Estimating the effects on the dose distribution through the Bragg Peak degradation of lung tissue in proton therapy of thoracic tumors
Particle therapy offers to be a promising therapeutic option for tumors in the lung like Non-small cell lung cancer (NSCLC). However, the irradiation of NSCLCs with protons or carbon ions poses different challenges. The movement of the tumor, the heart and the entire thorax through breathing and the...
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|Summary:||Particle therapy offers to be a promising therapeutic option for tumors in the lung like Non-small cell lung cancer (NSCLC). However, the irradiation of NSCLCs with protons or carbon ions poses different challenges. The movement of the tumor, the heart and the entire thorax through breathing and the heartbeat requires a motion mitigated radiation application. In addition, the microscopic structure of the lung tissue holds further uncertainties of the calculation of the optimized dose distribution.
In clinical CTs, on which treatment planning and dose calculation is based, the micrometer-sized air-filled alveoli of the lungs are not fully resolved, but are mapped through a medium density. As each particle of the beam passes a slightly different composition of air and tissue which leads to a slightly different range of the particles, the Bragg peak is degraded when irradiating such a heterogeneous tissue as lung.
If this degradation of the Bragg peak is not taken into account into treatment planning, it can potentially lead to an underdose in the target volume and thus to a loss in tumor control. Additionally, the degradation can also lead to a higher dose in the organs at risk and normal tissue, endangering the success of the therapy by a higher toxicity of the treatment.
In this dissertation, the effects of the Bragg Peak degradation on the dose distribution are calculated and analyzed so that an assessment of the effects for the clinical routine is available. For this purpose, CT images are manipulated with the help of a density modulation function, which modulates the density of the macroscopic lung voxel to reproduce the microscopic effect. Thus, a direct comparison between the dose distributions with and without the degrading effect is possible. Various dependencies like the tumor size, position and shape are systematically examined and the results of the degradation on clinical plans are presented for five patients. Hence, the clinical relevance can be estimated and assessed.
In addition, measurements are presented which show the introduced material property of the "modulation power" of lung tissue. On the basis of this data, the uncertainties of the presented calculation and analysis can be reduced and estimated better. In addition, a mathematical model is presented which allows to estimate the modulation power on the basis of a clinical CT histogram analysis.
Together, the works presented offer a basis for the patient-specific translation of the Bragg peak degradation of lung tissue into the clinical treatment planning procedure.|
|Physical Description:||163 Pages|