Angular dependence of the optically stimulated luminescent dosimeter

Abstract

Objective To study the angular dependence of optically stimulated luminescent dosimeter (OSLD) with solid phantoms under SSDL radiation level 60Co radiation field, and to discuss the possibility of OSLD in volumetric modulated arc therapy (VMAT) and other rotating irradiation dose audit. Methods OSLDs were embedded in the two phantoms with the same size and material, respectively. The phantom 1 was set to make the first OSLD perpendicular to the beam, and the phantom 2 was set to make the second OSLD parallel to the beam. The OSLDs were irradiated at 8 angles: 0°, 45°, 90°, 135°, 180°, –45°, –90, –135°. The counts of the OSLSs were read and the response of each angle which normalized to 0° were calculated. Results When the OSLDs are perpendicular to the beam, the angular response is between –6.76% 〜+1.5%, with the maximum angular dependence at 90° and –90°. When the OSLDs are parallel to the beam, the angular response is between –1.74%〜+1.67%, below 2%. Conclusion It is better to correct the sensitivity of dosimeters by Element Correction Factors (ECF) for dose audit. Under the condition of rotating irradiation, OSLD shoud be set parallel to the beam, which can better reduce the influence of angular dependence and facilitate further application research of VMAT dose audit. 摘要： 目的 结合定制固体模体研宄光致发光剂量计(OSLD)在放疗水平 60Co标准辐射场中的角响应性能, 探讨OSLD在容积旋转调强放射治疗(VMAT)等旋转照射剂量核查中应用的可行性。 方法 将OSLD嵌入2个外观尺寸以 及材料均相同的定制固体模体, 模体1使OSLD与射线垂直, 模体2使OSLD与射线平行, 照射8个角度：0°、45°、 90°、135°、180°、–45°、–90°和–135°, 读取每个角度的OSLD计数, 计算每个角度相对于0°的角响应值。 结果 当OSLD 垂直于射线照射时, 角响应在–6.76%〜+1.5%, 90°和–90°角响应最大;当OSLD平行于射线照射时, 角响应在–1.74%〜 +1.67%, 均在± 2%以内。 结论 在实际工作中, 应先计算元件校正因子(ECF), 校正各剂量计对射线的灵敏度, 旋转 照射条件下, 将OSLD平行于射线入射方向放置, 能更好地降低角响应影响, 便于进一步开展VMAT剂量核查应用研宄。