When Is High Level-Control Fluoroscopy Not High Dose-Rate Fluoroscopy?
D Bednarek1*, J PazLozada2, S Rudin1, (1) Univ. at Buffalo (SUNY) School of Med., Buffalo, NY, (2) Fundacion Valle del Lili, Cali, ColumbiaSU-E-I-26 Sunday 3:00PM - 6:00PM Room: Exhibit Hall
Purpose: To examine the logic of the current use of high level control (HLC) mode as set up on many fluoroscopic systems.
Methods:Use of HLC requires special means of activation and a continuous audible alarm and implies a higher dose rate of fluoroscopy. To examine if this implication is true in practice, we performed a survey of the entrance air kerma to an abdomen phantom as well as the maximum air kerma for a number of fluoroscopic machines operated under automatic exposure-rate control using standard (non-HLC) fluoroscopy and HLC fluoroscopy modes. Measurements were made using the abdomen phantom of the ACR Radiography / Fluoroscopy Accreditation Program with the ionization chamber placed either 15 cm from isocenter or at the FDA compliance point. For the maximum dose rate determination a 3 mm thick sheet of lead was placed over the phantom. The results presented are for 7 different mobile and fixed c-arm units operated in available protocol and magnification modes.
Results:For the abdomen phantom, the machines showed widely different entrance air kerma rates and response to changes in exposure mode and protocols. Our survey found: c-arm units which gave a lower dose rate under HLC fluoroscopy than standard fluoroscopy when used with the abdomen phantom; units for which the HLC dose rate for some protocols was less than for standard fluoroscopy with other protocols; and units which did not exceed 88 mGy/min for some protocols even with lead in the beam when operating under HLC. In all cases, the audible alarm signaled HLC fluoroscopy with the implication of high dose rate.
Conclusion:The audible alarm activated by HLC can be misleading and counterproductive since dose rates under HLC can be lower than standard fluoroscopy on the same machine. HLC does not always mean high dose-rate fluoroscopy.
Funding Support, Disclosures, and Conflict of Interest: JP was supported by the Fulbright Scholar Program.