Fricke-Xylenol orange-Gelatin gel characterization with dual wavelength cone-beam optical CT scanner for applications in stereotactic and dynamic radiotherapy.

Purpose: This study is about the development of a new dual wavelength reading method of Fricke-Xylenol orange-Gelatin (FXG) gel dosimeters on the Vista16™ optical Computed Tomography (CT) scanner to perform 3D dose distribution measurements in stereotactic and dynamic radiotherapy treatments.

Methods: The dosimetric characteristics of an optimized FXG gel composition and its optical CT readout have been evaluated. A dual wavelength reading method has been developed on the CT scanner at wavelengths 590 nm and 633 nm. Small-field dose profile measurements with FXG gel and microDiamond (PTW) detectors were compared by γ-index analysis (0.5%/0.5 mm) to validate this method.

Results: This reading method exhibits linear calibration curves in the 0-4 Gy and 2-10 Gy dose ranges at 590 nm and 633 nm respectively. The absorbed dose values below 4 Gy, measured at 590 nm, and those above 4 Gy, measured at 633 nm, are combined to plot a complete profile. A γ passing rate of 93.4% was achieved.

Conclusions: The new reading method of FXG gel dosimeters has been implemented on the Vista16™ scanner to span absorbed doses representative of stereotactic and dynamic radiotherapy treatments and enable 3D measurements in tumor volumes and surrounding healthy tissues. Small-field profile measurements validated this reading method as FXG gel dosimeters and microDiamond detectors were in very close agreement. This dosimetric method is a promising candidate for 3D quality assurance end-to-end tests in stereotactic and dynamic radiotherapy.