用于放疗剂量验证的新型片状Presage胶体剂量计特性研究

Dose response characterization of novel presage sheets for radiotherapy dose verification

目的明确用于放疗剂量验证的新型片状Presage胶体剂量计的吸收光谱、剂量线性、量程、稳定性等关键剂量响应特性。方法使用放疗加速器对同批次片状Presage剂量计进行系列照射实验,使用分光光度计测量照射前后剂量计在400-700 nm可见光范围内的吸收光谱,使用胶片平板扫描仪测量照射前后R-G-B 3通道的吸光度变化。结果片状Presage在628 nm处有明显吸收峰且峰值吸光度随受照剂量呈显著线性变化趋势(R^2=0.9999),而在490 nm附近存在平缓吸收谷且谷区吸光度随受照剂量变化不大。胶体平板扫描仪R通道的吸光度测量灵敏度远大于G与B通道,在<10 Gy范围内,R通道吸光度随受照剂量呈高度线性变化(R^2=0.9999),而在大量程范围则呈显著二次变化趋势(R^2=0.9999)。该剂量计的量程范围>94.6 Gy,在照射后1 h内吸光度变化可忽略,之后则呈现缓慢上升趋势,上升速度与受照剂量呈正相关,同时,未发现剂量梯度区出现梯度模糊现象。结论新型片状Presage胶体剂量计在一定范围内具有良好剂量线性,量程大、梯度保持性好、无分割效应,提示在大分割多靶点放疗的积分剂量验证中具有潜在应用优势。

Objective To characterize the key dose response properties of the novel presage sheet dosimeters for radiotherapy dose verification,including absorption spectra,linearity,dose range and stability.Methods The same batch of presage sheet dosimeters were irradiated by a radiotherapy linac.The absorption spectra within 400-700 nm were read out with a spectrophotometer,and the R-G-B3 absorption changes read out with a film flatbed scanner was compared before and after irradiation.Results An absorption peak was clearly identified at 628 nm,where absorptions change in high linearity with delivered doses(R^2=0.9999).A flat valley region is identified around 490 nm,where dose induced absorption changes were negligible.The readout sensitivity of the R-channel of the flatbed scanner was higher than both in green and blue channels.In the dose range below 10 Gy,the R-channel absorptions are in significant linearity with doses(R^2=0.9999),with absorptions change in an obvious quadratic trend in the range beyond 10 Gy(R^2=0.9999).The dose range of presage sheets was more than 94.6 Gy.The absorptions were well preserved within 1 h post-irradation,and then are shown to increase gradually,where the increase speeds are dose-related.The post-irradiation integrity of dose falloff gradients are shown with negligible gradient blurring.Conclusions The novel presage sheets shown to have reasonable dose response linearity,large dose range,desirable post-irradiation dose gradient integrity and negligible fractionation effect,which indicates its great potentials in integral dose verification of high-dose and multiple target radiotherapy deliveries.