Further developments in 2D optically stimulated luminescence dosimetry based on Al2O3 and MgB4O7

Abstract

Scope and Method of Study: The objective of this work is to explore potential improvements in 2D OSL dosimetry. These include the introduction of Tikhonov regularization in the pixel bleeding algorithm, which was investigated based both on simulated data as well as experimental results obtained using a 6 MV linear accelerator (linac) and an Accuray CyberKnife. The feasibility of using of Al2O3:C and Al2O3:C,Mg for its application in dosimetry in the presence of magnetic fields was tested. Finally, initial results of newly developed MgB4O7:Ce,Li films for 2D optically stimulated luminescence dosimetry are presented.

Findings and Conclusions: The results show that the implementation of Tikhonov regularization improves the image noise and resolves the directional dependence in the OSL images when compared to the Least Squares algorithm. The initial measurements of off-central ray ratios (OCR), output factors (OF's), and tissue phantom ratios (TPR) in CyberKnife shows good agreement with the measurements using the commercial stereotactic diode. The initial tests using the Al2O3 OSLD's in MR linac show that the detectors do not attenuate the beam, independent of angle of irradiation within 1.4%. The gamma analysis of IMRT treatment plans and the OSL images show a good passing rate for both 3% - 3 mm and 2% - 2 mm gamma criteria. The initial studies of MgB4O7:Ce,Li films demonstrate the possibility of 2D dosimetry for radiotherapy applications with many advantages over Al2O3:C or Al2O3:C,Mg films. MBO films show no pixel bleeding in the OSL images, has a linear dose response up to 10 Gy with steep dose gradients, has background equivalent dose of <0.5 mGy. However, it suffers from fading and sensitization. In conclusion, this work demonstrates OSL films have huge potential for its 2D dosimetry in both small fields and MR guided radiotherapy especially with development of new OSL materials to overcome the challenges with the current OSL materials.