Comparison of in-phantom dose distributions for coronary angiography usingan x-ray machine and synchrotron radiation

Coronary cineangiography using synchrotron radiation is anticipated, owing to the high intensity and availability of monoenergy. To investigate allowa ble dose levels in clinical application, absorbed dose distribution in a ti ssue substitute phantom for a conventional x-ray machine was measured with thermoluminescent dosimeters at the University of Tsukuba under the practic al conditions used for digital angiography. The dose rate at a 0.5-cm depth was 0.145 Gy/s, and the dose per frame was 0.725 mGy for the irradiation p eriod of 5 ms per frame. For synchrotron radiation, the dose distribution m easurement was made at a 5-GeV AR (Accumulation Ring) of the High Energy Ac celerator Research Organization, in which a polymethylmethacrylate (PMMA) p hantom was irradiated with the strongest beam available at the facility, wh ich was 33.32 keV, 5.2x6.2cm(2) beam. Using this beam, a I-mm-diameter coro nary artery has been visualized at 1% iodine concentration at the AR. Nonho mogeneous strength distribution in the beam was observed in the vertical di rection. The maximum dose rate was 0.556 Gy/s, and it attenuated to 1/3000 at a 30-cm depth in the beam center. At the deep positions, the doses were influenced by the high harmonics, which was confirmed with an EGS4 Monte Ca rlo calculation. Outside the beam, beam contamination on both sides of the main beam affected the doses. For comparison to the x-ray machine, the meas ured dose was analytically converted to that needed for a 5.2x16cm(2) beam that is used for clinical application. The dose rate at 0.5-cm depth was fo und to be 0.215 Gy/s, which is 1.48 times larger than that for x-rays. More over, the attenuation rate in the phantom was significantly greater than th at of the x-ray machine, because of the difference of the energy spectra be tween the x-rays and synchrotron radiation used. (C) 2001 American Associat ion of Physicists in Medicine.