Department of Radiation Physics, The University of Texas M.D. Anderson Cancer Center, Houston, TX 77030, USA.
Med Phys. 2012 Mar;39(3):1239-46. doi: 10.1118/1.3681948.
Intensity-modulated proton therapy (IMPT) using spot scanned proton beams relies on the delivery of a large number of beamlets to shape the dose distribution in a highly conformal manner. The authors have developed a 3D system based on liquid scintillator to measure the spatial location, intensity, and depth of penetration (energy) of the proton beamlets in near real-time.
The detector system consists of a 20 × 20 × 20 cc liquid scintillator (LS) material in a light tight enclosure connected to a CCD camera. This camera has a field of view of 25.7 by 19.3 cm and a pixel size of 0.4 mm. While the LS is irradiated, the camera continuously acquires images of the light distribution produced inside the LS. Irradiations were made with proton pencil beams produced with a spot-scanning nozzle. Pencil beams with nominal ranges in water between 9.5 and 17.6 cm were scanned to irradiate an area of 10 × 10 cm square on the surface of the LS phantom. Image frames were acquired at 50 ms per frame.
The signal to noise ratio of a typical Bragg peak was about 170. Proton range measured from the light distribution produced in the LS was accurate to within 0.3 mm on average. The largest deviation seen between the nominal and measured range was 0.6 mm. Lateral position of the measured pencil beam was accurate to within 0.4 mm on average. The largest deviation seen between the nominal and measured lateral position was 0.8 mm; however, the accuracy of this measurement could be improved by correcting light scattering artifacts. Intensity of single proton spots were measured with precision ranging from 3 % for the smallest spot intensity (0.005 MU) to 0.5 % for the largest spot (0.04 MU).
Our LS detector system has been shown to be capable of fast, submillimeter spatial localization of proton spots delivered in a 3D volume. This system could be used for beam range, intensity and position verification in IMPT.
使用扫描点状质子束的强度调制质子治疗（IMPT）依赖于大量射束的传输，以高度适形的方式形成剂量分布。作者开发了一种基于液体闪烁体的 3D 系统，用于实时测量质子射束的空间位置、强度和穿透深度（能量）。
探测器系统由一个 20×20×20 cc 的密封液体闪烁体（LS）材料和一个与 CCD 相机相连的光密封外壳组成。该相机的视场为 25.7×19.3 厘米，像素大小为 0.4 毫米。当 LS 被照射时，相机连续获取 LS 内部产生的光分布图像。用扫描点状喷嘴产生的质子铅笔束进行照射。在水中名义射程为 9.5 至 17.6 厘米的铅笔束被扫描，以照射 LS 体模表面上 10×10 厘米的正方形区域。图像帧以 50 毫秒一帧的速度采集。
典型布拉格峰的信噪比约为 170。从 LS 中产生的光分布测量的质子射程平均精度在 0.3 毫米以内。看到的名义射程和测量射程之间的最大偏差为 0.6 毫米。测量铅笔束的横向位置平均精度在 0.4 毫米以内。看到的名义射程和测量横向位置之间的最大偏差为 0.8 毫米；然而，通过校正光散射伪影，该测量的精度可以提高。单质子点的强度用精度测量，最小点强度（0.005 MU）的精度范围为 3%，最大点（0.04 MU）的精度范围为 0.5%。
我们的 LS 探测器系统已被证明能够快速、亚毫米空间定位在 3D 体积中传输的质子点。该系统可用于 IMPT 的束流范围、强度和位置验证。
