Ponmalar Retna, Manickam Ravikumar, Ganesh K M, Saminathan Sathiyan, Raman Arun, Godson Henry Finlay
Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Bengaluru, Karnataka; Department of Radiotherapy, Christian Medical College, Vellore, Tamil Nadu, India.
Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Bengaluru, Karnataka, India.
J Cancer Res Ther. 2017 Apr-Jun;13(2):304-312. doi: 10.4103/0973-1482.199432.
The modern radiotherapy techniques impose new challenges for dosimetry systems with high precision and accuracy in in vivo and in phantom dosimetric measurements. The knowledge of the basic characterization of a dosimetric system before patient dose verification is crucial. This incites the investigation of the potential use of nanoDot optically stimulated luminescence dosimeter (OSLD) for application in radiotherapy with therapeutic photon beams.
Measurements were carried out with nanoDot OSLDs to evaluate the dosimetric characteristics such as dose linearity, dependency on field size, dose rate, energy and source-to-surface distance (SSD), reproducibility, fading effect, reader stability, and signal depletion per read out with cobalt-60 (60 Co) beam, 6 and 18 MV therapeutic photon beams. The data acquired with OSLDs were validated with ionization chamber data where applicable.
Good dose linearity was observed for doses up to 300 cGy and above which supralinear behavior. The standard uncertainty with field size observed was 1.10% ± 0.4%, 1.09% ± 0.34%, and 1.2% ± 0.26% for 6 MV, 18 MV, and 60 Co beam, respectively. The maximum difference with dose rate was 1.3% ± 0.4% for 6 MV and 1.4% ± 0.4% for 18 MV photon beams. The largest variation in SSD was 1.5% ± 1.2% for 60 Co, 1.5% ± 0.9% for 6 MV, and 1.5% ± 1.3% for 18 MV photon beams. The energy dependence of OSL response at 18 MV and 60 Co with 6 MV beam was 1.5% ± 0.7% and 1.7% ± 0.6%, respectively. In addition, good reproducibility, stability after the decay of transient signal, and predictable fading were observed.
The results obtained in this study indicate the efficacy and suitability of nanoDot OSLD for dosimetric measurements in clinical radiotherapy.
现代放射治疗技术对剂量测定系统提出了新的挑战，要求其在体内和模体剂量测量中具有高精度和准确性。在对患者进行剂量验证之前，了解剂量测定系统的基本特性至关重要。这激发了对纳米Dot光激励发光剂量计（OSLD）在治疗性光子束放射治疗中潜在应用的研究。
使用纳米Dot OSLD进行测量，以评估剂量学特性，如剂量线性、对射野大小、剂量率、能量和源皮距（SSD）的依赖性、重复性、衰退效应、读数器稳定性以及每次读出时的信号损耗，使用钴-60（60Co）射线束、6和18MV治疗性光子束。在适用的情况下，用OSLD获得的数据与电离室数据进行了验证。
对于高达300cGy的剂量观察到良好的剂量线性，高于此剂量则出现超线性行为。对于6MV、18MV和60Co射线束，观察到的射野大小标准不确定度分别为1.10%±0.4%、1.09%±0.34%和1.2%±0.26%。对于6MV光子束，与剂量率的最大差异为1.3%±0.4%，对于18MV光子束为1.4%±0.4%。对于60Co，SSD的最大变化为1.5%±1.2%，对于6MV为1.5%±0.9%，对于18MV光子束为1.5%±1.3%。18MV和60Co时OSL响应相对于6MV射线束的能量依赖性分别为1.5%±0.7%和1.7%±0.6%。此外，还观察到良好的重复性、瞬态信号衰减后的稳定性以及可预测的衰退。
本研究获得的结果表明纳米Dot OSLD在临床放射治疗剂量测量中的有效性和适用性。
