrangement and dynamic dose shaping features, the GammaPod delivers uniform doses to the targets with excellent conformity. The spatial accuracy of the device is less than 1 mm. Single shot profiles with the 25 mm collimator are measured with radiochromic film and found to be in good agreement with respect to the MC based calculations (congruence of FWHM less than 1 mm). Dosimetric verifications corresponding to all treatment plans corresponding to three target scenarios for each of the eight patients demonstrated Gamma index pass rates greater than 97%.
The first description of the dosimetric and geometric evaluation of the GammaPod was performed. The observed level of agreement between the treatment planning system calculations and dosimetric measurements has confirmed that the system can deliver highly complex treatment plans with remarkable geometric and dosimetric accuracy. C Yu and J Zhang have commercial affiliations with Xcision Medical Systems.
研发了一种专用立体定向放射治疗设备——伽马刀（GammaPodTM），用于治疗早期乳腺癌。本研究首次描述了该原型设备的剂量学和几何特征。
伽马刀立体定向放射治疗设备由一个包含36个钴 - 60源的半球形源载体、一个钨准直器、一个动态控制的治疗床以及一个嵌入立体定向坐标系的乳房固定杯组成。源载体和可变尺寸准直器同步旋转，形成36条非共面、同心的弧形束，聚焦于等中心。与球形填充方法相比，治疗床能够在三个维度上移动，便于进行连续剂量描绘。提供了几何和剂量学评估以及吸收剂量校准方法。针对八名患者，在假设的术前、术后和剂量描绘治疗场景下，对动态交付计划进行剂量学验证。
伽马刀设备装载的总活度为4320居里，在等中心处的剂量率为5.31戈瑞/分钟。由于非共面束排列和动态剂量塑形特性，伽马刀能够为靶区提供均匀剂量，适形性良好。该设备的空间精度小于1毫米。使用放射变色胶片测量了25毫米准直器的单次照射剂量分布曲线，发现与基于蒙特卡罗模拟的计算结果吻合良好（半高宽一致性小于1毫米）。对八名患者中每种三个靶区场景对应的所有治疗计划进行的剂量学验证表明，伽马指数通过率大于97%。
对伽马刀进行了首次剂量学和几何评估描述。治疗计划系统计算结果与剂量学测量结果之间观察到的一致性水平证实，该系统能够以卓越的几何和剂量学精度交付高度复杂的治疗计划。C Yu和J Zhang与Xcision Medical Systems有商业关联。
