Ding G, Munro P
Vanderbilt University, Nashville, TN.
Varian Medical Systems, iLab GmbH, Switzerland.
Med Phys. 2012 Jun;39(6Part6):3661. doi: 10.1118/1.4734874.
To compare the IGRT doses from MV, kV and CBCT images.
kV imaging systems integrated into Varian Trilogy and TrueBeam accelerators were modeled using BEAMnrc/DOSXYZnrc Monte Carlo codes and the dose to calibration phantoms for a variety of kV beams(kVp, bow-tie filters, etc.) were calculated. The doses to the same phantoms and kV beams were then measured experimentally using calibrated ion-chambers.The "calibrated" Monte Carlo kV beams were used to calculate dose to CT images of patients. Organ doses were analyzed using DVHs.
The doses to the prostate are 0.015 and 2.2cGy using AP kV and MV images; are 0.06 and 2.3cGy using lateral kV and MV images; and, are 1.7 cGy using CBCT images. For head and neck images, the doses to the eye are 0.08 and 0.001 cGy using AP and PA kV images; are 2.3 and 1.8cGy using AP and PA MV images; are 0.001 and 2.4cGy for lateral kV and MV images; and, are 0.2 cGy for CBCT images. For kV radiographs, organ doses can be further reduced, by over 30%, by using bow-tie filters. CBCT doses to the prostate are 1.6 and 0.9cGy for OBI and TrueBeam pelvis scans; a >40% dose reduction for the same image quality. For OBI CBCT head scans the doses to the eye and brain stem are 0.2 and 2.8cGy, respectively.
Due to the low penetration of kV beams,selecting beam angles so that the sensitive organs are near the beam exit, and/or using bow-tie filters, can substantially reduce organ doses when using kV radiographs. For daily positioning of pediatric brain patient with a set of orthogonal kV images, a CBCT scan, or a set of orthogonal MV images, the doses to the eyes are 0.1, 0.2, and 4.7 cGy, respectively.
比较来自兆伏（MV）、千伏（kV）和锥形束CT（CBCT）图像的图像引导放射治疗（IGRT）剂量。
使用BEAMnrc/DOSXYZnrc蒙特卡罗代码对集成在瓦里安Trilogy和TrueBeam加速器中的千伏成像系统进行建模，并计算各种千伏束（千伏峰值、蝴蝶结滤波器等）对校准体模的剂量。然后使用校准的电离室通过实验测量相同体模和千伏束的剂量。使用“校准”的蒙特卡罗千伏束来计算患者CT图像的剂量。使用剂量体积直方图（DVHs）分析器官剂量。
使用前后位千伏和兆伏图像时，前列腺的剂量分别为0.015和2.2厘戈瑞（cGy）；使用侧位千伏和兆伏图像时，分别为0.（此处原文有误，推测为0.06和2.3）cGy；使用CBCT图像时为1.7 cGy。对于头颈部图像，使用前后位和后前位千伏图像时，眼睛的剂量分别为0.08和0.001 cGy；使用前后位和后前位兆伏图像时，分别为2.3和1.8 cGy；使用侧位千伏和兆伏图像时，分别为0.001和2.4 cGy；使用CBCT图像时为0.2 cGy。对于千伏射线照片，通过使用蝴蝶结滤波器，器官剂量可进一步降低超过30%。对于CBCT，在OBI和TrueBeam骨盆扫描中，前列腺的剂量分别为1.6和0.9 cGy；在相同图像质量下剂量降低超过40%。对于OBI CBCT头部扫描，眼睛和脑干的剂量分别为0.2和2.8 cGy。
由于千伏束的低穿透性，选择使敏感器官靠近束流出口的束角，和/或使用蝴蝶结滤波器，在使用千伏射线照片时可大幅降低器官剂量。对于小儿脑部患者每日使用一组正交千伏图像、一次CBCT扫描或一组正交兆伏图像进行定位时，眼睛的剂量分别为0.1、0.2和4.7 cGy。
