Dose measurements in inhomogeneous bone/tissue and lung/tissue phantoms for angiography using synchrotron radiation

For angiography using synchrotron radiation we measured the absorbed dose d istribution in inhomogeneous phantoms with thin LiF:Mg, Cu, P, LiF:Mg, Ti t hermoluminescent dosimeters (TLDs) in tissue and lung substitutes, and with Mg2SiO4:Tb TLDs in bone substitute for 33.32 keV monoenergetic photons fro m synchrotron radiation. The energy responses of the TLDs were measured in air for 10-40 keV monoenergetic photons. The values at 30 keV became smalle r by 30% for LiF:Mg, Cu, P and larger by 22% for Mg2SiO4:Tb than the ratio of the mass energy absorption coefficients of the TLDs to that of air. Thes e values were used to modify the calculated response of the TLDs in each ph antom material. The absorbed dose distribution obtained was compared with t hat calculated using the Monte Carlo transport code EGS4 expanded to a low- energy region, and their agreement was confirmed taking linear polarization into account. In the bone substitute the dose increased by a Factor of 3.9 , while behind the bone the dose decreased drastically because of photon at tenuation. In the lung substitute a slight dose difference from that in sof t tissue was observed because of its different density. The LiF:Mg,Cu,P TLD s exhibited a better energy response, higher sensitivity and wider linear r egions than did the other tissue-equivalent TLDs in the low-energy region.