EBT3和EDR2胶片对扫描束碳离子剂量的响应研究

EBT3 and EDR2 film dosimetry for scanning carbon ion beams

目的 研究EBT3和EDR2胶片对于不同传能线密度和剂量碳离子响应。方法 EBT3和EDR2胶片采用两种方法进行光密度-剂量校准：一是将胶片放置在固体水与束流垂直测量深度，每张胶片接受同能量不同剂量碳离子照射；二是将多张完整胶片放置与束流垂直固体水不同深度，采用碳离子单次照射，在胶片不同区域形成不同物理剂量校准野。结果 在测量范围内，EBT3胶片光密度-剂量校准曲线（下称校准曲线）呈双曲线型，不同传能线密度校准曲线间最大差异为±17%；而EDR2校准曲线呈直线形，不同传能线密度间差异为±27.4%；两种胶片剂量响应均受碳离子在胶片测量深度传能线密度影响，传能线密度越大，胶片光密度响应越低；EBT3胶片灵敏度与剂量呈反比，但EDR2胶片灵敏度则与剂量无关。结论 EBT3胶片响应受传能线密度和剂量双重影响，限制了其在碳离子剂量测量方面的应用。EDR2胶片响应虽受传能线密度影响更大，但受单能碳离子照射时，由于其灵敏度与剂量无关，可用于单能碳离子剂量测量。

Objective To investigate EBT3 and EDR2 film responses to different linear energy transfers （LETs） and doses from carbon ion beams. Methods EBT3 and EDR2 films were calibrated by two methods. In the first method, films were placed at the same depth within a phantom and irradiated by beams with different parameters such as beam energy. In the second method, films were separately placed at different depths in a phantom and irradiated by the same beams. These methods were used to irradiate films with ions of different LETs. Results For EBT3 film, the dose calibration curves correlated with different LETs appeared to be typical hyperbolic curves with a maximum difference between the curves of ±17% （1σ）. Meanwhile, the shape of the dose calibration curves for EDR2 film appeared to be linear. The values along all these curves were within ±27.4% （1σ） of the value for the average curve. The dose responses of both films were inversely proportional to LETs. The sensitivity of EBT3 film was inversely proportional to the dose, while the sensitivity of EDR2 film showed no relationship with the dose. Conclusions Influenced by the dual factor of LET and dose, the application of EBT3 film was limited in carbon ion. However, without no dose dependence, EDR2 film could be used to measure dose distributions created by single LET carbon ion beam.