Dose response of storage phosphor plates exposed to megavoltage photon beams

Abstract

The BaFBrI:Eu2+ storage phosphor plate (SPP) is a reusable radiation image detector, widely used in diagnostic computed radiography, x-ray crystallography and radioactive tracer studies. When exposed to ionizing radiation, the SPP stores a latent image until it is scanned with a red reading laser which causes blue photostimulated luminescent (PSL) photons to be emitted. The mechanism of formation of the latent image is still poorly understood, especially for megavoltage photon beams. In order to gain insight into this mechanism and aid applications to high-energy beam dosimetry, the authors have directly determined the SPP generation efficiency, W, the energy required to produce one quantum of emitted PSL when it is irradiated by 60Co and 6 MV photon beams. This was done in four steps: 1. The SPP, in a water-equivalent plastic (WEP) phantom, was exposed to a 60Co or 6 MV beam, which had been calibrated to give a known absorbed dose to water in a water phantom at the position of the sensitive layer of the SPP. 2. Monte Carlo simulations were used to calculate the ratio of the dose to the sensitive layer in the WEP phantom to the dose to water at the same position in a water phantom. 3. A bleaching experiment was used to determine the number of photons emitted by a plate given a known dose. 4. The generation efficiency was calculated from the number of photons and the dose. This method is much more direct than previous calculations for kilovoltage x-ray beams based on quantum noise analysis. W was found, within experimental uncertainty, to be 190 eV for 60Co and 160 eV for 6 MV, independent of dose. The values for kilovoltage x-ray beams determined previously agree, within their large uncertainty, with these values for megavoltage beams.

Quantitative megavoltage radiation therapy dosimetry using the storage phosphor KCl:Eu2+

“…We expect that further materials processing optimization, including synthesis conditions, particle morphology, doping uniformity, etc., will result in materials that provide sufficient signal strength over a clinically relevant dose range for a KCl: Eu 2+ dosimeter with thickness of the order of 10 m. 34 This effort will be supported in part by the intrinsic low background noise associated with storage phosphor techniques. 23,35,36 One advantage of having a reusable dosimeter is that characteristic curves can be predetermined and a library of curves stored. For example, if a dosimeter is used for a specific clinical case, the appropriate sensitometric curve could be selected from a stored library.…”

Theoretical and empirical investigations of for nearly water‐equivalent radiotherapy dosimetry

“…where W KCl was the work function for KCl: Eu 2+ , the energy that must be absorbed from the beam to produce a PSL photon, was the light collection efficiency, and Q E was the PMT quantum efficiency. In order to obtain W KCl , the sensitivity of a thick KCl: Eu 2+ film was compared against a commercial BaFBr 0.85 I 0.15 :Eu 2+ -based SPF ͑Fuji HRIII͒, the work function of which, W Ba , was previously measured by Li et al 22 The thick KCl: Eu 2+ film was produced in-house using a tape casting method. In brief, a homogeneous suspension containing KCl: Eu 2+ storage phosphor particles, liquid vehicle, and polymer binder was formed and subsequently cast by "doctor-blade" onto a polyethylene terephthalate substrate to form a 150 m thick KCl: Eu 2+ film with coating weight of 28 mg/ cm 2 .…”

Performance of KCl:Eu2+storage phosphor dosimeters for low-dose measurements

“…A 0.01 cGy dose-to-water yielded a net signal level at about 2 µV after background subtraction. Other type A uncertainties (Li et al, 2007) associated with KCl:Eu 2+ prototypes include positioning uncertainty due to manual placement of dosimeters in the readout system, reproducibility of the reader, and performance variation among dosimeters. These uncertainties can certainly be reduced by improved instrumentation and materials engineering.…”