Laser Light Trapping Phenomenon in a 3D Radiotherapy Polymer Gel Dosimeter

Abstract

This paper aims to explain the phenomenon of laser light trapping (LLT) in a 3D polymer gel dosimeter. A VIC-T polymer gel dosimeter containing 17% N-vinylpyrrolidone, 8% N,N′-methylenebisacrylamide, 12% tert-butyl alcohol, 5% gelatine, 0.02% hydroquinone and 14 mM tetrakis(hydroxymethyl)phosphonium chloride was used in this study. It was exposed to green laser light with a wavelength of 532 nm. A film was recorded during the exposure. After exposure, Raman spectroscopy was used to study the reactions taking place inside the dosimeter. The obtained results were used to explain what the LLT phenomenon is, what are the consequences for the dosimeter in which such a phenomenon occurs, and what dosimeter components play an important role in the occurrence of LLT. In addition, the conditions under which 3D polymer gel dosimeters can be measured using optical computed tomography at short wavelengths of visible laser light are indicated.

Fast Isocenter Determination Using 3D Polymer Gel Dosimetry with Kilovoltage Cone-Beam CT Reading and the PolyGeVero-CT Software Package for Linac Quality Assurance in Radiotherapy

“…The valve was intended to improve the performance of the dosimeters. Note that improper containers for 3D gel dosimeters can cause gel dosimeter cracking and the formation of voids, which have a negative impact on the CT (or MR) image quality and the calculation of results (e.g., see Figure 7C in [ 45 ]).…”

Validation of complex radiotherapy techniques using polymer gel dosimetry

“…In principle, such internal density changes may cause volume variations or even cracks in the gel. In these cases, a special container design might be necessary to release the internal mechanical stress in the gel (Kozicki et al 2021a) In addition, also on-board kilo-voltage (kV) CBCT was used to validate geometrical aspects of the dose distribution (Adamson et al 2019). With the relatively low sensitivity of the CT-evaluation, however, it becomes challenging to maintain sufficient signal-to-noise with adequate spatial resolution.…”