Dose resolution in radiotherapy polymer gel dosimetry: effect of echo spacing in MRI pulse sequence

In polymer gel dosimetry using magnetic resonance imaging, the uncertainty in absorbed dose is dependent on the experimental determination of T-2 The concept of dose resolution (D-Delta(p)) of polymer gel dosimeters is develo ped and applied to the uncertainty in dose related to the uncertainty in T2 from a range of T2 encountered in polymer gel dosimetry. D-Delta(p) is def ined as the minimal separation between two absorbed doses such that they ma y be distinguished with a given level of confidence, p. The minimum detecta ble dose (MDD) is D-Delta(p) as the dose approaches zero. D-Delta(p) and th e minimum detectable dose both give a quantifiable indication of the likely practical limitations and usefulness of the dosimeter, D-Delta(p) of a pol yacrylamide polymer gel dosimeter is presented for customized 32-echo and s tandard multiple-spin-echo sequences on a clinical MRI scanner. In evaluati ng uncertainties in T-2, a parameter of particular significance in the puls e sequence is the echo spacing (ES). For optimal results, ES should be sele cted to minimize D-Delta(p) over a range of doses of interest in polymer ge l dosimetry,