Centre of Radiotherapy, National Institute of Oncology, Ráth György U. 7-9, Budapest, 1122, Hungary.
Doctoral College, Semmelweis University, Budapest, Hungary.
Radiat Oncol. 2024 Aug 14;19(1):109. doi: 10.1186/s13014-024-02504-8.
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.
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.
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.
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.
锥形束 CT（CBCT）常用于放射治疗中靶区定位。本研究旨在通过体外染色体剂量测定来确定 CBCT 剂量与后续治疗剂量的生物学效应。
从五名健康志愿者的外周血样本在两个体模（充满水的自制圆柱形体模和 Pure Image CTDI 体模）中用 6 MV 均整 FFF X 射线光子照射，剂量率为 800 MU/min，吸收剂量范围为 0.5 至 8 Gy。照射采用 6 MV 直线加速器（LINAC）进行，以生成剂量-反应校准曲线。在研究的第一部分，进行了 1-5 次 CBCT 成像；在第二部分，仅用 LINAC 给予 2 Gy 剂量；然后，在第三部分，模拟在线适应性放射治疗，进行 CBCT 和 2 Gy 照射的联合。用标准细胞遗传学技术从淋巴细胞培养物中制备中期，评估染色体畸变。用剂量-反应曲线从染色体畸变估算剂量。
在治疗前进行 CBCT 成像的样本暴露于 X 射线后，其染色体畸变和估算剂量均高于 2 Gy 治疗（实际）剂量，增加幅度取决于 CBCT 的数量：1-5 次 CBCT 对应 0.04-0.92 Gy，1 次 CBCT+2 Gy 对应 2.32 Gy，5 次 CBCT+2 Gy 对应 3.5 Gy。
对于 3 次 CBCT 和 2 Gy 治疗剂量的组合，基于染色体畸变的估算剂量比物理剂量高 24.8%，在计算可能增加第二次癌症风险的总治疗剂量时应考虑这一点。联合辐射效应的临床意义可能需要进一步研究。
