| Abstract [eng] |
Novel radiation therapy techniques offer both better tumor control and lower probability of complications. However, more sophisticated techniques require more complex procedure verification because in case of steep dose gradients even minor differences between planned and actual dose distribution can cause severe complications. Dosimetric gels are effectively the only dosimetric method that meets the increasing needs of radiotherapy procedure verification. These dosimeters are able to capture three-dimensional dose distribution with high spatial accuracy. Also, dosimetric gels are tissue-equivalent in terms of absorption of ionizing radiation. Various techniques are used for dose distribution analysis in dosimetric gels, for example, magnetic resonance imaging, computed tomography, optical imaging. Nevertheless, these methods are not optimal - most of them lack spatial resolution, equipment is expensive, complicated, non-modifiable, acquired data is redundant. In this work specialized photospectrometric two-dimensional imaging system for dose distribution analysis in dosimetric gels was designed. The system consists of a spectrometer, data processing software, and a unique cuvette positioning device that enables to acquire spectral information from the entire sample. Designed system achieves 0.125 - 0.15 mm spatial resolution. It is significantly higher when compared to most of the existing dosimetric gel imaging methods, which typically achieve 0.5 – 1 mm spatial resolution. It enables to use the designed system for characterization of dosimetric gels, irradiated with steep dose gradients. Created system was tested with nMAG polymer gel dosimeter, irradiated with a complex shape radiation field using a linear accelerator. For comparison, the same polymer gel was scanned with conventional imaging technique (computed tomography) and alternative scanning techniques (diagnostic ultrasound, flatbed scanning). Created system demonstrates superior performance comparing to both conventional and alternative techniques. Designed system has the highest dose sensitivity, linearity of response and sufficient spatial resolution. High sensitivity of the system was achieved by optimizing the readout wavelength, which in the case of nMAG samples was 509 nm. |
