Improved estimates of effective dose equivalent using two optimal anisotropic responding dosimeters

Although the use of two dosimeters, one on the chest and the other on the back, successfully solved the underestimation problem for posterior incident photon beams, the two-dosimeter approach still has some problems-significant overestimations for lateral, overhead, and underfoot beam directions when isotropic-responding dosimeters are used for measurement. A solution to this problem is to intentionally construct the dosimeters to under-respond as the beam direction departs from normal incidence and approaches lateral, overhead, or underfoot beam directions. The objective of this study is to develop a dosimeter that does not significantly overestimate effective dose equivalent (H(E)) for lateral, overhead, and underfoot beam directions, while maintaining good performance for anterior and posterior beam directions. Several dosimeter geometries were investigated using Monte Carlo simulation to find the best geometry using aluminum oxide (Al2O3) as dosimeter attenuator material. Then, the developed Optimal Anisotropic Responding dosimeters were tested for 0.08, 0.30 and 1.00 MeV photon beams of various beam directions. The dosimeters did not overestimate H(E) by more than 80% considering all photon energies and beam directions, which is much less than the overestimation of isotropic-responding dosimeters (202%). The dosimeters also showed similar performance compared to isotropic-responding dosimeters for anterior and posterior beam directions. Finally, the dosimeters were applied to effective dose (E) and the results are compared with those of H(E).