SUITABILITY OF LASER-STIMULATED TLD ARRAYS AS PATIENT DOSE MONITORS IN HIGH-DOSE X-RAY-IMAGING

Skin entrance doses of patients undergoing interventional x-ray proced ures are capable of causing skin damage and should be monitored routin ely. Single TLD chips are not suitable because the location of maximum skin exposure cannot be predicted. Most photographic films are too se nsitive at diagnostic x-ray energies for dosimetry, exhibit temporal c hanges in response, and require special packaging by the user. We have investigated the suitability of laser heated MgB4O7 TLDs in a polyimi de binder in the range of 0.2-20 Gy. These are available in radiolusce nt arrays up to 30X30 cm for direct measurement of patient skin dose. Dose response was compared with a calibrated ion chamber dosimeter. Ex posures were made at 60, 90, and 120 kVp, at low (fluoroscopy) and hig h (DSA) dose rates, and at different beam incidence angles. Longitudin al 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 degree range of beam incidence angles; less than +/ -3% for both dose rate variations and kVp differences between 70 and 1 20 kVp. The response was unaffected by temperature changes between 20 and 37 degrees C. Reproducibility is currently +/-7%. MgB4O7 TLD array s are suitable for patient dosimetry in high dose fluoroscopy procedur es if appropriate calibrations are used. Uncertainty in skin dose meas urement is less than 10%, which is substantially better than film dosi metry. (C) 1997 American Association of Physicists in Medicine.