Flexible optically stimulated luminescence band for 1D in vivo radiation dosimetry

Abstract

In vivo dosimetry helps ensure the accuracy of radiation treatments. However, standard techniques are only capable of point sampling, making it difficult to accurately measure dose variation along curved surfaces in a continuous manner. The purpose of this work is to introduce a flexible dosimeter band and validate its performance using pre-clinical and clinical x-ray sources. Dosimeter bands were fabricated by uniformly mixing BaFBr:Eu storage phosphor powders into a silicone based elastomer. An optical readout device with dual-wavelength excitation was designed and built to correct for non-uniform phosphor density and extract accurate dose information. Results demonstrated significant correction of the non-uniform readout signal and excellent dose linearity up to 8 Gy irradiation using a pre-clinical 320 kV x-ray system. Beam profile measurements were demonstrated over a long distance of ~30 cm by placing multiple dosimeters in a single line and stitching the results. The performance of the dosimeters was also tested using a clinical linear accelerator (6 MV) and compared to radiochromic film. Once bias corrected, the bands displayed a linear dose response over the 1.02-9.36 Gy range (R ² > 0.99). The proposed system can be further improved by reducing the size of the readout beam and by more uniformly mixing the phosphor powder with the elastomer. We expect this technique to find application for large-field treatments such as total-skin irradiation and total-body irradiation.

Figure 1.

Schematic diagram of (a) the fabrication steps for the flexible dosimeter bands and (b) photographs of the dosimeter bands placed on a flat surface or rolled into a spool.

Figure 2.

(a) Photograph and (b) schematic diagram of the dosimeter readout device. The dosimeter is initially scanned with the red laser sheet for OSL signal, then with the UV source for PL signal.

Figure 3.

Example of intensity profiles measured using a single dosimeter (8 Gy exposure). (a) OSL signal excited with red laser sheet; (b) PL signal excited with UV light sheet, and (c) calibrated readout obtained by computing the ratio of OSL to PL signal. The x-axis is the spatial coordinate from the start to the end of the dosimeter band.

Figure 4.

Dose response graph of dosimeters exposed to 0 – 8 Gy of X-ray irradiation. The data from 8 Gy is excluded from the linear regression line since slight saturation of the signal was observed. Error bars represent ± 1 standard deviation, from 10 dosimeter readings.

Figure 5.

Graph representing beam profile of a kV cabinet X-ray. Three dosimeters, each 10 cm long, were placed in series to cover ~30 cm.

Figure 6.

Factors affecting uncertainty in the dose response curve includes (a) fading and (b) afterglow. The uncertainty may be reduced if dose readout is performed consistently after irradiation and after an extended period of time (e.g., 10 minutes).

Figure 7.

Graph representing (a) the response of the dosimeter system to a narrow X-ray beam of varying width, and (b) the measured FWHM as a function of the collimator opening size. The adjustable collimator size is achieved by opening the jaws of a stainless-steel caliper in the X-ray beam path.

Figure 8.

(a) Raw data of the dosimeter bands and Gafchromic film after exposure to 6 MV linac beam (staircase field, 1.02 Gy to 9.36 Gy), and (b) the corresponding dose response curve corrected for bias and non-linearity. Data from the three dosimeters were bias-corrected and stitched to form a single 1-D line. Corrected dose curves of both the Gafchromic film and the dosimeter bands demonstrate good linearity (R² > 0.99).