目的:锥形束计算机断层扫描(CBCT)通常用于放射治疗以定位靶区。我们研究的目的是通过使用体外染色体剂量学来确定CBCT剂量与后续治疗剂量相比的生物学效应。
方法:将来自五名健康志愿者的外周血样本在两个体模中照射(内部填充的水制成的圆柱形,和纯图像CTDI幻影),具有6MVFFFX射线光子,剂量率为800MU/min,吸收剂量范围为0.5至8Gy。用6MV线性加速器(LINAC)进行照射以产生剂量-响应校准曲线。在调查的第一部分,使用1-5个CBCT成像,在第二个,只有2Gy剂量的LINAC,然后,在第三部分,采用CBCT和2Gy联合照射,模拟在线适应放射治疗.中期从淋巴细胞培养物中制备,使用标准的细胞遗传学技术,和染色体畸变进行了评估。使用剂量反应曲线从染色体畸变计算估计剂量。
结果:治疗前接受CBCT成像的X射线样本显示出高于2Gy治疗(实际)剂量的染色体像差和估计剂量,增加的幅度取决于CBCT的数量:1-5个CBCT对应于0.04-0.92Gy,1CBCT+2Gy至2.32Gy,和5个CBCT+2Gy至3.5Gy。
结论:基于染色体畸变的估计剂量比物理剂量高24.8%,对于3个CBCT和治疗2Gy剂量的组合,在计算可能增加第二次癌症风险的总治疗剂量时,应考虑到这一点。联合辐射效应的临床意义可能需要进一步研究。
OBJECTIVE: Cone beam computed tomography (CBCT) is routinely used in radiotherapy to localize target volume. The aim of our study was to determine the biological effects of CBCT dose compared to subsequent therapeutic dose by using in vitro chromosome dosimetry.
METHODS: Peripheral blood samples from five healthy volunteers were irradiated in two phantoms (water filled in-house made cylindrical, and Pure Image CTDI phantoms) with 6 MV FFF X-ray photons, the dose rate was 800 MU/min and the absorbed doses ranged from 0.5 to 8 Gy. Irradiation was performed with a 6 MV linear accelerator (LINAC) to generate a dose-response calibration curve. In the first part of the investigation, 1-5 CBCT imaging was used, in the second, only 2 Gy doses were delivered with a LINAC, and then, in the third part, a combination of CBCT and 2 Gy irradiation was performed mimicking online adapted radiotherapy treatment. Metaphases were prepared from lymphocyte cultures, using standard cytogenetic techniques, and chromosomal aberrations were evaluated. Estimate doses were calculated from chromosome aberrations using dose-response curves.
RESULTS: Samples exposed to X-ray from CBCT imaging prior to treatment exhibited higher chromosomal aberrations and Estimate dose than the 2 Gy therapeutic (real) dose, and the magnitude of the increase depended on the number of CBCTs: 1-5 CBCT corresponded to 0.04-0.92 Gy, 1 CBCT + 2 Gy to 2.32 Gy, and 5 CBCTs + 2 Gy to 3.5 Gy.
CONCLUSIONS: The estimated dose based on chromosomal aberrations is 24.8% higher than the physical dose, for the combination of 3 CBCTs and the therapeutic 2 Gy dose, which should be taken into account when calculating the total therapeutic dose that could increase the risk of a second cancer. The clinical implications of the combined radiation effect may require further investigation.