Geise R A, Schueler B A, Lien W, Jones S C
University of Minnesota, Minneapolis 55455, USA.
Med Phys. 1997 Oct;24(10):1643-6. doi: 10.1118/1.597973.
Skin entrance doses of patients undergoing interventional x-ray procedures are capable of causing skin damage and should be monitored routinely. Single TLD chips are not suitable because the location of maximum skin exposure cannot be predicted. Most photographic films are too sensitive at diagnostic x-ray energies for dosimetry, exhibit temporal changes in response, and require special packaging by the user. We have investigated the suitability of laser heated MgB4O7 TLDs in a polyimide binder in the range of 0.2-20 Gy. These are available in radioluscent arrays up to 30 x 30 cm for direct measurement of patient skin dose. Dose response was compared with a calibrated ion chamber dosimeter. Exposures were made at 60, 90, and 120 kVp, at low (fluoroscopy) and high (DSA) dose rates, and at different beam incidence angles. Longitudinal reproducibility and response to temperature changes during exposure were also checked. The dose response is linear below approximately 6 Gy where the slope starts to increase 2% per Gy. Errors were less than +/- 2% over a 0-80 degrees range of beam incidence angles; less than +/- 3% for both dose rate variations and kVp differences between 70 and 120 kVp. The response was unaffected by temperature changes between 20 and 37 degrees C. Reproducibility is current +/- 7%. MgB4O7 TLD arrays are suitable for patient dosimetry in high dose fluoroscopy procedures if appropriate calibrations are used. Uncertainty in skin dose measurement is less than 10%, which is substantially better than film dosimetry.
接受介入性X射线检查的患者的皮肤入射剂量可能会导致皮肤损伤，因此应进行常规监测。单个热释光剂量计芯片不合适，因为无法预测皮肤最大暴露的位置。大多数摄影胶片在诊断X射线能量下对剂量测定过于敏感，响应会随时间变化，并且需要用户进行特殊包装。我们研究了聚酰亚胺粘合剂中激光加热的MgB4O7热释光剂量计在0.2 - 20 Gy范围内的适用性。这些热释光剂量计可制成尺寸达30×30 cm的放射透明阵列，用于直接测量患者皮肤剂量。将剂量响应与校准后的电离室剂量计进行了比较。在60、90和120 kVp下进行曝光，低剂量率（透视）和高剂量率（数字减影血管造影），以及不同的束入射角。还检查了纵向再现性以及曝光期间对温度变化的响应。在约6 Gy以下剂量响应呈线性，超过此剂量斜率开始以每Gy 2%的速度增加。在0 - 80度的束入射角范围内误差小于±2%；对于剂量率变化以及70至120 kVp之间的千伏峰值差异，误差均小于±3%。在20至37摄氏度之间的温度变化对响应没有影响。当前的再现性为±7%。如果使用适当的校准，MgB4O7热释光剂量计阵列适用于高剂量透视检查程序中的患者剂量测定。皮肤剂量测量的不确定度小于10%，这比胶片剂量测定要好得多。
