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

Abstract

For angiography using synchrotron radiation we measured the absorbed dosedistribution in inhomogeneous phantoms with thin LiF:Mg, Cu, P, LiF:Mg, Tithermoluminescent dosimeters (TLDs) in tissue and lung substitutes, and withMg2SiO4:Tb TLDs in bone substitute for 33.32 keV monoenergeticphotons from synchrotron radiation. The energy responses of the TLDs weremeasured in air for 10-40 keV monoenergetic photons. The values at 30 keVbecame smaller by 30% for LiF:Mg, Cu, P and larger by 22% for Mg2SiO4:Tb than the ratio of the mass energy absorption coefficients of theTLDs to that of air. These values were used to modify the calculated responseof the TLDs in each phantom material. The absorbed dose distribution obtainedwas compared with that calculated using the Monte Carlo transport code EGS4expanded to a low-energy region, and their agreement was confirmed takinglinear polarization into account. In the bone substitute the dose increased bya factor of 3.9, while behind the bone the dose decreased drastically becauseof photon attenuation. In the lung substitute a slight dose difference fromthat in soft tissue was observed because of its different density. TheLiF:Mg, Cu, P TLDs exhibited a better energy response, higher sensitivity andwider linear regions than did the other tissue-equivalent TLDs in thelow-energy region.