Improvement of sensitivity of X-ray CT reading method for polymer gel in radiation therapy

Abstract

Background: Three dimensional (3D) dosimetry methods are useful for advanced radiotherapy techniques such as stereotactic radiosurgery (SRS) and high dose rate (HDR) brachytherapy. Polymer gel is one of the more reliable 3D dosimetry techniques. More studies are needed to improve the efficiency of polymer gels for their application in dosimetry.

Aim: In the current study, the best protocol for reading of N-isopropyl acrylamide (NIPAM) polymer gel by X-ray computed tomography (CT) was implemented for application in radiotherapy.

Material and methods: The NIPAM gel was made and irradiated by 6 MV. Its reading was done by the X-ray CT after 24 h and the information examined by using the MATLAB software. In the present work, the different effects of slice thicknesses and voltages were investigated for its lower toxicity of NIPAM polymer gel. The results of a recipe of different filtering on the response curve of polymer gel was investigated.

Results: The measured dose sensitivity was ${\Delta N}_{CT}\left(H\right)$ = 0.29 ± 0.01 $\left(H{Gy}^{-1}\right)$ for the NIPAM dosimeter. The best sensitivity was achieved for 120 kVp and the slice thickness of 10 mm. The greater slice thickness gained more desirable sensitivity. This process was repeated by using different filtering with different thicknesses to obtain the best sensitivity.

Conclusions: The sensitivity of X-ray CT reading technique of NIPAM Polymer gel depended on the slice thickness and kVp. The wiener2 filtering was useful to improving sensitivity.

Keywords: NIPAM polymer gel dosimeter; Radiation therapy; X-ray computed tomography (CT).